From b22f9684326910c85512a3f8a828aeae342025c7 Mon Sep 17 00:00:00 2001
Subject: Add specialized hashmap version of the long type

---
 .../cpu/aarch64/vm_version_aarch64.hpp        |    5 +
 src/hotspot/share/cds/filemap.cpp             |    4 +-
 src/hotspot/share/cds/heapShared.hpp          |    3 +-
 src/hotspot/share/cds/metaspaceShared.cpp     |    7 +-
 src/hotspot/share/classfile/classLoader.cpp   |   51 +
 src/hotspot/share/classfile/classLoader.hpp   |    3 +
 .../classfile/systemDictionaryShared.cpp      |    3 +
 src/hotspot/share/oops/symbol.hpp             |    4 +
 src/hotspot/share/runtime/arguments.cpp       |    7 +
 src/hotspot/share/runtime/globals.hpp         |    6 +
 src/hotspot/share/runtime/java.cpp            |    6 +
 src/hotspot/share/runtime/java.hpp            |    2 +
 src/hotspot/share/runtime/vm_version.cpp      |    8 +
 test/jdk/java/util/HashMap/HashMap.java       | 3798 +++++++++++++++++
 test/jdk/java/util/HashMap/LinkedHashMap.java |  798 ++++
 15 files changed, 4699 insertions(+), 6 deletions(-)
 create mode 100644 test/jdk/java/util/HashMap/HashMap.java
 create mode 100644 test/jdk/java/util/HashMap/LinkedHashMap.java

diff --git a/src/hotspot/cpu/aarch64/vm_version_aarch64.hpp b/src/hotspot/cpu/aarch64/vm_version_aarch64.hpp
index 46c77e48b..eac0db870 100644
--- a/src/hotspot/cpu/aarch64/vm_version_aarch64.hpp
+++ b/src/hotspot/cpu/aarch64/vm_version_aarch64.hpp
@@ -142,6 +142,11 @@ public:
   static int cpu_variant()                    { return _variant; }
   static int cpu_revision()                   { return _revision; }
 
+  static bool is_hisi_enabled() {
+    return (_cpu == CPU_HISILICON &&
+            (_model == 0xd01 || _model == 0xd02 || _model == 0xd22 || _model == 0xd45));
+  }
+
   static bool model_is(int cpu_model) {
     return _model == cpu_model || _model2 == cpu_model;
   }
diff --git a/src/hotspot/share/cds/filemap.cpp b/src/hotspot/share/cds/filemap.cpp
index 76e078d12..13a9f22a9 100644
--- a/src/hotspot/share/cds/filemap.cpp
+++ b/src/hotspot/share/cds/filemap.cpp
@@ -1807,8 +1807,8 @@ MemRegion FileMapInfo::get_heap_regions_range_with_current_oop_encoding_mode() {
 // open archive objects.
 void FileMapInfo::map_heap_regions_impl() {
   if (!HeapShared::is_heap_object_archiving_allowed()) {
-    log_info(cds)("CDS heap data is being ignored. UseG1GC, "
-                  "UseCompressedOops and UseCompressedClassPointers are required.");
+    log_info(cds)("CDS heap data is being ignored. UseG1GC, UseCompressedOops, "
+                  "UseCompressedClassPointers and !UsePrimHashMap are required.");
     return;
   }
 
diff --git a/src/hotspot/share/cds/heapShared.hpp b/src/hotspot/share/cds/heapShared.hpp
index 74de74d6c..f7a1a004f 100644
--- a/src/hotspot/share/cds/heapShared.hpp
+++ b/src/hotspot/share/cds/heapShared.hpp
@@ -352,7 +352,8 @@ private:
   static void run_full_gc_in_vm_thread() NOT_CDS_JAVA_HEAP_RETURN;
 
   static bool is_heap_object_archiving_allowed() {
-    CDS_JAVA_HEAP_ONLY(return (UseG1GC && UseCompressedOops && UseCompressedClassPointers);)
+    CDS_JAVA_HEAP_ONLY(return (UseG1GC && UseCompressedOops &&
+                               UseCompressedClassPointers && !UsePrimHashMap);)
     NOT_CDS_JAVA_HEAP(return false;)
   }
 
diff --git a/src/hotspot/share/cds/metaspaceShared.cpp b/src/hotspot/share/cds/metaspaceShared.cpp
index f4c8d0f81..748166480 100644
--- a/src/hotspot/share/cds/metaspaceShared.cpp
+++ b/src/hotspot/share/cds/metaspaceShared.cpp
@@ -785,10 +785,11 @@ void VM_PopulateDumpSharedSpace::dump_java_heap_objects(GrowableArray<Klass*>* k
   if(!HeapShared::is_heap_object_archiving_allowed()) {
     log_info(cds)(
       "Archived java heap is not supported as UseG1GC, "
-      "UseCompressedOops and UseCompressedClassPointers are required."
-      "Current settings: UseG1GC=%s, UseCompressedOops=%s, UseCompressedClassPointers=%s.",
+      "UseCompressedOops, UseCompressedClassPointers and !UsePrimHashMap are required."
+      "Current settings: UseG1GC=%s, UseCompressedOops=%s, "
+      "UseCompressedClassPointers=%s, UsePrimHashMap=%s",
       BOOL_TO_STR(UseG1GC), BOOL_TO_STR(UseCompressedOops),
-      BOOL_TO_STR(UseCompressedClassPointers));
+      BOOL_TO_STR(UseCompressedClassPointers), BOOL_TO_STR(UsePrimHashMap));
     return;
   }
   // Find all the interned strings that should be dumped.
diff --git a/src/hotspot/share/classfile/classLoader.cpp b/src/hotspot/share/classfile/classLoader.cpp
index 6e9b9bcdf..6480cd6f6 100644
--- a/src/hotspot/share/classfile/classLoader.cpp
+++ b/src/hotspot/share/classfile/classLoader.cpp
@@ -142,6 +142,9 @@ ClassPathEntry* ClassLoader::_jrt_entry = NULL;
 
 ClassPathEntry* volatile ClassLoader::_first_append_entry_list = NULL;
 ClassPathEntry* volatile ClassLoader::_last_append_entry  = NULL;
+
+ClassPathEntry* ClassLoader::_prim_collection_entry = NULL;
+
 #if INCLUDE_CDS
 ClassPathEntry* ClassLoader::_app_classpath_entries = NULL;
 ClassPathEntry* ClassLoader::_last_app_classpath_entry = NULL;
@@ -628,6 +631,36 @@ bool ClassLoader::is_in_patch_mod_entries(Symbol* module_name) {
   return false;
 }
 
+// Set up the _prim_collection_entry if UsePrimHashMap
+void ClassLoader::set_prim_collection_path(JavaThread *current) {
+  if (!UsePrimHashMap) {
+    return;
+  }
+  const char *prim_collection_jar = "primcollection.jar";
+  char jvm_path[JVM_MAXPATHLEN];
+  os::jvm_path(jvm_path, sizeof(jvm_path));
+  const int trunc_times = 2; // set path/lib/server/libjvm.so to path/lib
+  for (int i = 0; i < trunc_times; ++i) {
+    char *end = strrchr(jvm_path, *os::file_separator());
+    if (end != NULL) *end = '\0';
+  }
+
+  size_t jvm_path_len = strlen(jvm_path);
+  if (jvm_path_len < JVM_MAXPATHLEN - strlen(os::file_separator()) - strlen(prim_collection_jar)) {
+    jio_snprintf(jvm_path + jvm_path_len,
+                 JVM_MAXPATHLEN - jvm_path_len,
+                 "%s%s", os::file_separator(), prim_collection_jar);
+  }
+  char* error_msg = NULL;
+  jzfile* zip = open_zip_file(jvm_path, &error_msg, current);
+  if (zip != NULL && error_msg == NULL) {
+    _prim_collection_entry = new ClassPathZipEntry(zip, jvm_path, false, false);
+    log_info(class, load)("primcollection path: %s", jvm_path);
+  } else {
+    UsePrimHashMap = false;
+  }
+}
+
 // Set up the _jrt_entry if present and boot append path
 void ClassLoader::setup_bootstrap_search_path_impl(JavaThread* current, const char *class_path) {
   ResourceMark rm(current);
@@ -677,6 +710,8 @@ void ClassLoader::setup_bootstrap_search_path_impl(JavaThread* current, const ch
       update_class_path_entry_list(current, path, false, true, false);
     }
   }
+
+  set_prim_collection_path(current);
 }
 
 // During an exploded modules build, each module defined to the boot loader
@@ -1183,6 +1218,22 @@ InstanceKlass* ClassLoader::load_class(Symbol* name, bool search_append_only, TR
       stream = search_module_entries(THREAD, _patch_mod_entries, class_name, file_name);
     }
   }
+  // Load Attempt: primcollection.jar for PrimHashMapRelatedClass
+  if (UsePrimHashMap && (NULL == stream) && name->is_primhashmap_related_class()) {
+    static bool is_first_loading = true;
+    static bool is_first_loading_succeeded = false;
+    stream = _prim_collection_entry->open_stream(THREAD, file_name);
+    if (!is_first_loading) {
+      // exit when some loads succeed while some fail
+      if ((is_first_loading_succeeded && stream == nullptr) ||
+          (!is_first_loading_succeeded && stream != nullptr)) {
+        vm_exit_during_prim_collection_loading();
+      }
+    } else {
+      is_first_loading = false;
+      is_first_loading_succeeded = (stream != nullptr);
+    }
+  }
 
   // Load Attempt #2: [jimage | exploded build]
   if (!search_append_only && (NULL == stream)) {
diff --git a/src/hotspot/share/classfile/classLoader.hpp b/src/hotspot/share/classfile/classLoader.hpp
index bac23a9dd..7c1c68317 100644
--- a/src/hotspot/share/classfile/classLoader.hpp
+++ b/src/hotspot/share/classfile/classLoader.hpp
@@ -216,6 +216,8 @@ class ClassLoader: AllStatic {
   // Last entry in linked list of appended ClassPathEntry instances
   static ClassPathEntry* volatile _last_append_entry;
 
+  static ClassPathEntry* _prim_collection_entry;
+
   // Info used by CDS
   CDS_ONLY(static ClassPathEntry* _app_classpath_entries;)
   CDS_ONLY(static ClassPathEntry* _last_app_classpath_entry;)
@@ -243,6 +245,7 @@ class ClassLoader: AllStatic {
   static void setup_bootstrap_search_path(JavaThread* current);
   static void setup_bootstrap_search_path_impl(JavaThread* current, const char *class_path);
   static void setup_patch_mod_entries();
+  static void set_prim_collection_path(JavaThread *current);
   static void create_javabase();
 
   static void* dll_lookup(void* lib, const char* name, const char* path);
diff --git a/src/hotspot/share/classfile/systemDictionaryShared.cpp b/src/hotspot/share/classfile/systemDictionaryShared.cpp
index c15e8f4df..8a6343fc3 100644
--- a/src/hotspot/share/classfile/systemDictionaryShared.cpp
+++ b/src/hotspot/share/classfile/systemDictionaryShared.cpp
@@ -2580,6 +2580,9 @@ SystemDictionaryShared::find_record(RunTimeSharedDictionary* static_dict, RunTim
 }
 
 InstanceKlass* SystemDictionaryShared::find_builtin_class(Symbol* name) {
+  if (UsePrimHashMap && name->is_primhashmap_related_class()) {
+    return NULL;
+  }
   const RunTimeSharedClassInfo* record = find_record(&_builtin_dictionary, &_dynamic_builtin_dictionary, name);
   if (record != NULL) {
     assert(!record->_klass->is_hidden(), "hidden class cannot be looked up by name");
diff --git a/src/hotspot/share/oops/symbol.hpp b/src/hotspot/share/oops/symbol.hpp
index 96562d08a..003422ca1 100644
--- a/src/hotspot/share/oops/symbol.hpp
+++ b/src/hotspot/share/oops/symbol.hpp
@@ -194,6 +194,10 @@ class Symbol : public MetaspaceObj {
   }
   bool equals(const char* str) const { return equals(str, (int) strlen(str)); }
 
+  bool is_primhashmap_related_class() const {
+    return starts_with("java/util/HashMap") || starts_with("java/util/LinkedHashMap");
+  }
+
   // Tests if the symbol starts with the given prefix.
   bool starts_with(const char* prefix, int len) const {
     return contains_utf8_at(0, prefix, len);
diff --git a/src/hotspot/share/runtime/arguments.cpp b/src/hotspot/share/runtime/arguments.cpp
index f24cabb11..357ad4aca 100644
--- a/src/hotspot/share/runtime/arguments.cpp
+++ b/src/hotspot/share/runtime/arguments.cpp
@@ -2969,6 +2969,13 @@ jint Arguments::parse_each_vm_init_arg(const JavaVMInitArgs* args, bool* patch_m
     LogConfiguration::configure_stdout(LogLevel::Info, true, LOG_TAGS(class, path));
   }
 
+  if (DumpSharedSpaces && UsePrimHashMap) {
+    warning("UsePrimHashMap is confilict with -Xshare:dump. ignoring UsePrimHashMap.");
+    if (FLAG_SET_CMDLINE(UsePrimHashMap, false) != JVMFlag::SUCCESS) {
+      return JNI_EINVAL;
+    }
+  }
+
   fix_appclasspath();
 
   return JNI_OK;
diff --git a/src/hotspot/share/runtime/globals.hpp b/src/hotspot/share/runtime/globals.hpp
index 680e78c04..4f02cb31a 100644
--- a/src/hotspot/share/runtime/globals.hpp
+++ b/src/hotspot/share/runtime/globals.hpp
@@ -2129,6 +2129,12 @@ const intx ObjectAlignmentInBytes = 8;
   JFR_ONLY(product(ccstr, StartFlightRecording, NULL,                       \
           "Start flight recording with options"))                           \
                                                                             \
+  product(bool, UsePrimHashMap, false, EXPERIMENTAL,                        \
+          "The Prim HashMap is a specialized version for long key. "        \
+          "Long-Key HashMap can benefit from this in most scenarios."       \
+          "Note: The debugging of HashMap.java is inaccurate"               \
+          " when UsePrimHashMap is enabled.")                               \
+                                                                            \
   product(bool, UseFastSerializer, false, EXPERIMENTAL,                     \
           "Cache-based serialization.It is extremely fast, but it"          \
           "can only be effective in certain scenarios.")                    \
diff --git a/src/hotspot/share/runtime/java.cpp b/src/hotspot/share/runtime/java.cpp
index a77f30b8c..ccfb0806d 100644
--- a/src/hotspot/share/runtime/java.cpp
+++ b/src/hotspot/share/runtime/java.cpp
@@ -690,6 +690,12 @@ void vm_exit_during_cds_dumping(const char* error, const char* message) {
   vm_abort(false);
 }
 
+void vm_exit_during_prim_collection_loading() {
+  tty->print_cr("Error occurred during loading prim collection classes: must load all or none from primcollection.jar");
+  // no need to dump core
+  vm_abort(false);
+}
+
 void vm_notify_during_shutdown(const char* error, const char* message) {
   if (error != NULL) {
     tty->print_cr("Error occurred during initialization of VM");
diff --git a/src/hotspot/share/runtime/java.hpp b/src/hotspot/share/runtime/java.hpp
index ad179662f..e796fa84c 100644
--- a/src/hotspot/share/runtime/java.hpp
+++ b/src/hotspot/share/runtime/java.hpp
@@ -59,6 +59,8 @@ extern void vm_shutdown_during_initialization(const char* error, const char* mes
 
 extern void vm_exit_during_cds_dumping(const char* error, const char* message = NULL);
 
+extern void vm_exit_during_prim_collection_loading();
+
 /**
  * With the integration of the changes to handle the version string
  * as defined by JEP-223, most of the code related to handle the version
diff --git a/src/hotspot/share/runtime/vm_version.cpp b/src/hotspot/share/runtime/vm_version.cpp
index 33a5c792c..1e6756aaa 100644
--- a/src/hotspot/share/runtime/vm_version.cpp
+++ b/src/hotspot/share/runtime/vm_version.cpp
@@ -31,6 +31,14 @@
 void VM_Version_init() {
   VM_Version::initialize();
 
+#ifdef AARCH64
+  if (!VM_Version::is_hisi_enabled()) {
+    UsePrimHashMap = false;
+  }
+#else
+  UsePrimHashMap = false;
+#endif
+
   if (log_is_enabled(Info, os, cpu)) {
     char buf[1024];
     ResourceMark rm;
diff --git a/test/jdk/java/util/HashMap/HashMap.java b/test/jdk/java/util/HashMap/HashMap.java
new file mode 100644
index 000000000..4880c2e8f
--- /dev/null
+++ b/test/jdk/java/util/HashMap/HashMap.java
@@ -0,0 +1,3798 @@
+/*
+ * Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.util;
+
+import java.io.IOException;
+import java.io.InvalidObjectException;
+import java.io.ObjectInputStream;
+import java.io.Serializable;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+import java.util.function.BiConsumer;
+import java.util.function.BiFunction;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import jdk.internal.access.SharedSecrets;
+
+/**
+ * Hash table based implementation of the {@code Map} interface.  This
+ * implementation provides all of the optional map operations, and permits
+ * {@code null} values and the {@code null} key.  (The {@code HashMap}
+ * class is roughly equivalent to {@code Hashtable}, except that it is
+ * unsynchronized and permits nulls.)  This class makes no guarantees as to
+ * the order of the map; in particular, it does not guarantee that the order
+ * will remain constant over time.
+ *
+ * <p>This implementation provides constant-time performance for the basic
+ * operations ({@code get} and {@code put}), assuming the hash function
+ * disperses the elements properly among the buckets.  Iteration over
+ * collection views requires time proportional to the "capacity" of the
+ * {@code HashMap} instance (the number of buckets) plus its size (the number
+ * of key-value mappings).  Thus, it's very important not to set the initial
+ * capacity too high (or the load factor too low) if iteration performance is
+ * important.
+ *
+ * <p>An instance of {@code HashMap} has two parameters that affect its
+ * performance: <i>initial capacity</i> and <i>load factor</i>.  The
+ * <i>capacity</i> is the number of buckets in the hash table, and the initial
+ * capacity is simply the capacity at the time the hash table is created.  The
+ * <i>load factor</i> is a measure of how full the hash table is allowed to
+ * get before its capacity is automatically increased.  When the number of
+ * entries in the hash table exceeds the product of the load factor and the
+ * current capacity, the hash table is <i>rehashed</i> (that is, internal data
+ * structures are rebuilt) so that the hash table has approximately twice the
+ * number of buckets.
+ *
+ * <p>As a general rule, the default load factor (.75) offers a good
+ * tradeoff between time and space costs.  Higher values decrease the
+ * space overhead but increase the lookup cost (reflected in most of
+ * the operations of the {@code HashMap} class, including
+ * {@code get} and {@code put}).  The expected number of entries in
+ * the map and its load factor should be taken into account when
+ * setting its initial capacity, so as to minimize the number of
+ * rehash operations.  If the initial capacity is greater than the
+ * maximum number of entries divided by the load factor, no rehash
+ * operations will ever occur.
+ *
+ * <p>If many mappings are to be stored in a {@code HashMap}
+ * instance, creating it with a sufficiently large capacity will allow
+ * the mappings to be stored more efficiently than letting it perform
+ * automatic rehashing as needed to grow the table.  Note that using
+ * many keys with the same {@code hashCode()} is a sure way to slow
+ * down performance of any hash table. To ameliorate impact, when keys
+ * are {@link Comparable}, this class may use comparison order among
+ * keys to help break ties.
+ *
+ * <p><strong>Note that this implementation is not synchronized.</strong>
+ * If multiple threads access a hash map concurrently, and at least one of
+ * the threads modifies the map structurally, it <i>must</i> be
+ * synchronized externally.  (A structural modification is any operation
+ * that adds or deletes one or more mappings; merely changing the value
+ * associated with a key that an instance already contains is not a
+ * structural modification.)  This is typically accomplished by
+ * synchronizing on some object that naturally encapsulates the map.
+ *
+ * If no such object exists, the map should be "wrapped" using the
+ * {@link Collections#synchronizedMap Collections.synchronizedMap}
+ * method.  This is best done at creation time, to prevent accidental
+ * unsynchronized access to the map:<pre>
+ *   Map m = Collections.synchronizedMap(new HashMap(...));</pre>
+ *
+ * <p>The iterators returned by all of this class's "collection view methods"
+ * are <i>fail-fast</i>: if the map is structurally modified at any time after
+ * the iterator is created, in any way except through the iterator's own
+ * {@code remove} method, the iterator will throw a
+ * {@link ConcurrentModificationException}.  Thus, in the face of concurrent
+ * modification, the iterator fails quickly and cleanly, rather than risking
+ * arbitrary, non-deterministic behavior at an undetermined time in the
+ * future.
+ *
+ * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
+ * as it is, generally speaking, impossible to make any hard guarantees in the
+ * presence of unsynchronized concurrent modification.  Fail-fast iterators
+ * throw {@code ConcurrentModificationException} on a best-effort basis.
+ * Therefore, it would be wrong to write a program that depended on this
+ * exception for its correctness: <i>the fail-fast behavior of iterators
+ * should be used only to detect bugs.</i>
+ *
+ * <p>This class is a member of the
+ * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
+ * Java Collections Framework</a>.
+ *
+ * @param <K> the type of keys maintained by this map
+ * @param <V> the type of mapped values
+ *
+ * @author  Doug Lea
+ * @author  Josh Bloch
+ * @author  Arthur van Hoff
+ * @author  Neal Gafter
+ * @see     Object#hashCode()
+ * @see     Collection
+ * @see     Map
+ * @see     TreeMap
+ * @see     Hashtable
+ * @since   1.2
+ */
+public class HashMap<K,V> extends AbstractMap<K,V>
+    implements Map<K,V>, Cloneable, Serializable {
+
+    @java.io.Serial
+    private static final long serialVersionUID = 362498820763181265L;
+
+    /*
+     * Implementation notes.
+     *
+     * This map usually acts as a binned (bucketed) hash table, but
+     * when bins get too large, they are transformed into bins of
+     * TreeNodes, each structured similarly to those in
+     * java.util.TreeMap. Most methods try to use normal bins, but
+     * relay to TreeNode methods when applicable (simply by checking
+     * instanceof a node).  Bins of TreeNodes may be traversed and
+     * used like any others, but additionally support faster lookup
+     * when overpopulated. However, since the vast majority of bins in
+     * normal use are not overpopulated, checking for existence of
+     * tree bins may be delayed in the course of table methods.
+     *
+     * Tree bins (i.e., bins whose elements are all TreeNodes) are
+     * ordered primarily by hashCode, but in the case of ties, if two
+     * elements are of the same "class C implements Comparable<C>",
+     * type then their compareTo method is used for ordering. (We
+     * conservatively check generic types via reflection to validate
+     * this -- see method comparableClassFor).  The added complexity
+     * of tree bins is worthwhile in providing worst-case O(log n)
+     * operations when keys either have distinct hashes or are
+     * orderable, Thus, performance degrades gracefully under
+     * accidental or malicious usages in which hashCode() methods
+     * return values that are poorly distributed, as well as those in
+     * which many keys share a hashCode, so long as they are also
+     * Comparable. (If neither of these apply, we may waste about a
+     * factor of two in time and space compared to taking no
+     * precautions. But the only known cases stem from poor user
+     * programming practices that are already so slow that this makes
+     * little difference.)
+     *
+     * Because TreeNodes are about twice the size of regular nodes, we
+     * use them only when bins contain enough nodes to warrant use
+     * (see TREEIFY_THRESHOLD). And when they become too small (due to
+     * removal or resizing) they are converted back to plain bins.  In
+     * usages with well-distributed user hashCodes, tree bins are
+     * rarely used.  Ideally, under random hashCodes, the frequency of
+     * nodes in bins follows a Poisson distribution
+     * (http://en.wikipedia.org/wiki/Poisson_distribution) with a
+     * parameter of about 0.5 on average for the default resizing
+     * threshold of 0.75, although with a large variance because of
+     * resizing granularity. Ignoring variance, the expected
+     * occurrences of list size k are (exp(-0.5) * pow(0.5, k) /
+     * factorial(k)). The first values are:
+     *
+     * 0:    0.60653066
+     * 1:    0.30326533
+     * 2:    0.07581633
+     * 3:    0.01263606
+     * 4:    0.00157952
+     * 5:    0.00015795
+     * 6:    0.00001316
+     * 7:    0.00000094
+     * 8:    0.00000006
+     * more: less than 1 in ten million
+     *
+     * The root of a tree bin is normally its first node.  However,
+     * sometimes (currently only upon Iterator.remove), the root might
+     * be elsewhere, but can be recovered following parent links
+     * (method TreeNode.root()).
+     *
+     * All applicable internal methods accept a hash code as an
+     * argument (as normally supplied from a public method), allowing
+     * them to call each other without recomputing user hashCodes.
+     * Most internal methods also accept a "tab" argument, that is
+     * normally the current table, but may be a new or old one when
+     * resizing or converting.
+     *
+     * When bin lists are treeified, split, or untreeified, we keep
+     * them in the same relative access/traversal order (i.e., field
+     * Node.next) to better preserve locality, and to slightly
+     * simplify handling of splits and traversals that invoke
+     * iterator.remove. When using comparators on insertion, to keep a
+     * total ordering (or as close as is required here) across
+     * rebalancings, we compare classes and identityHashCodes as
+     * tie-breakers.
+     *
+     * The use and transitions among plain vs tree modes is
+     * complicated by the existence of subclass LinkedHashMap. See
+     * below for hook methods defined to be invoked upon insertion,
+     * removal and access that allow LinkedHashMap internals to
+     * otherwise remain independent of these mechanics. (This also
+     * requires that a map instance be passed to some utility methods
+     * that may create new nodes.)
+     *
+     * The concurrent-programming-like SSA-based coding style helps
+     * avoid aliasing errors amid all of the twisty pointer operations.
+     */
+
+    /**
+     * The default initial capacity - MUST be a power of two.
+     */
+    static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
+
+    /**
+     * The maximum capacity, used if a higher value is implicitly specified
+     * by either of the constructors with arguments.
+     * MUST be a power of two <= 1<<30.
+     */
+    static final int MAXIMUM_CAPACITY = 1 << 30;
+
+    /**
+     * The load factor used when none specified in constructor.
+     */
+    static final float DEFAULT_LOAD_FACTOR = 0.75f;
+
+    /**
+     * The bin count threshold for using a tree rather than list for a
+     * bin.  Bins are converted to trees when adding an element to a
+     * bin with at least this many nodes. The value must be greater
+     * than 2 and should be at least 8 to mesh with assumptions in
+     * tree removal about conversion back to plain bins upon
+     * shrinkage.
+     */
+    static final int TREEIFY_THRESHOLD = 8;
+
+    /**
+     * The bin count threshold for untreeifying a (split) bin during a
+     * resize operation. Should be less than TREEIFY_THRESHOLD, and at
+     * most 6 to mesh with shrinkage detection under removal.
+     */
+    static final int UNTREEIFY_THRESHOLD = 6;
+
+    /**
+     * The smallest table capacity for which bins may be treeified.
+     * (Otherwise the table is resized if too many nodes in a bin.)
+     * Should be at least 4 * TREEIFY_THRESHOLD to avoid conflicts
+     * between resizing and treeification thresholds.
+     */
+    static final int MIN_TREEIFY_CAPACITY = 64;
+
+    /**
+     * The max load factor used for prim long hashmap. The performance of
+     * prim long hashmap will decrease sharply when the value exceeds 0.8f.
+     */
+    static final float MAX_LOAD_FACTOR_FOR_PRIM_MAP = 0.8f;
+
+    static final int NULL_KEY_INDEX_FOR_RPIM_MAP = -1;
+    static final int KEY_NO_EXIST_FOR_PRIM_MAP = -2;
+
+    /**
+     * Basic hash bin node, used for most entries.  (See below for
+     * TreeNode subclass, and in LinkedHashMap for its Entry subclass.)
+     */
+    static class Node<K,V> implements Map.Entry<K,V> {
+        final int hash;
+        final K key;
+        V value;
+        Node<K,V> next;
+
+        Node(int hash, K key, V value, Node<K,V> next) {
+            this.hash = hash;
+            this.key = key;
+            this.value = value;
+            this.next = next;
+        }
+
+        public final K getKey()        { return key; }
+        public final V getValue()      { return value; }
+        public final String toString() { return key + "=" + value; }
+
+        public final int hashCode() {
+            return Objects.hashCode(key) ^ Objects.hashCode(value);
+        }
+
+        public final V setValue(V newValue) {
+            V oldValue = value;
+            value = newValue;
+            return oldValue;
+        }
+
+        public final boolean equals(Object o) {
+            if (o == this)
+                return true;
+
+            return o instanceof Map.Entry<?, ?> e
+                    && Objects.equals(key, e.getKey())
+                    && Objects.equals(value, e.getValue());
+        }
+    }
+
+    /* ---------------- Static utilities -------------- */
+
+    /**
+     * Computes key.hashCode() and spreads (XORs) higher bits of hash
+     * to lower.  Because the table uses power-of-two masking, sets of
+     * hashes that vary only in bits above the current mask will
+     * always collide. (Among known examples are sets of Float keys
+     * holding consecutive whole numbers in small tables.)  So we
+     * apply a transform that spreads the impact of higher bits
+     * downward. There is a tradeoff between speed, utility, and
+     * quality of bit-spreading. Because many common sets of hashes
+     * are already reasonably distributed (so don't benefit from
+     * spreading), and because we use trees to handle large sets of
+     * collisions in bins, we just XOR some shifted bits in the
+     * cheapest possible way to reduce systematic lossage, as well as
+     * to incorporate impact of the highest bits that would otherwise
+     * never be used in index calculations because of table bounds.
+     */
+    static final int hash(Object key) {
+        int h;
+        return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
+    }
+
+    /**
+     * Returns x's Class if it is of the form "class C implements
+     * Comparable<C>", else null.
+     */
+    static Class<?> comparableClassFor(Object x) {
+        if (x instanceof Comparable) {
+            Class<?> c; Type[] ts, as; ParameterizedType p;
+            if ((c = x.getClass()) == String.class) // bypass checks
+                return c;
+            if ((ts = c.getGenericInterfaces()) != null) {
+                for (Type t : ts) {
+                    if ((t instanceof ParameterizedType) &&
+                        ((p = (ParameterizedType) t).getRawType() ==
+                         Comparable.class) &&
+                        (as = p.getActualTypeArguments()) != null &&
+                        as.length == 1 && as[0] == c) // type arg is c
+                        return c;
+                }
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Returns k.compareTo(x) if x matches kc (k's screened comparable
+     * class), else 0.
+     */
+    @SuppressWarnings({"rawtypes","unchecked"}) // for cast to Comparable
+    static int compareComparables(Class<?> kc, Object k, Object x) {
+        return (x == null || x.getClass() != kc ? 0 :
+                ((Comparable)k).compareTo(x));
+    }
+
+    /**
+     * Returns a power of two size for the given target capacity.
+     */
+    static final int tableSizeFor(int cap) {
+        int n = -1 >>> Integer.numberOfLeadingZeros(cap - 1);
+        return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
+    }
+
+    /* ---------------- Fields -------------- */
+
+    /**
+     * The table, initialized on first use, and resized as
+     * necessary. When allocated, length is always a power of two.
+     * (We also tolerate length zero in some operations to allow
+     * bootstrapping mechanics that are currently not needed.)
+     */
+    transient Node<K,V>[] table;
+
+    /**
+     * Holds cached entrySet(). Note that AbstractMap fields are used
+     * for keySet() and values().
+     */
+    transient Set<Map.Entry<K,V>> entrySet;
+
+    /**
+     * The number of key-value mappings contained in this map.
+     */
+    transient int size;
+
+    /**
+     * The number of times this HashMap has been structurally modified
+     * Structural modifications are those that change the number of mappings in
+     * the HashMap or otherwise modify its internal structure (e.g.,
+     * rehash).  This field is used to make iterators on Collection-views of
+     * the HashMap fail-fast.  (See ConcurrentModificationException).
+     */
+    transient int modCount;
+
+    /**
+     * The next size value at which to resize (capacity * load factor).
+     *
+     * @serial
+     */
+    // (The javadoc description is true upon serialization.
+    // Additionally, if the table array has not been allocated, this
+    // field holds the initial array capacity, or zero signifying
+    // DEFAULT_INITIAL_CAPACITY.)
+    int threshold;
+
+    /**
+     * The load factor for the hash table.
+     *
+     * @serial
+     */
+    final float loadFactor;
+
+    /**
+     * The keys in prim long hashmap.
+     */
+    transient Long[] primMapKeys;
+
+    /**
+     * The values in prim long hashmap.
+     */
+    transient V[] primMapValues;
+
+    /**
+     * Indicates whether the element is valid in prim long hashmap.
+     */
+    transient boolean[] primMapValids;
+
+    /**
+     * The value of null key in prim long hashmap.
+     */
+    transient V primMapValOfNullKey;
+
+    /**
+     * Indicates whether null key exist in prim long hashmap.
+     */
+    transient boolean primMapNullKeyValid;
+
+    /**
+     * Indicates whether the current state is in prim long map.
+     */
+    transient boolean usingPrimHashMap;
+
+    /* ---------------- Public operations -------------- */
+
+    /**
+     * Constructs an empty {@code HashMap} with the specified initial
+     * capacity and load factor.
+     *
+     * @param  initialCapacity the initial capacity
+     * @param  loadFactor      the load factor
+     * @throws IllegalArgumentException if the initial capacity is negative
+     *         or the load factor is nonpositive
+     */
+    public HashMap(int initialCapacity, float loadFactor) {
+        if (initialCapacity < 0)
+            throw new IllegalArgumentException("Illegal initial capacity: " +
+                                               initialCapacity);
+        if (initialCapacity > MAXIMUM_CAPACITY)
+            initialCapacity = MAXIMUM_CAPACITY;
+        if (loadFactor <= 0 || Float.isNaN(loadFactor))
+            throw new IllegalArgumentException("Illegal load factor: " +
+                                               loadFactor);
+        this.loadFactor = loadFactor;
+        this.threshold = tableSizeFor(initialCapacity);
+        if (this.loadFactor > MAX_LOAD_FACTOR_FOR_PRIM_MAP) {
+            disablePrimHashMap();
+        } else {
+            initUsingPrimHashMap();
+        }
+    }
+
+    /**
+     * Constructs an empty {@code HashMap} with the specified initial
+     * capacity and the default load factor (0.75).
+     *
+     * @param  initialCapacity the initial capacity.
+     * @throws IllegalArgumentException if the initial capacity is negative.
+     */
+    public HashMap(int initialCapacity) {
+        this(initialCapacity, DEFAULT_LOAD_FACTOR);
+    }
+
+    /**
+     * Constructs an empty {@code HashMap} with the default initial capacity
+     * (16) and the default load factor (0.75).
+     */
+    public HashMap() {
+        initUsingPrimHashMap();
+        this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
+    }
+
+    /**
+     * Constructs a new {@code HashMap} with the same mappings as the
+     * specified {@code Map}.  The {@code HashMap} is created with
+     * default load factor (0.75) and an initial capacity sufficient to
+     * hold the mappings in the specified {@code Map}.
+     *
+     * @param   m the map whose mappings are to be placed in this map
+     * @throws  NullPointerException if the specified map is null
+     */
+    public HashMap(Map<? extends K, ? extends V> m) {
+        initUsingPrimHashMap();
+        this.loadFactor = DEFAULT_LOAD_FACTOR;
+        putMapEntries(m, false);
+    }
+
+    /**
+     * Implements Map.putAll and Map constructor.
+     *
+     * @param m the map
+     * @param evict false when initially constructing this map, else
+     * true (relayed to method afterNodeInsertion).
+     */
+    final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict) {
+        int s = m.size();
+        if (s > 0) {
+            if ((!usePrimHashMap() && table == null) ||
+                (usePrimHashMap() && primMapValids == null)) { // pre-size
+                float ft = ((float)s / loadFactor) + 1.0F;
+                int t = ((ft < (float)MAXIMUM_CAPACITY) ?
+                         (int)ft : MAXIMUM_CAPACITY);
+                if (t > threshold)
+                    threshold = tableSizeFor(t);
+            } else {
+                if (!usePrimHashMap()) {
+                    // Because of linked-list bucket constraints, we cannot
+                    // expand all at once, but can reduce total resize
+                    // effort by repeated doubling now vs later
+                    while (s > threshold && table.length < MAXIMUM_CAPACITY)
+                        resize();
+                } else {
+                    while (s > threshold && primMapValids.length < MAXIMUM_CAPACITY)
+                        primHashMapResize();
+                }
+            }
+
+            for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
+                K key = e.getKey();
+                V value = e.getValue();
+                if (!usePrimHashMap(key)) {
+                    putVal(key, value, false, evict, true);
+                } else {
+                    primHashMapPutVal((Long)key, value, false);
+                }
+            }
+        }
+    }
+
+    /**
+     * Returns the number of key-value mappings in this map.
+     *
+     * @return the number of key-value mappings in this map
+     */
+    public int size() {
+        return size;
+    }
+
+    /**
+     * Returns {@code true} if this map contains no key-value mappings.
+     *
+     * @return {@code true} if this map contains no key-value mappings
+     */
+    public boolean isEmpty() {
+        return size == 0;
+    }
+
+    /**
+     * Returns the value to which the specified key is mapped,
+     * or {@code null} if this map contains no mapping for the key.
+     *
+     * <p>More formally, if this map contains a mapping from a key
+     * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
+     * key.equals(k))}, then this method returns {@code v}; otherwise
+     * it returns {@code null}.  (There can be at most one such mapping.)
+     *
+     * <p>A return value of {@code null} does not <i>necessarily</i>
+     * indicate that the map contains no mapping for the key; it's also
+     * possible that the map explicitly maps the key to {@code null}.
+     * The {@link #containsKey containsKey} operation may be used to
+     * distinguish these two cases.
+     *
+     * @see #put(Object, Object)
+     */
+    public V get(Object key) {
+        if (usePrimHashMap()) {
+            return primHashMapGet(key);
+        }
+        Node<K,V> e;
+        return (e = getNode(key)) == null ? null : e.value;
+    }
+
+    /**
+     * Implements Map.get and related methods.
+     *
+     * @param key the key
+     * @return the node, or null if none
+     */
+    final Node<K,V> getNode(Object key) {
+        Node<K,V>[] tab; Node<K,V> first, e; int n, hash; K k;
+        if ((tab = table) != null && (n = tab.length) > 0 &&
+            (first = tab[(n - 1) & (hash = hash(key))]) != null) {
+            if (first.hash == hash && // always check first node
+                ((k = first.key) == key || (key != null && key.equals(k))))
+                return first;
+            if ((e = first.next) != null) {
+                if (first instanceof TreeNode)
+                    return ((TreeNode<K,V>)first).getTreeNode(hash, key);
+                do {
+                    if (e.hash == hash &&
+                        ((k = e.key) == key || (key != null && key.equals(k))))
+                        return e;
+                } while ((e = e.next) != null);
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Returns {@code true} if this map contains a mapping for the
+     * specified key.
+     *
+     * @param   key   The key whose presence in this map is to be tested
+     * @return {@code true} if this map contains a mapping for the specified
+     * key.
+     */
+    public boolean containsKey(Object key) {
+        if (usePrimHashMap()) {
+            return (primHashGetIndexByKey(key) != KEY_NO_EXIST_FOR_PRIM_MAP);
+        }
+        return getNode(key) != null;
+    }
+
+    /**
+     * Associates the specified value with the specified key in this map.
+     * If the map previously contained a mapping for the key, the old
+     * value is replaced.
+     *
+     * @param key key with which the specified value is to be associated
+     * @param value value to be associated with the specified key
+     * @return the previous value associated with {@code key}, or
+     *         {@code null} if there was no mapping for {@code key}.
+     *         (A {@code null} return can also indicate that the map
+     *         previously associated {@code null} with {@code key}.)
+     */
+    public V put(K key, V value) {
+        if (usePrimHashMap(key)) {
+            return primHashMapPutVal((Long)key, value, false);
+        }
+        return putVal(key, value, false, true, true);
+    }
+
+    /**
+     * Implements Map.put and related methods.
+     *
+     * @param key the key
+     * @param value the value to put
+     * @param onlyIfAbsent if true, don't change existing value
+     * @param evict if false, the table is in creation mode.
+     * @param update if false(in rollback state), don't update size and modcount
+     * @return previous value, or null if none
+     */
+    final V putVal(K key, V value, boolean onlyIfAbsent,
+                   boolean evict, boolean update) {
+        int hash = hash(key);
+        Node<K,V>[] tab; Node<K,V> p; int n, i;
+        if ((tab = table) == null || (n = tab.length) == 0)
+            n = (tab = resize()).length;
+        if ((p = tab[i = (n - 1) & hash]) == null)
+            tab[i] = newNode(hash, key, value, null);
+        else {
+            Node<K,V> e; K k;
+            if (p.hash == hash &&
+                ((k = p.key) == key || (key != null && key.equals(k))))
+                e = p;
+            else if (p instanceof TreeNode)
+                e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
+            else {
+                for (int binCount = 0; ; ++binCount) {
+                    if ((e = p.next) == null) {
+                        p.next = newNode(hash, key, value, null);
+                        if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
+                            treeifyBin(tab, hash);
+                        break;
+                    }
+                    if (e.hash == hash &&
+                        ((k = e.key) == key || (key != null && key.equals(k))))
+                        break;
+                    p = e;
+                }
+            }
+            if (e != null) { // existing mapping for key
+                V oldValue = e.value;
+                if (!onlyIfAbsent || oldValue == null)
+                    e.value = value;
+                afterNodeAccess(e);
+                return oldValue;
+            }
+        }
+        if (update) {
+            ++modCount;
+            if (++size > threshold)
+                resize();
+        }
+        afterNodeInsertion(evict);
+        return null;
+    }
+
+    /**
+     * Calculate the new capacity based on the old capacity.
+     * If the old value is 0, the new capacity is set to the
+     * initial capacity saved in the threshold field.
+     * Otherwise, set the new capacity to double the old capacity.
+     * This method update threshold at the same time.
+     *
+     * @return the new capacity. 0 if oldCap reaches the max capacity.
+     */
+    private int calNewCapAndUpdateThreshold(int oldCap) {
+        int oldThr = threshold;
+        int newCap, newThr = 0;
+        if (oldCap > 0) {
+            if (oldCap >= MAXIMUM_CAPACITY) {
+                threshold = Integer.MAX_VALUE;
+                return 0;
+            }
+            else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
+                     oldCap >= DEFAULT_INITIAL_CAPACITY)
+                newThr = oldThr << 1; // double threshold
+        }
+        else if (oldThr > 0) // initial capacity was placed in threshold
+            newCap = oldThr;
+        else {               // zero initial threshold signifies using defaults
+            newCap = DEFAULT_INITIAL_CAPACITY;
+            newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
+        }
+        if (newThr == 0) {
+            float ft = (float)newCap * loadFactor;
+            newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
+                      (int)ft : Integer.MAX_VALUE);
+        }
+        threshold = newThr;
+        return newCap;
+    }
+
+    /**
+     * Initializes or doubles table size.  If null, allocates in
+     * accord with initial capacity target held in field threshold.
+     * Otherwise, because we are using power-of-two expansion, the
+     * elements from each bin must either stay at same index, or move
+     * with a power of two offset in the new table.
+     *
+     * @return the table
+     */
+    final Node<K,V>[] resize() {
+        Node<K,V>[] oldTab = table;
+        final int oldCap = (oldTab == null) ? 0 : oldTab.length;
+        int newCap = calNewCapAndUpdateThreshold(oldCap);
+        // 0 means oldCap reaches the MAXIMUM_CAPACITY
+        if (newCap == 0) {
+            return oldTab;
+        }
+        @SuppressWarnings({"rawtypes","unchecked"})
+        Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
+        table = newTab;
+        if (oldTab != null) {
+            for (int j = 0; j < oldCap; ++j) {
+                Node<K,V> e;
+                if ((e = oldTab[j]) != null) {
+                    oldTab[j] = null;
+                    if (e.next == null)
+                        newTab[e.hash & (newCap - 1)] = e;
+                    else if (e instanceof TreeNode)
+                        ((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
+                    else { // preserve order
+                        Node<K,V> loHead = null, loTail = null;
+                        Node<K,V> hiHead = null, hiTail = null;
+                        Node<K,V> next;
+                        do {
+                            next = e.next;
+                            if ((e.hash & oldCap) == 0) {
+                                if (loTail == null)
+                                    loHead = e;
+                                else
+                                    loTail.next = e;
+                                loTail = e;
+                            }
+                            else {
+                                if (hiTail == null)
+                                    hiHead = e;
+                                else
+                                    hiTail.next = e;
+                                hiTail = e;
+                            }
+                        } while ((e = next) != null);
+                        if (loTail != null) {
+                            loTail.next = null;
+                            newTab[j] = loHead;
+                        }
+                        if (hiTail != null) {
+                            hiTail.next = null;
+                            newTab[j + oldCap] = hiHead;
+                        }
+                    }
+                }
+            }
+        }
+        return newTab;
+    }
+
+    /**
+     * Replaces all linked nodes in bin at index for given hash unless
+     * table is too small, in which case resizes instead.
+     */
+    final void treeifyBin(Node<K,V>[] tab, int hash) {
+        int n, index; Node<K,V> e;
+        if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
+            resize();
+        else if ((e = tab[index = (n - 1) & hash]) != null) {
+            TreeNode<K,V> hd = null, tl = null;
+            do {
+                TreeNode<K,V> p = replacementTreeNode(e, null);
+                if (tl == null)
+                    hd = p;
+                else {
+                    p.prev = tl;
+                    tl.next = p;
+                }
+                tl = p;
+            } while ((e = e.next) != null);
+            if ((tab[index] = hd) != null)
+                hd.treeify(tab);
+        }
+    }
+
+    /**
+     * Copies all of the mappings from the specified map to this map.
+     * These mappings will replace any mappings that this map had for
+     * any of the keys currently in the specified map.
+     *
+     * @param m mappings to be stored in this map
+     * @throws NullPointerException if the specified map is null
+     */
+    public void putAll(Map<? extends K, ? extends V> m) {
+        putMapEntries(m, true);
+    }
+
+    /**
+     * Removes the mapping for the specified key from this map if present.
+     *
+     * @param  key key whose mapping is to be removed from the map
+     * @return the previous value associated with {@code key}, or
+     *         {@code null} if there was no mapping for {@code key}.
+     *         (A {@code null} return can also indicate that the map
+     *         previously associated {@code null} with {@code key}.)
+     */
+    public V remove(Object key) {
+        if (usePrimHashMap(key)) {
+            return primHashMapRemoveByKey(key);
+        }
+        Node<K,V> e;
+        return (e = removeNode(hash(key), key, null, false, true)) == null ?
+            null : e.value;
+    }
+
+    /**
+     * Implements Map.remove and related methods.
+     *
+     * @param hash hash for key
+     * @param key the key
+     * @param value the value to match if matchValue, else ignored
+     * @param matchValue if true only remove if value is equal
+     * @param movable if false do not move other nodes while removing
+     * @return the node, or null if none
+     */
+    final Node<K,V> removeNode(int hash, Object key, Object value,
+                               boolean matchValue, boolean movable) {
+        Node<K,V>[] tab; Node<K,V> p; int n, index;
+        if ((tab = table) != null && (n = tab.length) > 0 &&
+            (p = tab[index = (n - 1) & hash]) != null) {
+            Node<K,V> node = null, e; K k; V v;
+            if (p.hash == hash &&
+                ((k = p.key) == key || (key != null && key.equals(k))))
+                node = p;
+            else if ((e = p.next) != null) {
+                if (p instanceof TreeNode)
+                    node = ((TreeNode<K,V>)p).getTreeNode(hash, key);
+                else {
+                    do {
+                        if (e.hash == hash &&
+                            ((k = e.key) == key ||
+                             (key != null && key.equals(k)))) {
+                            node = e;
+                            break;
+                        }
+                        p = e;
+                    } while ((e = e.next) != null);
+                }
+            }
+            if (node != null && (!matchValue || (v = node.value) == value ||
+                                 (value != null && value.equals(v)))) {
+                if (node instanceof TreeNode)
+                    ((TreeNode<K,V>)node).removeTreeNode(this, tab, movable);
+                else if (node == p)
+                    tab[index] = node.next;
+                else
+                    p.next = node.next;
+                ++modCount;
+                --size;
+                afterNodeRemoval(node);
+                return node;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Removes all of the mappings from this map.
+     * The map will be empty after this call returns.
+     */
+    public void clear() {
+        modCount++;
+        if (usePrimHashMap()) {
+            if (size > 0) {
+                size = 0;
+                if (primMapValids != null && primMapValids.length != 0) {
+                    Arrays.fill(primMapValids, false);
+                    Arrays.fill(primMapValues, null);
+                }
+                primMapNullKeyValid = false;
+                primMapValOfNullKey = null;
+            }
+        } else {
+            Node<K,V>[] tab;
+            if ((tab = table) != null && size > 0) {
+                size = 0;
+                for (int i = 0; i < tab.length; ++i)
+                    tab[i] = null;
+            }
+        }
+    }
+
+    /**
+     * Returns {@code true} if this map maps one or more keys to the
+     * specified value.
+     *
+     * @param value value whose presence in this map is to be tested
+     * @return {@code true} if this map maps one or more keys to the
+     *         specified value
+     */
+    public boolean containsValue(Object value) {
+        if (usePrimHashMap()) {
+            return primHashMapContainsValue(value);
+        }
+        Node<K,V>[] tab; V v;
+        if ((tab = table) != null && size > 0) {
+            for (Node<K,V> e : tab) {
+                for (; e != null; e = e.next) {
+                    if ((v = e.value) == value ||
+                        (value != null && value.equals(v)))
+                        return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Returns a {@link Set} view of the keys contained in this map.
+     * The set is backed by the map, so changes to the map are
+     * reflected in the set, and vice-versa.  If the map is modified
+     * while an iteration over the set is in progress (except through
+     * the iterator's own {@code remove} operation), the results of
+     * the iteration are undefined.  The set supports element removal,
+     * which removes the corresponding mapping from the map, via the
+     * {@code Iterator.remove}, {@code Set.remove},
+     * {@code removeAll}, {@code retainAll}, and {@code clear}
+     * operations.  It does not support the {@code add} or {@code addAll}
+     * operations.
+     *
+     * @return a set view of the keys contained in this map
+     */
+    public Set<K> keySet() {
+        Set<K> ks = keySet;
+        if (ks == null) {
+            ks = new KeySet();
+            keySet = ks;
+        }
+        return ks;
+    }
+
+    /**
+     * Prepares the array for {@link Collection#toArray(Object[])} implementation.
+     * If supplied array is smaller than this map size, a new array is allocated.
+     * If supplied array is bigger than this map size, a null is written at size index.
+     *
+     * @param a an original array passed to {@code toArray()} method
+     * @param <T> type of array elements
+     * @return an array ready to be filled and returned from {@code toArray()} method.
+     */
+    @SuppressWarnings("unchecked")
+    final <T> T[] prepareArray(T[] a) {
+        int size = this.size;
+        if (a.length < size) {
+            return (T[]) java.lang.reflect.Array
+                    .newInstance(a.getClass().getComponentType(), size);
+        }
+        if (a.length > size) {
+            a[size] = null;
+        }
+        return a;
+    }
+
+    /**
+     * Fills an array with this map keys and returns it. This method assumes
+     * that input array is big enough to fit all the keys. Use
+     * {@link #prepareArray(Object[])} to ensure this.
+     *
+     * @param a an array to fill
+     * @param <T> type of array elements
+     * @return supplied array
+     */
+    <T> T[] keysToArray(T[] a) {
+        Object[] r = a;
+        int idx = 0;
+        if (usePrimHashMap()) {
+            int remaining = size;
+            if (primMapNullKeyValid) {
+                r[idx++] = null;
+                --remaining;
+            }
+            if (remaining > 0) {
+                boolean[] valids = primMapValids;
+                Long[] keys = primMapKeys;
+                int length = valids.length;
+                for (int i = 0; remaining > 0 && i < length; ++i) {
+                    if (valids[i]) {
+                        r[idx++] = keys[i];
+                        --remaining;
+                    }
+                }
+            }
+        } else {
+            Node<K,V>[] tab;
+            if (size > 0 && (tab = table) != null) {
+                for (Node<K,V> e : tab) {
+                    for (; e != null; e = e.next) {
+                        r[idx++] = e.key;
+                    }
+                }
+            }
+        }
+        return a;
+    }
+
+    /**
+     * Fills an array with this map values and returns it. This method assumes
+     * that input array is big enough to fit all the values. Use
+     * {@link #prepareArray(Object[])} to ensure this.
+     *
+     * @param a an array to fill
+     * @param <T> type of array elements
+     * @return supplied array
+     */
+    <T> T[] valuesToArray(T[] a) {
+        Object[] r = a;
+        int idx = 0;
+        if (usePrimHashMap()) {
+            int remaining = size;
+            if (primMapNullKeyValid) {
+                r[idx++] = primMapValOfNullKey;
+                --remaining;
+            }
+            if (remaining > 0) {
+                boolean[] valids = primMapValids;
+                V[] values = primMapValues;
+                int length = valids.length;
+                for (int i = 0; remaining > 0 && i < length; ++i) {
+                    if (valids[i]) {
+                        r[idx++] = values[i];
+                        --remaining;
+                    }
+                }
+            }
+        } else {
+            Node<K,V>[] tab;
+            if (size > 0 && (tab = table) != null) {
+                for (Node<K,V> e : tab) {
+                    for (; e != null; e = e.next) {
+                        r[idx++] = e.value;
+                    }
+                }
+            }
+        }
+        return a;
+    }
+
+    final class KeySet extends AbstractSet<K> {
+        public final int size()                 { return size; }
+        public final void clear()               { HashMap.this.clear(); }
+        public final Iterator<K> iterator()     {
+            if (usePrimHashMap()) {
+                return new primHashMapKeyIterator();
+            }
+            return new KeyIterator();
+        }
+        public final boolean contains(Object o) { return containsKey(o); }
+        public final boolean remove(Object key) {
+            if (usePrimHashMap(key)) {
+                int index = primHashGetIndexByKey(key);
+                if (index == KEY_NO_EXIST_FOR_PRIM_MAP) {
+                    return false;
+                }
+                primHashMapRemoveByIndex(index);
+                return true;
+            }
+            return removeNode(hash(key), key, null, false, true) != null;
+        }
+        public final Spliterator<K> spliterator() {
+            if (usePrimHashMap()) {
+                return new primHashMapKeySpliterator(0, -1, 0, 0, primMapNullKeyValid);
+            }
+            return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0);
+        }
+
+        public Object[] toArray() {
+            return keysToArray(new Object[size]);
+        }
+
+        public <T> T[] toArray(T[] a) {
+            return keysToArray(prepareArray(a));
+        }
+
+        public final void forEach(Consumer<? super K> action) {
+            int mc = modCount;
+            if (action == null)
+                throw new NullPointerException();
+            if (usePrimHashMap()) {
+                int remaining = size;
+                if (primMapNullKeyValid) {
+                    action.accept(null);
+                    --remaining;
+                }
+                if (remaining > 0) {
+                    boolean[] valids = primMapValids;
+                    Long[] keys = primMapKeys;
+                    int length = valids.length;
+                    for (int i = 0; remaining > 0 && i < length; ++i) {
+                        if (valids[i]) {
+                            action.accept(castKeyToGenericType(keys[i]));
+                            --remaining;
+                        }
+                    }
+                }
+            } else {
+                Node<K,V>[] tab;
+                if (size > 0 && (tab = table) != null) {
+                    for (Node<K,V> e : tab) {
+                        for (; e != null; e = e.next)
+                            action.accept(e.key);
+                    }
+                }
+            }
+            if (modCount != mc)
+                throw new ConcurrentModificationException();
+        }
+    }
+
+    /**
+     * Returns a {@link Collection} view of the values contained in this map.
+     * The collection is backed by the map, so changes to the map are
+     * reflected in the collection, and vice-versa.  If the map is
+     * modified while an iteration over the collection is in progress
+     * (except through the iterator's own {@code remove} operation),
+     * the results of the iteration are undefined.  The collection
+     * supports element removal, which removes the corresponding
+     * mapping from the map, via the {@code Iterator.remove},
+     * {@code Collection.remove}, {@code removeAll},
+     * {@code retainAll} and {@code clear} operations.  It does not
+     * support the {@code add} or {@code addAll} operations.
+     *
+     * @return a view of the values contained in this map
+     */
+    public Collection<V> values() {
+        Collection<V> vs = values;
+        if (vs == null) {
+            vs = new Values();
+            values = vs;
+        }
+        return vs;
+    }
+
+    final class Values extends AbstractCollection<V> {
+        public final int size()                 { return size; }
+        public final void clear()               { HashMap.this.clear(); }
+        public final Iterator<V> iterator()     {
+            if (usePrimHashMap()) {
+                return new primHashMapValueIterator();
+            }
+            return new ValueIterator();
+        }
+        public final boolean contains(Object o) { return containsValue(o); }
+        public final Spliterator<V> spliterator() {
+            if (usePrimHashMap()) {
+                return new primHashMapValueSpliterator(0, -1, 0, 0, primMapNullKeyValid);
+            }
+            return new ValueSpliterator<>(HashMap.this, 0, -1, 0, 0);
+        }
+
+        public Object[] toArray() {
+            return valuesToArray(new Object[size]);
+        }
+
+        public <T> T[] toArray(T[] a) {
+            return valuesToArray(prepareArray(a));
+        }
+
+        public final void forEach(Consumer<? super V> action) {
+            if (action == null)
+                throw new NullPointerException();
+            int mc = modCount;
+            if (usePrimHashMap()) {
+                int remaining = size;
+                if (primMapNullKeyValid) {
+                    action.accept(primMapValOfNullKey);
+                    --remaining;
+                }
+                if (remaining > 0) {
+                    boolean[] valids = primMapValids;
+                    V[] values = primMapValues;
+                    int length = valids.length;
+                    for (int i = 0; remaining > 0 && i < length; ++i) {
+                        if (valids[i]) {
+                            action.accept(values[i]);
+                            --remaining;
+                        }
+                    }
+                }
+            } else {
+                Node<K,V>[] tab;
+                if (size > 0 && (tab = table) != null) {
+                    for (Node<K,V> e : tab) {
+                        for (; e != null; e = e.next)
+                            action.accept(e.value);
+                    }
+                }
+            }
+            if (modCount != mc)
+                throw new ConcurrentModificationException();
+        }
+    }
+
+    /**
+     * Returns a {@link Set} view of the mappings contained in this map.
+     * The set is backed by the map, so changes to the map are
+     * reflected in the set, and vice-versa.  If the map is modified
+     * while an iteration over the set is in progress (except through
+     * the iterator's own {@code remove} operation, or through the
+     * {@code setValue} operation on a map entry returned by the
+     * iterator) the results of the iteration are undefined.  The set
+     * supports element removal, which removes the corresponding
+     * mapping from the map, via the {@code Iterator.remove},
+     * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
+     * {@code clear} operations.  It does not support the
+     * {@code add} or {@code addAll} operations.
+     *
+     * @return a set view of the mappings contained in this map
+     */
+    public Set<Map.Entry<K,V>> entrySet() {
+        Set<Map.Entry<K,V>> es;
+        return (es = entrySet) == null ? (entrySet = new EntrySet()) : es;
+    }
+
+    final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
+        public final int size()                 { return size; }
+        public final void clear()               { HashMap.this.clear(); }
+        public final Iterator<Map.Entry<K,V>> iterator() {
+            if (usePrimHashMap()) {
+                return new primHashMapEntryIterator();
+            }
+            return new EntryIterator();
+        }
+        public final boolean contains(Object o) {
+            if (!(o instanceof Map.Entry<?, ?> e))
+                return false;
+            Object key = e.getKey();
+            if (usePrimHashMap()) {
+                int index = primHashGetIndexByKey(key);
+                if (index == KEY_NO_EXIST_FOR_PRIM_MAP) {
+                    return false;
+                }
+                Object value = e.getValue();
+                return (index == NULL_KEY_INDEX_FOR_RPIM_MAP) ?
+                        Objects.equals(value, primMapValOfNullKey) :
+                        Objects.equals(value, primMapValues[index]);
+            } else {
+                Node<K,V> candidate = getNode(key);
+                return candidate != null && candidate.equals(e);
+            }
+        }
+        public final boolean remove(Object o) {
+            if (o instanceof Map.Entry<?, ?> e) {
+                Object key = e.getKey();
+                Object value = e.getValue();
+                return HashMap.this.remove(key, value);
+            }
+            return false;
+        }
+        public final Spliterator<Map.Entry<K,V>> spliterator() {
+            if (usePrimHashMap()) {
+                return new primHashMapEntrySpliterator(0, -1, 0, 0, primMapNullKeyValid);
+            }
+            return new EntrySpliterator<>(HashMap.this, 0, -1, 0, 0);
+        }
+        public final void forEach(Consumer<? super Map.Entry<K,V>> action) {
+            if (action == null)
+                throw new NullPointerException();
+            if (usePrimHashMap()) {
+                Iterator<Map.Entry<K,V>> iter = iterator();
+                int mc = modCount;
+                while (iter.hasNext()) {
+                    Map.Entry<K,V> e = iter.next();
+                    action.accept(e);
+                }
+                if (modCount != mc)
+                    throw new ConcurrentModificationException();
+            }
+            else {
+                Node<K,V>[] tab;
+                if (size > 0 && (tab = table) != null) {
+                    int mc = modCount;
+                    for (Node<K,V> e : tab) {
+                        for (; e != null; e = e.next)
+                            action.accept(e);
+                    }
+                    if (modCount != mc)
+                        throw new ConcurrentModificationException();
+                }
+            }
+        }
+    }
+
+    // Overrides of JDK8 Map extension methods
+
+    @Override
+    public V getOrDefault(Object key, V defaultValue) {
+        if (usePrimHashMap()) {
+            int index = primHashGetIndexByKey(key);
+            if (index == KEY_NO_EXIST_FOR_PRIM_MAP) {
+                return defaultValue;
+            }
+            return primHashMapGetValByIndex(index);
+        }
+        Node<K,V> e;
+        return (e = getNode(key)) == null ? defaultValue : e.value;
+    }
+
+    @Override
+    public V putIfAbsent(K key, V value) {
+        if (usePrimHashMap(key)) {
+            return primHashMapPutVal((Long)key, value, true);
+        }
+        return putVal(key, value, true, true, true);
+    }
+
+    @Override
+    public boolean remove(Object key, Object value) {
+        if (usePrimHashMap(key)) {
+            int index = primHashGetIndexByKey(key);
+            if (index == KEY_NO_EXIST_FOR_PRIM_MAP) {
+                return false;
+            }
+            Object val = primHashMapGetValByIndex(index);
+            if (Objects.equals(value, val)) {
+                primHashMapRemoveByIndex(index);
+                return true;
+            }
+            return false;
+        }
+        return removeNode(hash(key), key, value, true, true) != null;
+    }
+
+    @Override
+    public boolean replace(K key, V oldValue, V newValue) {
+        if (usePrimHashMap(key)) {
+            int index = primHashGetIndexByKey(key);
+            if (index == KEY_NO_EXIST_FOR_PRIM_MAP) {
+                return false;
+            }
+            if (index == NULL_KEY_INDEX_FOR_RPIM_MAP) {
+                if (Objects.equals(oldValue, primMapValOfNullKey)) {
+                    primMapValOfNullKey = newValue;
+                    return true;
+                }
+            } else {
+                if (Objects.equals(oldValue, primMapValues[index])) {
+                    primMapValues[index] = newValue;
+                    return true;
+                }
+            }
+            return false;
+        }
+        Node<K,V> e; V v;
+        if ((e = getNode(key)) != null &&
+            ((v = e.value) == oldValue || (v != null && v.equals(oldValue)))) {
+            e.value = newValue;
+            afterNodeAccess(e);
+            return true;
+        }
+        return false;
+    }
+
+    @Override
+    public V replace(K key, V value) {
+        if (usePrimHashMap(key)) {
+            int index = primHashGetIndexByKey(key);
+            if (index == KEY_NO_EXIST_FOR_PRIM_MAP) {
+                return null;
+            }
+            V oldValue;
+            if (index == NULL_KEY_INDEX_FOR_RPIM_MAP) {
+                oldValue = primMapValOfNullKey;
+                primMapValOfNullKey = value;
+            } else {
+                oldValue = primMapValues[index];
+                primMapValues[index] = value;
+            }
+            return oldValue;
+        }
+        Node<K,V> e;
+        if ((e = getNode(key)) != null) {
+            V oldValue = e.value;
+            e.value = value;
+            afterNodeAccess(e);
+            return oldValue;
+        }
+        return null;
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * <p>This method will, on a best-effort basis, throw a
+     * {@link ConcurrentModificationException} if it is detected that the
+     * mapping function modifies this map during computation.
+     *
+     * @throws ConcurrentModificationException if it is detected that the
+     * mapping function modified this map
+     */
+    @Override
+    public V computeIfAbsent(K key,
+                             Function<? super K, ? extends V> mappingFunction) {
+        if (mappingFunction == null)
+            throw new NullPointerException();
+        if (usePrimHashMap(key)) {
+            return primHashMapComputeIfAbsent(key, mappingFunction);
+        }
+        int hash = hash(key);
+        Node<K,V>[] tab; Node<K,V> first; int n, i;
+        int binCount = 0;
+        TreeNode<K,V> t = null;
+        Node<K,V> old = null;
+        if (size > threshold || (tab = table) == null ||
+            (n = tab.length) == 0)
+            n = (tab = resize()).length;
+        if ((first = tab[i = (n - 1) & hash]) != null) {
+            if (first instanceof TreeNode)
+                old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key);
+            else {
+                Node<K,V> e = first; K k;
+                do {
+                    if (e.hash == hash &&
+                        ((k = e.key) == key || (key != null && key.equals(k)))) {
+                        old = e;
+                        break;
+                    }
+                    ++binCount;
+                } while ((e = e.next) != null);
+            }
+            V oldValue;
+            if (old != null && (oldValue = old.value) != null) {
+                afterNodeAccess(old);
+                return oldValue;
+            }
+        }
+        int mc = modCount;
+        V v = mappingFunction.apply(key);
+        if (mc != modCount) { throw new ConcurrentModificationException(); }
+        if (v == null) {
+            return null;
+        } else if (old != null) {
+            old.value = v;
+            afterNodeAccess(old);
+            return v;
+        }
+        else if (t != null)
+            t.putTreeVal(this, tab, hash, key, v);
+        else {
+            tab[i] = newNode(hash, key, v, first);
+            if (binCount >= TREEIFY_THRESHOLD - 1)
+                treeifyBin(tab, hash);
+        }
+        modCount = mc + 1;
+        ++size;
+        afterNodeInsertion(true);
+        return v;
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * <p>This method will, on a best-effort basis, throw a
+     * {@link ConcurrentModificationException} if it is detected that the
+     * remapping function modifies this map during computation.
+     *
+     * @throws ConcurrentModificationException if it is detected that the
+     * remapping function modified this map
+     */
+    @Override
+    public V computeIfPresent(K key,
+                              BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+        if (remappingFunction == null)
+            throw new NullPointerException();
+        if (usePrimHashMap(key)) {
+            return primHashMapComputeIfPresent(key, remappingFunction);
+        }
+        Node<K,V> e; V oldValue;
+        if ((e = getNode(key)) != null &&
+            (oldValue = e.value) != null) {
+            int mc = modCount;
+            V v = remappingFunction.apply(key, oldValue);
+            if (mc != modCount) { throw new ConcurrentModificationException(); }
+            if (v != null) {
+                e.value = v;
+                afterNodeAccess(e);
+                return v;
+            }
+            else {
+                int hash = hash(key);
+                removeNode(hash, key, null, false, true);
+            }
+        }
+        return null;
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * <p>This method will, on a best-effort basis, throw a
+     * {@link ConcurrentModificationException} if it is detected that the
+     * remapping function modifies this map during computation.
+     *
+     * @throws ConcurrentModificationException if it is detected that the
+     * remapping function modified this map
+     */
+    @Override
+    public V compute(K key,
+                     BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+        if (remappingFunction == null)
+            throw new NullPointerException();
+        if (usePrimHashMap(key)) {
+            return primHashMapCompute(key, remappingFunction);
+        }
+        int hash = hash(key);
+        Node<K,V>[] tab; Node<K,V> first; int n, i;
+        int binCount = 0;
+        TreeNode<K,V> t = null;
+        Node<K,V> old = null;
+        if (size > threshold || (tab = table) == null ||
+            (n = tab.length) == 0)
+            n = (tab = resize()).length;
+        if ((first = tab[i = (n - 1) & hash]) != null) {
+            if (first instanceof TreeNode)
+                old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key);
+            else {
+                Node<K,V> e = first; K k;
+                do {
+                    if (e.hash == hash &&
+                        ((k = e.key) == key || (key != null && key.equals(k)))) {
+                        old = e;
+                        break;
+                    }
+                    ++binCount;
+                } while ((e = e.next) != null);
+            }
+        }
+        V oldValue = (old == null) ? null : old.value;
+        int mc = modCount;
+        V v = remappingFunction.apply(key, oldValue);
+        if (mc != modCount) { throw new ConcurrentModificationException(); }
+        if (old != null) {
+            if (v != null) {
+                old.value = v;
+                afterNodeAccess(old);
+            }
+            else
+                removeNode(hash, key, null, false, true);
+        }
+        else if (v != null) {
+            if (t != null)
+                t.putTreeVal(this, tab, hash, key, v);
+            else {
+                tab[i] = newNode(hash, key, v, first);
+                if (binCount >= TREEIFY_THRESHOLD - 1)
+                    treeifyBin(tab, hash);
+            }
+            modCount = mc + 1;
+            ++size;
+            afterNodeInsertion(true);
+        }
+        return v;
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * <p>This method will, on a best-effort basis, throw a
+     * {@link ConcurrentModificationException} if it is detected that the
+     * remapping function modifies this map during computation.
+     *
+     * @throws ConcurrentModificationException if it is detected that the
+     * remapping function modified this map
+     */
+    @Override
+    public V merge(K key, V value,
+                   BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
+        if (value == null || remappingFunction == null)
+            throw new NullPointerException();
+        if (usePrimHashMap(key)) {
+            return primHashMapMerge(key, value, remappingFunction);
+        }
+        int hash = hash(key);
+        Node<K,V>[] tab; Node<K,V> first; int n, i;
+        int binCount = 0;
+        TreeNode<K,V> t = null;
+        Node<K,V> old = null;
+        if (size > threshold || (tab = table) == null ||
+            (n = tab.length) == 0)
+            n = (tab = resize()).length;
+        if ((first = tab[i = (n - 1) & hash]) != null) {
+            if (first instanceof TreeNode)
+                old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key);
+            else {
+                Node<K,V> e = first; K k;
+                do {
+                    if (e.hash == hash &&
+                        ((k = e.key) == key || (key != null && key.equals(k)))) {
+                        old = e;
+                        break;
+                    }
+                    ++binCount;
+                } while ((e = e.next) != null);
+            }
+        }
+        if (old != null) {
+            V v;
+            if (old.value != null) {
+                int mc = modCount;
+                v = remappingFunction.apply(old.value, value);
+                if (mc != modCount) {
+                    throw new ConcurrentModificationException();
+                }
+            } else {
+                v = value;
+            }
+            if (v != null) {
+                old.value = v;
+                afterNodeAccess(old);
+            }
+            else
+                removeNode(hash, key, null, false, true);
+            return v;
+        } else {
+            if (t != null)
+                t.putTreeVal(this, tab, hash, key, value);
+            else {
+                tab[i] = newNode(hash, key, value, first);
+                if (binCount >= TREEIFY_THRESHOLD - 1)
+                    treeifyBin(tab, hash);
+            }
+            ++modCount;
+            ++size;
+            afterNodeInsertion(true);
+            return value;
+        }
+    }
+
+    @Override
+    public void forEach(BiConsumer<? super K, ? super V> action) {
+        if (action == null)
+            throw new NullPointerException();
+        int mc = modCount;
+        if (usePrimHashMap()) {
+            int remaining = size;
+            if (primMapNullKeyValid) {
+                action.accept(null, primMapValOfNullKey);
+                --remaining;
+            }
+            if (remaining > 0) {
+                boolean[] valids = primMapValids;
+                Long[] keys = primMapKeys;
+                V[] values = primMapValues;
+                int length = valids.length;
+                for (int i = 0; remaining > 0 && i < length; ++i) {
+                    if (valids[i]) {
+                        action.accept(castKeyToGenericType(keys[i]), values[i]);
+                        --remaining;
+                    }
+                }
+            }
+            if (remaining != 0) {
+                throw new ConcurrentModificationException();
+            }
+        } else {
+            Node<K,V>[] tab;
+            if (size > 0 && (tab = table) != null) {
+                for (Node<K,V> e : tab) {
+                    for (; e != null; e = e.next)
+                        action.accept(e.key, e.value);
+                }
+            }
+        }
+        if (modCount != mc)
+            throw new ConcurrentModificationException();
+    }
+
+    @Override
+    public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
+        if (function == null)
+            throw new NullPointerException();
+        if (usePrimHashMap()) {
+            int mc = modCount;
+            int remaining = size;
+            if (primMapNullKeyValid) {
+                primMapValOfNullKey = function.apply(null, primMapValOfNullKey);
+                --remaining;
+            }
+            if (remaining > 0) {
+                boolean[] valids = primMapValids;
+                Long[] keys = primMapKeys;
+                V[] values = primMapValues;
+                int length = valids.length;
+                for (int i = 0; remaining > 0 && i < length; ++i) {
+                    if (valids[i]) {
+                        values[i] = function.apply(castKeyToGenericType(keys[i]), values[i]);
+                        --remaining;
+                    }
+                }
+            }
+            if (remaining != 0) {
+                throw new ConcurrentModificationException();
+            }
+            if (modCount != mc)
+                throw new ConcurrentModificationException();
+        } else {
+            Node<K,V>[] tab;
+            if (size > 0 && (tab = table) != null) {
+                int mc = modCount;
+                for (Node<K,V> e : tab) {
+                    for (; e != null; e = e.next) {
+                        e.value = function.apply(e.key, e.value);
+                    }
+                }
+                if (modCount != mc)
+                    throw new ConcurrentModificationException();
+            }
+        }
+    }
+
+    /* ------------------------------------------------------------ */
+    // Cloning and serialization
+
+    /**
+     * Returns a shallow copy of this {@code HashMap} instance: the keys and
+     * values themselves are not cloned.
+     *
+     * @return a shallow copy of this map
+     */
+    @SuppressWarnings("unchecked")
+    @Override
+    public Object clone() {
+        HashMap<K,V> result;
+        try {
+            result = (HashMap<K,V>)super.clone();
+        } catch (CloneNotSupportedException e) {
+            // this shouldn't happen, since we are Cloneable
+            throw new InternalError(e);
+        }
+        result.reinitialize();
+        result.putMapEntries(this, false);
+        return result;
+    }
+
+    // These methods are also used when serializing HashSets
+    final float loadFactor() { return loadFactor; }
+    final int capacity() {
+        if (usePrimHashMap()) {
+            return (primMapValids != null) ? primMapValids.length :
+                (threshold > 0) ? threshold :
+                DEFAULT_INITIAL_CAPACITY;
+        }
+        return (table != null) ? table.length :
+            (threshold > 0) ? threshold :
+            DEFAULT_INITIAL_CAPACITY;
+    }
+
+    /**
+     * Saves this map to a stream (that is, serializes it).
+     *
+     * @param s the stream
+     * @throws IOException if an I/O error occurs
+     * @serialData The <i>capacity</i> of the HashMap (the length of the
+     *             bucket array) is emitted (int), followed by the
+     *             <i>size</i> (an int, the number of key-value
+     *             mappings), followed by the key (Object) and value (Object)
+     *             for each key-value mapping.  The key-value mappings are
+     *             emitted in no particular order.
+     */
+    @java.io.Serial
+    private void writeObject(java.io.ObjectOutputStream s)
+        throws IOException {
+        int buckets = capacity();
+        // Write out the threshold, loadfactor, and any hidden stuff
+        s.defaultWriteObject();
+        s.writeInt(buckets);
+        s.writeInt(size);
+        internalWriteEntries(s);
+    }
+
+    /**
+     * Reconstitutes this map from a stream (that is, deserializes it).
+     * @param s the stream
+     * @throws ClassNotFoundException if the class of a serialized object
+     *         could not be found
+     * @throws IOException if an I/O error occurs
+     */
+    @java.io.Serial
+    private void readObject(ObjectInputStream s)
+        throws IOException, ClassNotFoundException {
+
+        ObjectInputStream.GetField fields = s.readFields();
+
+        // Read loadFactor (ignore threshold)
+        float lf = fields.get("loadFactor", 0.75f);
+        if (lf <= 0 || Float.isNaN(lf))
+            throw new InvalidObjectException("Illegal load factor: " + lf);
+
+        lf = Math.min(Math.max(0.25f, lf), 4.0f);
+        HashMap.UnsafeHolder.putLoadFactor(this, lf);
+
+        reinitialize();
+
+        s.readInt();                // Read and ignore number of buckets
+        int mappings = s.readInt(); // Read number of mappings (size)
+        if (mappings < 0) {
+            throw new InvalidObjectException("Illegal mappings count: " + mappings);
+        } else if (mappings == 0) {
+            // use defaults
+        } else if (mappings > 0) {
+            float fc = (float)mappings / lf + 1.0f;
+            int cap = ((fc < DEFAULT_INITIAL_CAPACITY) ?
+                       DEFAULT_INITIAL_CAPACITY :
+                       (fc >= MAXIMUM_CAPACITY) ?
+                       MAXIMUM_CAPACITY :
+                       tableSizeFor((int)fc));
+            // null table will use threshold as initial size.
+            // set threshold to cap here to make sure that table.size is power of 2
+            threshold = cap;
+
+            // Check Map.Entry[].class since it's the nearest public type to
+            // what we're actually creating.
+            SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Map.Entry[].class, cap);
+
+            // Read the keys and values, and put the mappings in the HashMap
+            for (int i = 0; i < mappings; i++) {
+                @SuppressWarnings("unchecked")
+                    K key = (K) s.readObject();
+                @SuppressWarnings("unchecked")
+                    V value = (V) s.readObject();
+                if (usePrimHashMap(key)) {
+                    primHashMapPutVal((Long)key, value,false);
+                } else {
+                    putVal(key, value, false, false, true);
+                }
+            }
+        }
+    }
+
+    // Support for resetting final field during deserializing
+    private static final class UnsafeHolder {
+        private UnsafeHolder() { throw new InternalError(); }
+        private static final jdk.internal.misc.Unsafe unsafe
+                = jdk.internal.misc.Unsafe.getUnsafe();
+        private static final long LF_OFFSET
+                = unsafe.objectFieldOffset(HashMap.class, "loadFactor");
+        static void putLoadFactor(HashMap<?, ?> map, float lf) {
+            unsafe.putFloat(map, LF_OFFSET, lf);
+        }
+    }
+
+    /* ------------------------------------------------------------ */
+    // iterators
+
+    abstract class HashIterator {
+        Node<K,V> next;        // next entry to return
+        Node<K,V> current;     // current entry
+        int expectedModCount;  // for fast-fail
+        int index;             // current slot
+
+        HashIterator() {
+            expectedModCount = modCount;
+            Node<K,V>[] t = table;
+            current = next = null;
+            index = 0;
+            if (t != null && size > 0) { // advance to first entry
+                do {} while (index < t.length && (next = t[index++]) == null);
+            }
+        }
+
+        public final boolean hasNext() {
+            return next != null;
+        }
+
+        final Node<K,V> nextNode() {
+            Node<K,V>[] t;
+            Node<K,V> e = next;
+            if (modCount != expectedModCount)
+                throw new ConcurrentModificationException();
+            if (e == null)
+                throw new NoSuchElementException();
+            if ((next = (current = e).next) == null && (t = table) != null) {
+                do {} while (index < t.length && (next = t[index++]) == null);
+            }
+            return e;
+        }
+
+        public final void remove() {
+            Node<K,V> p = current;
+            if (p == null)
+                throw new IllegalStateException();
+            if (modCount != expectedModCount)
+                throw new ConcurrentModificationException();
+            current = null;
+            removeNode(p.hash, p.key, null, false, false);
+            expectedModCount = modCount;
+        }
+    }
+
+    final class KeyIterator extends HashIterator
+        implements Iterator<K> {
+        public final K next() { return nextNode().key; }
+    }
+
+    final class ValueIterator extends HashIterator
+        implements Iterator<V> {
+        public final V next() { return nextNode().value; }
+    }
+
+    final class EntryIterator extends HashIterator
+        implements Iterator<Map.Entry<K,V>> {
+        public final Map.Entry<K,V> next() { return nextNode(); }
+    }
+
+    /* ------------------------------------------------------------ */
+    // spliterators
+
+    static class HashMapSpliterator<K,V> {
+        final HashMap<K,V> map;
+        Node<K,V> current;          // current node
+        int index;                  // current index, modified on advance/split
+        int fence;                  // one past last index
+        int est;                    // size estimate
+        int expectedModCount;       // for comodification checks
+
+        HashMapSpliterator(HashMap<K,V> m, int origin,
+                           int fence, int est,
+                           int expectedModCount) {
+            // rollback to genericMap if this static class is created directly
+            // e.g. HashSet.spliterator
+            m.rollbackToGenericMap();
+            this.map = m;
+            this.index = origin;
+            this.fence = fence;
+            this.est = est;
+            this.expectedModCount = expectedModCount;
+        }
+
+        final int getFence() { // initialize fence and size on first use
+            int hi;
+            if ((hi = fence) < 0) {
+                HashMap<K,V> m = map;
+                est = m.size;
+                expectedModCount = m.modCount;
+                Node<K,V>[] tab = m.table;
+                hi = fence = (tab == null) ? 0 : tab.length;
+            }
+            return hi;
+        }
+
+        public final long estimateSize() {
+            getFence(); // force init
+            return (long) est;
+        }
+    }
+
+    static final class KeySpliterator<K,V>
+        extends HashMapSpliterator<K,V>
+        implements Spliterator<K> {
+        KeySpliterator(HashMap<K,V> m, int origin, int fence, int est,
+                       int expectedModCount) {
+            super(m, origin, fence, est, expectedModCount);
+        }
+
+        public KeySpliterator<K,V> trySplit() {
+            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
+            return (lo >= mid || current != null) ? null :
+                new KeySpliterator<>(map, lo, index = mid, est >>>= 1,
+                                        expectedModCount);
+        }
+
+        public void forEachRemaining(Consumer<? super K> action) {
+            int i, hi, mc;
+            if (action == null)
+                throw new NullPointerException();
+            HashMap<K,V> m = map;
+            Node<K,V>[] tab = m.table;
+            if ((hi = fence) < 0) {
+                mc = expectedModCount = m.modCount;
+                hi = fence = (tab == null) ? 0 : tab.length;
+            }
+            else
+                mc = expectedModCount;
+            if (tab != null && tab.length >= hi &&
+                (i = index) >= 0 && (i < (index = hi) || current != null)) {
+                Node<K,V> p = current;
+                current = null;
+                do {
+                    if (p == null)
+                        p = tab[i++];
+                    else {
+                        action.accept(p.key);
+                        p = p.next;
+                    }
+                } while (p != null || i < hi);
+                if (m.modCount != mc)
+                    throw new ConcurrentModificationException();
+            }
+        }
+
+        public boolean tryAdvance(Consumer<? super K> action) {
+            int hi;
+            if (action == null)
+                throw new NullPointerException();
+            Node<K,V>[] tab = map.table;
+            if (tab != null && tab.length >= (hi = getFence()) && index >= 0) {
+                while (current != null || index < hi) {
+                    if (current == null)
+                        current = tab[index++];
+                    else {
+                        K k = current.key;
+                        current = current.next;
+                        action.accept(k);
+                        if (map.modCount != expectedModCount)
+                            throw new ConcurrentModificationException();
+                        return true;
+                    }
+                }
+            }
+            return false;
+        }
+
+        public int characteristics() {
+            return (fence < 0 || est == map.size ? Spliterator.SIZED : 0) |
+                Spliterator.DISTINCT;
+        }
+    }
+
+    static final class ValueSpliterator<K,V>
+        extends HashMapSpliterator<K,V>
+        implements Spliterator<V> {
+        ValueSpliterator(HashMap<K,V> m, int origin, int fence, int est,
+                         int expectedModCount) {
+            super(m, origin, fence, est, expectedModCount);
+        }
+
+        public ValueSpliterator<K,V> trySplit() {
+            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
+            return (lo >= mid || current != null) ? null :
+                new ValueSpliterator<>(map, lo, index = mid, est >>>= 1,
+                                          expectedModCount);
+        }
+
+        public void forEachRemaining(Consumer<? super V> action) {
+            int i, hi, mc;
+            if (action == null)
+                throw new NullPointerException();
+            HashMap<K,V> m = map;
+            Node<K,V>[] tab = m.table;
+            if ((hi = fence) < 0) {
+                mc = expectedModCount = m.modCount;
+                hi = fence = (tab == null) ? 0 : tab.length;
+            }
+            else
+                mc = expectedModCount;
+            if (tab != null && tab.length >= hi &&
+                (i = index) >= 0 && (i < (index = hi) || current != null)) {
+                Node<K,V> p = current;
+                current = null;
+                do {
+                    if (p == null)
+                        p = tab[i++];
+                    else {
+                        action.accept(p.value);
+                        p = p.next;
+                    }
+                } while (p != null || i < hi);
+                if (m.modCount != mc)
+                    throw new ConcurrentModificationException();
+            }
+        }
+
+        public boolean tryAdvance(Consumer<? super V> action) {
+            int hi;
+            if (action == null)
+                throw new NullPointerException();
+            Node<K,V>[] tab = map.table;
+            if (tab != null && tab.length >= (hi = getFence()) && index >= 0) {
+                while (current != null || index < hi) {
+                    if (current == null)
+                        current = tab[index++];
+                    else {
+                        V v = current.value;
+                        current = current.next;
+                        action.accept(v);
+                        if (map.modCount != expectedModCount)
+                            throw new ConcurrentModificationException();
+                        return true;
+                    }
+                }
+            }
+            return false;
+        }
+
+        public int characteristics() {
+            return (fence < 0 || est == map.size ? Spliterator.SIZED : 0);
+        }
+    }
+
+    static final class EntrySpliterator<K,V>
+        extends HashMapSpliterator<K,V>
+        implements Spliterator<Map.Entry<K,V>> {
+        EntrySpliterator(HashMap<K,V> m, int origin, int fence, int est,
+                         int expectedModCount) {
+            super(m, origin, fence, est, expectedModCount);
+        }
+
+        public EntrySpliterator<K,V> trySplit() {
+            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
+            return (lo >= mid || current != null) ? null :
+                new EntrySpliterator<>(map, lo, index = mid, est >>>= 1,
+                                          expectedModCount);
+        }
+
+        public void forEachRemaining(Consumer<? super Map.Entry<K,V>> action) {
+            int i, hi, mc;
+            if (action == null)
+                throw new NullPointerException();
+            HashMap<K,V> m = map;
+            Node<K,V>[] tab = m.table;
+            if ((hi = fence) < 0) {
+                mc = expectedModCount = m.modCount;
+                hi = fence = (tab == null) ? 0 : tab.length;
+            }
+            else
+                mc = expectedModCount;
+            if (tab != null && tab.length >= hi &&
+                (i = index) >= 0 && (i < (index = hi) || current != null)) {
+                Node<K,V> p = current;
+                current = null;
+                do {
+                    if (p == null)
+                        p = tab[i++];
+                    else {
+                        action.accept(p);
+                        p = p.next;
+                    }
+                } while (p != null || i < hi);
+                if (m.modCount != mc)
+                    throw new ConcurrentModificationException();
+            }
+        }
+
+        public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) {
+            int hi;
+            if (action == null)
+                throw new NullPointerException();
+            Node<K,V>[] tab = map.table;
+            if (tab != null && tab.length >= (hi = getFence()) && index >= 0) {
+                while (current != null || index < hi) {
+                    if (current == null)
+                        current = tab[index++];
+                    else {
+                        Node<K,V> e = current;
+                        current = current.next;
+                        action.accept(e);
+                        if (map.modCount != expectedModCount)
+                            throw new ConcurrentModificationException();
+                        return true;
+                    }
+                }
+            }
+            return false;
+        }
+
+        public int characteristics() {
+            return (fence < 0 || est == map.size ? Spliterator.SIZED : 0) |
+                Spliterator.DISTINCT;
+        }
+    }
+
+    /* ------------------------------------------------------------ */
+    // LinkedHashMap support
+
+
+    /*
+     * The following package-protected methods are designed to be
+     * overridden by LinkedHashMap, but not by any other subclass.
+     * Nearly all other internal methods are also package-protected
+     * but are declared final, so can be used by LinkedHashMap, view
+     * classes, and HashSet.
+     */
+
+    // Create a regular (non-tree) node
+    Node<K,V> newNode(int hash, K key, V value, Node<K,V> next) {
+        return new Node<>(hash, key, value, next);
+    }
+
+    // For conversion from TreeNodes to plain nodes
+    Node<K,V> replacementNode(Node<K,V> p, Node<K,V> next) {
+        return new Node<>(p.hash, p.key, p.value, next);
+    }
+
+    // Create a tree bin node
+    TreeNode<K,V> newTreeNode(int hash, K key, V value, Node<K,V> next) {
+        return new TreeNode<>(hash, key, value, next);
+    }
+
+    // For treeifyBin
+    TreeNode<K,V> replacementTreeNode(Node<K,V> p, Node<K,V> next) {
+        return new TreeNode<>(p.hash, p.key, p.value, next);
+    }
+
+    /**
+     * Reset to initial default state.  Called by clone and readObject.
+     */
+    void reinitialize() {
+        table = null;
+        entrySet = null;
+        keySet = null;
+        values = null;
+        modCount = 0;
+        threshold = 0;
+        size = 0;
+        primMapValids = null;
+        primMapKeys = null;
+        primMapValues = null;
+        primMapNullKeyValid = false;
+        primMapValOfNullKey = null;
+        // loadFactor should be le than 0.8f to make sure there is at least one empty slot for prim raw array
+        if (loadFactor > MAX_LOAD_FACTOR_FOR_PRIM_MAP) {
+            disablePrimHashMap();
+        } else {
+            initUsingPrimHashMap();
+        }
+    }
+
+    // Callbacks to allow LinkedHashMap post-actions
+    void afterNodeAccess(Node<K,V> p) { }
+    void afterNodeInsertion(boolean evict) { }
+    void afterNodeRemoval(Node<K,V> p) { }
+
+    // Called only from writeObject, to ensure compatible ordering.
+    void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
+        int remaining = size;
+        if (usePrimHashMap()) {
+            if (primMapNullKeyValid) {
+                s.writeObject(null);
+                s.writeObject(primMapValOfNullKey);
+                --remaining;
+            }
+            if (remaining > 0) {
+                boolean[] valids = primMapValids;
+                Long[] keys = primMapKeys;
+                V[] values = primMapValues;
+                int length = valids.length;
+                for (int i = 0; remaining > 0 && i < length; ++i) {
+                    if (valids[i]) {
+                        s.writeObject(castKeyToGenericType(keys[i]));
+                        s.writeObject(values[i]);
+                        --remaining;
+                    }
+                }
+            }
+        } else {
+            Node<K,V>[] tab;
+            if (size > 0 && (tab = table) != null) {
+                for (Node<K,V> e : tab) {
+                    for (; e != null; e = e.next) {
+                        s.writeObject(e.key);
+                        s.writeObject(e.value);
+                        --remaining;
+                    }
+                }
+            }
+        }
+
+        if (remaining != 0) {
+            throw new ConcurrentModificationException();
+        }
+    }
+
+    /* ------------------------------------------------------------ */
+    // Tree bins
+
+    /**
+     * Entry for Tree bins. Extends LinkedHashMap.Entry (which in turn
+     * extends Node) so can be used as extension of either regular or
+     * linked node.
+     */
+    static final class TreeNode<K,V> extends LinkedHashMap.Entry<K,V> {
+        TreeNode<K,V> parent;  // red-black tree links
+        TreeNode<K,V> left;
+        TreeNode<K,V> right;
+        TreeNode<K,V> prev;    // needed to unlink next upon deletion
+        boolean red;
+        TreeNode(int hash, K key, V val, Node<K,V> next) {
+            super(hash, key, val, next);
+        }
+
+        /**
+         * Returns root of tree containing this node.
+         */
+        final TreeNode<K,V> root() {
+            for (TreeNode<K,V> r = this, p;;) {
+                if ((p = r.parent) == null)
+                    return r;
+                r = p;
+            }
+        }
+
+        /**
+         * Ensures that the given root is the first node of its bin.
+         */
+        static <K,V> void moveRootToFront(Node<K,V>[] tab, TreeNode<K,V> root) {
+            int n;
+            if (root != null && tab != null && (n = tab.length) > 0) {
+                int index = (n - 1) & root.hash;
+                TreeNode<K,V> first = (TreeNode<K,V>)tab[index];
+                if (root != first) {
+                    Node<K,V> rn;
+                    tab[index] = root;
+                    TreeNode<K,V> rp = root.prev;
+                    if ((rn = root.next) != null)
+                        ((TreeNode<K,V>)rn).prev = rp;
+                    if (rp != null)
+                        rp.next = rn;
+                    if (first != null)
+                        first.prev = root;
+                    root.next = first;
+                    root.prev = null;
+                }
+                assert checkInvariants(root);
+            }
+        }
+
+        /**
+         * Finds the node starting at root p with the given hash and key.
+         * The kc argument caches comparableClassFor(key) upon first use
+         * comparing keys.
+         */
+        final TreeNode<K,V> find(int h, Object k, Class<?> kc) {
+            TreeNode<K,V> p = this;
+            do {
+                int ph, dir; K pk;
+                TreeNode<K,V> pl = p.left, pr = p.right, q;
+                if ((ph = p.hash) > h)
+                    p = pl;
+                else if (ph < h)
+                    p = pr;
+                else if ((pk = p.key) == k || (k != null && k.equals(pk)))
+                    return p;
+                else if (pl == null)
+                    p = pr;
+                else if (pr == null)
+                    p = pl;
+                else if ((kc != null ||
+                          (kc = comparableClassFor(k)) != null) &&
+                         (dir = compareComparables(kc, k, pk)) != 0)
+                    p = (dir < 0) ? pl : pr;
+                else if ((q = pr.find(h, k, kc)) != null)
+                    return q;
+                else
+                    p = pl;
+            } while (p != null);
+            return null;
+        }
+
+        /**
+         * Calls find for root node.
+         */
+        final TreeNode<K,V> getTreeNode(int h, Object k) {
+            return ((parent != null) ? root() : this).find(h, k, null);
+        }
+
+        /**
+         * Tie-breaking utility for ordering insertions when equal
+         * hashCodes and non-comparable. We don't require a total
+         * order, just a consistent insertion rule to maintain
+         * equivalence across rebalancings. Tie-breaking further than
+         * necessary simplifies testing a bit.
+         */
+        static int tieBreakOrder(Object a, Object b) {
+            int d;
+            if (a == null || b == null ||
+                (d = a.getClass().getName().
+                 compareTo(b.getClass().getName())) == 0)
+                d = (System.identityHashCode(a) <= System.identityHashCode(b) ?
+                     -1 : 1);
+            return d;
+        }
+
+        /**
+         * Forms tree of the nodes linked from this node.
+         */
+        final void treeify(Node<K,V>[] tab) {
+            TreeNode<K,V> root = null;
+            for (TreeNode<K,V> x = this, next; x != null; x = next) {
+                next = (TreeNode<K,V>)x.next;
+                x.left = x.right = null;
+                if (root == null) {
+                    x.parent = null;
+                    x.red = false;
+                    root = x;
+                }
+                else {
+                    K k = x.key;
+                    int h = x.hash;
+                    Class<?> kc = null;
+                    for (TreeNode<K,V> p = root;;) {
+                        int dir, ph;
+                        K pk = p.key;
+                        if ((ph = p.hash) > h)
+                            dir = -1;
+                        else if (ph < h)
+                            dir = 1;
+                        else if ((kc == null &&
+                                  (kc = comparableClassFor(k)) == null) ||
+                                 (dir = compareComparables(kc, k, pk)) == 0)
+                            dir = tieBreakOrder(k, pk);
+
+                        TreeNode<K,V> xp = p;
+                        if ((p = (dir <= 0) ? p.left : p.right) == null) {
+                            x.parent = xp;
+                            if (dir <= 0)
+                                xp.left = x;
+                            else
+                                xp.right = x;
+                            root = balanceInsertion(root, x);
+                            break;
+                        }
+                    }
+                }
+            }
+            moveRootToFront(tab, root);
+        }
+
+        /**
+         * Returns a list of non-TreeNodes replacing those linked from
+         * this node.
+         */
+        final Node<K,V> untreeify(HashMap<K,V> map) {
+            Node<K,V> hd = null, tl = null;
+            for (Node<K,V> q = this; q != null; q = q.next) {
+                Node<K,V> p = map.replacementNode(q, null);
+                if (tl == null)
+                    hd = p;
+                else
+                    tl.next = p;
+                tl = p;
+            }
+            return hd;
+        }
+
+        /**
+         * Tree version of putVal.
+         */
+        final TreeNode<K,V> putTreeVal(HashMap<K,V> map, Node<K,V>[] tab,
+                                       int h, K k, V v) {
+            Class<?> kc = null;
+            boolean searched = false;
+            TreeNode<K,V> root = (parent != null) ? root() : this;
+            for (TreeNode<K,V> p = root;;) {
+                int dir, ph; K pk;
+                if ((ph = p.hash) > h)
+                    dir = -1;
+                else if (ph < h)
+                    dir = 1;
+                else if ((pk = p.key) == k || (k != null && k.equals(pk)))
+                    return p;
+                else if ((kc == null &&
+                          (kc = comparableClassFor(k)) == null) ||
+                         (dir = compareComparables(kc, k, pk)) == 0) {
+                    if (!searched) {
+                        TreeNode<K,V> q, ch;
+                        searched = true;
+                        if (((ch = p.left) != null &&
+                             (q = ch.find(h, k, kc)) != null) ||
+                            ((ch = p.right) != null &&
+                             (q = ch.find(h, k, kc)) != null))
+                            return q;
+                    }
+                    dir = tieBreakOrder(k, pk);
+                }
+
+                TreeNode<K,V> xp = p;
+                if ((p = (dir <= 0) ? p.left : p.right) == null) {
+                    Node<K,V> xpn = xp.next;
+                    TreeNode<K,V> x = map.newTreeNode(h, k, v, xpn);
+                    if (dir <= 0)
+                        xp.left = x;
+                    else
+                        xp.right = x;
+                    xp.next = x;
+                    x.parent = x.prev = xp;
+                    if (xpn != null)
+                        ((TreeNode<K,V>)xpn).prev = x;
+                    moveRootToFront(tab, balanceInsertion(root, x));
+                    return null;
+                }
+            }
+        }
+
+        /**
+         * Removes the given node, that must be present before this call.
+         * This is messier than typical red-black deletion code because we
+         * cannot swap the contents of an interior node with a leaf
+         * successor that is pinned by "next" pointers that are accessible
+         * independently during traversal. So instead we swap the tree
+         * linkages. If the current tree appears to have too few nodes,
+         * the bin is converted back to a plain bin. (The test triggers
+         * somewhere between 2 and 6 nodes, depending on tree structure).
+         */
+        final void removeTreeNode(HashMap<K,V> map, Node<K,V>[] tab,
+                                  boolean movable) {
+            int n;
+            if (tab == null || (n = tab.length) == 0)
+                return;
+            int index = (n - 1) & hash;
+            TreeNode<K,V> first = (TreeNode<K,V>)tab[index], root = first, rl;
+            TreeNode<K,V> succ = (TreeNode<K,V>)next, pred = prev;
+            if (pred == null)
+                tab[index] = first = succ;
+            else
+                pred.next = succ;
+            if (succ != null)
+                succ.prev = pred;
+            if (first == null)
+                return;
+            if (root.parent != null)
+                root = root.root();
+            if (root == null
+                || (movable
+                    && (root.right == null
+                        || (rl = root.left) == null
+                        || rl.left == null))) {
+                tab[index] = first.untreeify(map);  // too small
+                return;
+            }
+            TreeNode<K,V> p = this, pl = left, pr = right, replacement;
+            if (pl != null && pr != null) {
+                TreeNode<K,V> s = pr, sl;
+                while ((sl = s.left) != null) // find successor
+                    s = sl;
+                boolean c = s.red; s.red = p.red; p.red = c; // swap colors
+                TreeNode<K,V> sr = s.right;
+                TreeNode<K,V> pp = p.parent;
+                if (s == pr) { // p was s's direct parent
+                    p.parent = s;
+                    s.right = p;
+                }
+                else {
+                    TreeNode<K,V> sp = s.parent;
+                    if ((p.parent = sp) != null) {
+                        if (s == sp.left)
+                            sp.left = p;
+                        else
+                            sp.right = p;
+                    }
+                    if ((s.right = pr) != null)
+                        pr.parent = s;
+                }
+                p.left = null;
+                if ((p.right = sr) != null)
+                    sr.parent = p;
+                if ((s.left = pl) != null)
+                    pl.parent = s;
+                if ((s.parent = pp) == null)
+                    root = s;
+                else if (p == pp.left)
+                    pp.left = s;
+                else
+                    pp.right = s;
+                if (sr != null)
+                    replacement = sr;
+                else
+                    replacement = p;
+            }
+            else if (pl != null)
+                replacement = pl;
+            else if (pr != null)
+                replacement = pr;
+            else
+                replacement = p;
+            if (replacement != p) {
+                TreeNode<K,V> pp = replacement.parent = p.parent;
+                if (pp == null)
+                    (root = replacement).red = false;
+                else if (p == pp.left)
+                    pp.left = replacement;
+                else
+                    pp.right = replacement;
+                p.left = p.right = p.parent = null;
+            }
+
+            TreeNode<K,V> r = p.red ? root : balanceDeletion(root, replacement);
+
+            if (replacement == p) {  // detach
+                TreeNode<K,V> pp = p.parent;
+                p.parent = null;
+                if (pp != null) {
+                    if (p == pp.left)
+                        pp.left = null;
+                    else if (p == pp.right)
+                        pp.right = null;
+                }
+            }
+            if (movable)
+                moveRootToFront(tab, r);
+        }
+
+        /**
+         * Splits nodes in a tree bin into lower and upper tree bins,
+         * or untreeifies if now too small. Called only from resize;
+         * see above discussion about split bits and indices.
+         *
+         * @param map the map
+         * @param tab the table for recording bin heads
+         * @param index the index of the table being split
+         * @param bit the bit of hash to split on
+         */
+        final void split(HashMap<K,V> map, Node<K,V>[] tab, int index, int bit) {
+            TreeNode<K,V> b = this;
+            // Relink into lo and hi lists, preserving order
+            TreeNode<K,V> loHead = null, loTail = null;
+            TreeNode<K,V> hiHead = null, hiTail = null;
+            int lc = 0, hc = 0;
+            for (TreeNode<K,V> e = b, next; e != null; e = next) {
+                next = (TreeNode<K,V>)e.next;
+                e.next = null;
+                if ((e.hash & bit) == 0) {
+                    if ((e.prev = loTail) == null)
+                        loHead = e;
+                    else
+                        loTail.next = e;
+                    loTail = e;
+                    ++lc;
+                }
+                else {
+                    if ((e.prev = hiTail) == null)
+                        hiHead = e;
+                    else
+                        hiTail.next = e;
+                    hiTail = e;
+                    ++hc;
+                }
+            }
+
+            if (loHead != null) {
+                if (lc <= UNTREEIFY_THRESHOLD)
+                    tab[index] = loHead.untreeify(map);
+                else {
+                    tab[index] = loHead;
+                    if (hiHead != null) // (else is already treeified)
+                        loHead.treeify(tab);
+                }
+            }
+            if (hiHead != null) {
+                if (hc <= UNTREEIFY_THRESHOLD)
+                    tab[index + bit] = hiHead.untreeify(map);
+                else {
+                    tab[index + bit] = hiHead;
+                    if (loHead != null)
+                        hiHead.treeify(tab);
+                }
+            }
+        }
+
+        /* ------------------------------------------------------------ */
+        // Red-black tree methods, all adapted from CLR
+
+        static <K,V> TreeNode<K,V> rotateLeft(TreeNode<K,V> root,
+                                              TreeNode<K,V> p) {
+            TreeNode<K,V> r, pp, rl;
+            if (p != null && (r = p.right) != null) {
+                if ((rl = p.right = r.left) != null)
+                    rl.parent = p;
+                if ((pp = r.parent = p.parent) == null)
+                    (root = r).red = false;
+                else if (pp.left == p)
+                    pp.left = r;
+                else
+                    pp.right = r;
+                r.left = p;
+                p.parent = r;
+            }
+            return root;
+        }
+
+        static <K,V> TreeNode<K,V> rotateRight(TreeNode<K,V> root,
+                                               TreeNode<K,V> p) {
+            TreeNode<K,V> l, pp, lr;
+            if (p != null && (l = p.left) != null) {
+                if ((lr = p.left = l.right) != null)
+                    lr.parent = p;
+                if ((pp = l.parent = p.parent) == null)
+                    (root = l).red = false;
+                else if (pp.right == p)
+                    pp.right = l;
+                else
+                    pp.left = l;
+                l.right = p;
+                p.parent = l;
+            }
+            return root;
+        }
+
+        static <K,V> TreeNode<K,V> balanceInsertion(TreeNode<K,V> root,
+                                                    TreeNode<K,V> x) {
+            x.red = true;
+            for (TreeNode<K,V> xp, xpp, xppl, xppr;;) {
+                if ((xp = x.parent) == null) {
+                    x.red = false;
+                    return x;
+                }
+                else if (!xp.red || (xpp = xp.parent) == null)
+                    return root;
+                if (xp == (xppl = xpp.left)) {
+                    if ((xppr = xpp.right) != null && xppr.red) {
+                        xppr.red = false;
+                        xp.red = false;
+                        xpp.red = true;
+                        x = xpp;
+                    }
+                    else {
+                        if (x == xp.right) {
+                            root = rotateLeft(root, x = xp);
+                            xpp = (xp = x.parent) == null ? null : xp.parent;
+                        }
+                        if (xp != null) {
+                            xp.red = false;
+                            if (xpp != null) {
+                                xpp.red = true;
+                                root = rotateRight(root, xpp);
+                            }
+                        }
+                    }
+                }
+                else {
+                    if (xppl != null && xppl.red) {
+                        xppl.red = false;
+                        xp.red = false;
+                        xpp.red = true;
+                        x = xpp;
+                    }
+                    else {
+                        if (x == xp.left) {
+                            root = rotateRight(root, x = xp);
+                            xpp = (xp = x.parent) == null ? null : xp.parent;
+                        }
+                        if (xp != null) {
+                            xp.red = false;
+                            if (xpp != null) {
+                                xpp.red = true;
+                                root = rotateLeft(root, xpp);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        static <K,V> TreeNode<K,V> balanceDeletion(TreeNode<K,V> root,
+                                                   TreeNode<K,V> x) {
+            for (TreeNode<K,V> xp, xpl, xpr;;) {
+                if (x == null || x == root)
+                    return root;
+                else if ((xp = x.parent) == null) {
+                    x.red = false;
+                    return x;
+                }
+                else if (x.red) {
+                    x.red = false;
+                    return root;
+                }
+                else if ((xpl = xp.left) == x) {
+                    if ((xpr = xp.right) != null && xpr.red) {
+                        xpr.red = false;
+                        xp.red = true;
+                        root = rotateLeft(root, xp);
+                        xpr = (xp = x.parent) == null ? null : xp.right;
+                    }
+                    if (xpr == null)
+                        x = xp;
+                    else {
+                        TreeNode<K,V> sl = xpr.left, sr = xpr.right;
+                        if ((sr == null || !sr.red) &&
+                            (sl == null || !sl.red)) {
+                            xpr.red = true;
+                            x = xp;
+                        }
+                        else {
+                            if (sr == null || !sr.red) {
+                                if (sl != null)
+                                    sl.red = false;
+                                xpr.red = true;
+                                root = rotateRight(root, xpr);
+                                xpr = (xp = x.parent) == null ?
+                                    null : xp.right;
+                            }
+                            if (xpr != null) {
+                                xpr.red = (xp == null) ? false : xp.red;
+                                if ((sr = xpr.right) != null)
+                                    sr.red = false;
+                            }
+                            if (xp != null) {
+                                xp.red = false;
+                                root = rotateLeft(root, xp);
+                            }
+                            x = root;
+                        }
+                    }
+                }
+                else { // symmetric
+                    if (xpl != null && xpl.red) {
+                        xpl.red = false;
+                        xp.red = true;
+                        root = rotateRight(root, xp);
+                        xpl = (xp = x.parent) == null ? null : xp.left;
+                    }
+                    if (xpl == null)
+                        x = xp;
+                    else {
+                        TreeNode<K,V> sl = xpl.left, sr = xpl.right;
+                        if ((sl == null || !sl.red) &&
+                            (sr == null || !sr.red)) {
+                            xpl.red = true;
+                            x = xp;
+                        }
+                        else {
+                            if (sl == null || !sl.red) {
+                                if (sr != null)
+                                    sr.red = false;
+                                xpl.red = true;
+                                root = rotateLeft(root, xpl);
+                                xpl = (xp = x.parent) == null ?
+                                    null : xp.left;
+                            }
+                            if (xpl != null) {
+                                xpl.red = (xp == null) ? false : xp.red;
+                                if ((sl = xpl.left) != null)
+                                    sl.red = false;
+                            }
+                            if (xp != null) {
+                                xp.red = false;
+                                root = rotateRight(root, xp);
+                            }
+                            x = root;
+                        }
+                    }
+                }
+            }
+        }
+
+        /**
+         * Recursive invariant check
+         */
+        static <K,V> boolean checkInvariants(TreeNode<K,V> t) {
+            TreeNode<K,V> tp = t.parent, tl = t.left, tr = t.right,
+                tb = t.prev, tn = (TreeNode<K,V>)t.next;
+            if (tb != null && tb.next != t)
+                return false;
+            if (tn != null && tn.prev != t)
+                return false;
+            if (tp != null && t != tp.left && t != tp.right)
+                return false;
+            if (tl != null && (tl.parent != t || tl.hash > t.hash))
+                return false;
+            if (tr != null && (tr.parent != t || tr.hash < t.hash))
+                return false;
+            if (t.red && tl != null && tl.red && tr != null && tr.red)
+                return false;
+            if (tl != null && !checkInvariants(tl))
+                return false;
+            if (tr != null && !checkInvariants(tr))
+                return false;
+            return true;
+        }
+    }
+
+    /* ------------------------------------------------------------ */
+    // Primitive long HashMap support
+
+    @SuppressWarnings("unchecked")
+    private K castKeyToGenericType(Long key) {
+        return (K)(key);
+    }
+
+    private void initUsingPrimHashMap() {
+        usingPrimHashMap = true;
+        primMapNullKeyValid = false;
+        primMapValOfNullKey = null;
+    }
+
+    /**
+     * set usingPrimHashMap to false to disable primitive long hashmap
+     */
+    final protected void disablePrimHashMap() {
+        usingPrimHashMap = false;
+    }
+
+    private boolean usePrimHashMap() {
+        return usingPrimHashMap;
+    }
+
+    private boolean usePrimHashMap(Object key) {
+        if (!usingPrimHashMap) {
+            return false;
+        }
+        if (key != null && !(key instanceof Long)) {
+            rollbackToGenericMap();
+            return false;
+        }
+        return true;
+    }
+
+    /**
+     * This method copy prim hash map's key-values to Node<K,V>[] table
+     * and then set usingPrimHashMap to false
+     */
+    private void rollbackToGenericMap() {
+        if (!usePrimHashMap()) {
+            return ;
+        }
+        // add lock to prevent multiple threads from executing the following rollback code:
+        synchronized (this) {
+            if (!usePrimHashMap()) {
+                return ;
+            }
+            if (size > 0) {
+                // null table will use threshold as initial length.
+                // set threshold according size here to make sure that table.size is power of 2
+                threshold = tableSizeFor(size);
+                // take a snapshot to detect concurrent modification
+                int expectedSize = size;
+                int expectedCount = modCount;
+                int remaining = size;
+                // put existing key-value to GenericMap
+                if (primMapNullKeyValid) {
+                    putVal(null, primMapValOfNullKey, false, true, false);
+                    --remaining;
+                }
+                final boolean[] valids = primMapValids;
+                if (valids != null) {
+                    final Long[] keys = primMapKeys;
+                    final V[] values = primMapValues;
+                    int Cap = valids.length;
+                    for (int i = 0; remaining > 0 && i < Cap; ++i) {
+                        if (valids[i]) {
+                            putVal(castKeyToGenericType(keys[i]), values[i], false, true, false);
+                            --remaining;
+                        }
+                    }
+                }
+
+                if (remaining != 0 || expectedSize != size || expectedCount != modCount) {
+                    throw new ConcurrentModificationException();
+                }
+                // Don't set arrays to null. Keep long map's data to avoid concurrent visit NPE
+            }
+            disablePrimHashMap();
+        }
+    }
+
+    /**
+     * Computes hash to get index.
+     */
+    static private int primHashMapCalculateIndex(Object key, final int mask) {
+        return hash(key) & mask;
+    }
+
+    private void primHashMapResize() {
+        final boolean[] oldValids = primMapValids;
+        int oldCap = (oldValids == null) ? 0 : oldValids.length;
+        int newCap = calNewCapAndUpdateThreshold(oldCap);
+        // 0 means oldCap reaches the MAXIMUM_CAPACITY
+        if (newCap == 0) {
+            throw new IllegalStateException("can't resize due to primitive long map reaches the max capacity");
+        }
+
+        final boolean[] newValids = new boolean[newCap];
+        final Long[] newKeys = new Long[newCap];
+        @SuppressWarnings({"rawtypes","unchecked"})
+        final V[] newValues = (V[])new Object[newCap];
+
+        final int mask = newCap - 1;
+        if (oldValids != null) {
+            final Long[] oldKeys = primMapKeys;
+            final V[] oldValues = primMapValues;
+            int remaining = primMapNullKeyValid ? size - 1 : size;
+            for (int i = 0; remaining > 0 && i < oldCap; ++i) {
+                if (oldValids[i]) {
+                    long key = oldKeys[i];
+                    V value = oldValues[i];
+                    int index = primHashMapCalculateIndex(key, mask);
+                    while (newValids[index]) {
+                        index = (++index) & mask;
+                    }
+                    newValids[index] = true;
+                    newKeys[index] = key;
+                    newValues[index] = value;
+                    --remaining;
+                }
+            }
+        }
+        primMapValids = newValids;
+        primMapKeys = newKeys;
+        primMapValues = newValues;
+    }
+
+    /**
+     * Implements Map.put and related methods.
+     *
+     * @param key the key
+     * @param value the value to put
+     * @param onlyIfAbsent if true, don't change existing value
+     * @return previous value, or null if none
+     */
+    private V primHashMapPutVal(Long key, V value, boolean onlyIfAbsent) {
+        if (key == null) {
+            if (primMapNullKeyValid) { // existing mapping for key
+                V oldValue = primMapValOfNullKey;
+                if (!onlyIfAbsent || oldValue == null)
+                    primMapValOfNullKey = value;
+                return oldValue;
+            }
+            primMapNullKeyValid = true;
+            primMapValOfNullKey = value;
+            ++modCount;
+            ++size;
+            return null;
+        }
+        if (primMapValids == null || primMapValids.length == 0) {
+            primHashMapResize();
+        }
+
+        final boolean[] valids = primMapValids;
+        final Long[] keys = primMapKeys;
+        final V[] values = primMapValues;
+        int remainingLength = valids.length;
+        final int mask = remainingLength - 1;
+        int index = primHashMapCalculateIndex(key, mask);
+        // find empty slots to insert
+        while (valids[index] && remainingLength > 0) {
+            if (Objects.equals(keys[index], key)) {
+                break;
+            }
+            index = (++index) & mask;
+            --remainingLength;
+        }
+        if (valids[index]) { // existing mapping for key
+            V oldValue = values[index];
+            if (!onlyIfAbsent || oldValue == null) {
+                values[index] = value;
+            }
+            return oldValue;
+        }
+        keys[index] = key;
+        values[index] = value;
+        valids[index] = true;
+        ++modCount;
+        if (++size > threshold)
+            primHashMapResize();
+        return null;
+    }
+
+    /**
+     * find the key's index in prim hashmap
+     *
+     * @param key the key
+     * @return NULL_KEY_INDEX_FOR_RPIM_MAP if key is null and null key valid,
+     *         related key-index if found,
+     *         or KEY_NO_EXIST_FOR_PRIM_MAP if not found
+     */
+    private int primHashGetIndexByKey(Object key) {
+        if (key == null) {
+            return primMapNullKeyValid ? NULL_KEY_INDEX_FOR_RPIM_MAP : KEY_NO_EXIST_FOR_PRIM_MAP;
+        }
+        if (!(key instanceof Long)) {
+            return KEY_NO_EXIST_FOR_PRIM_MAP;
+        }
+        final boolean[] valids = primMapValids;
+        if (valids == null || valids.length == 0) {
+            return KEY_NO_EXIST_FOR_PRIM_MAP;
+        }
+
+        final Long[] keys = primMapKeys;
+        int remainingLength = valids.length;
+        final int mask = remainingLength - 1;
+        int index = primHashMapCalculateIndex(key, mask);
+        while (valids[index] && remainingLength > 0) {
+            if (Objects.equals(keys[index], key)) {
+                return index;
+            }
+            index = (++index) & mask;
+            --remainingLength;
+        }
+        return KEY_NO_EXIST_FOR_PRIM_MAP;
+    }
+
+    private V primHashMapGetValByIndex(int index) {
+        if (index == KEY_NO_EXIST_FOR_PRIM_MAP) {
+            return null;
+        }
+        return (index == NULL_KEY_INDEX_FOR_RPIM_MAP) ? primMapValOfNullKey : primMapValues[index];
+    }
+
+    private V primHashMapGet(Object key) {
+        int index = primHashGetIndexByKey(key);
+        return primHashMapGetValByIndex(index);
+    }
+
+    private boolean primHashMapContainsValue(Object value) {
+        int remaining = size;
+        if (primMapNullKeyValid) {
+            if (Objects.equals(value, primMapValOfNullKey)) {
+                return true;
+            }
+            --remaining;
+        }
+        final boolean[] valids = primMapValids;
+        if (valids == null || valids.length == 0) {
+            return false;
+        }
+        final V[] values = primMapValues;
+        final int length = valids.length;
+        for (int i = 0; remaining > 0 && i < length; ++i) {
+            if (valids[i]) {
+                if (Objects.equals(value, values[i])) {
+                    return true;
+                }
+                --remaining;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * remove an element from prim hashmap by index.
+     *
+     * @param index the index of element to be removed
+     * @return the value of key, or null if none
+     */
+    private V primHashMapRemoveByIndex(int index) {
+        int removeIdx = index;
+        if (removeIdx == KEY_NO_EXIST_FOR_PRIM_MAP) {
+            return null;
+        }
+        V oldValue;
+        if (removeIdx == NULL_KEY_INDEX_FOR_RPIM_MAP) {
+            oldValue = primMapValOfNullKey;
+            primMapNullKeyValid = false;
+            primMapValOfNullKey = null;
+        } else {
+            oldValue = primMapValues[removeIdx];
+            final boolean[] valids = primMapValids;
+            final V[] values = primMapValues;
+            final Long[] keys = primMapKeys;
+            int mask = valids.length - 1;
+            // Moves the slot, whose expected idx and its actual index overwrite the removed slot, to the removed slot.
+            // Do it recursively until reaching an empty slot(there is always an empty slot since load factor <= 0.8f)
+            int actualIdx = (removeIdx + 1) & mask;
+            while (valids[actualIdx]) {
+                int expectedIdx = primHashMapCalculateIndex(keys[actualIdx], mask);
+                // move actual to remove, then set actual as new remove
+                // |    expectedIdx--->removeIdx--->actualIdx    | or
+                // |--->actualIdx    expectedIdx--->removeIdx--->| or
+                // |--->removeIdx--->actualIdx    expectedIdx--->|
+                if ((expectedIdx <= removeIdx && removeIdx < actualIdx) ||
+                    (expectedIdx > actualIdx && (expectedIdx <= removeIdx || removeIdx < actualIdx))) {
+                    keys[removeIdx] = keys[actualIdx];
+                    values[removeIdx] = values[actualIdx];
+                    removeIdx = actualIdx;
+                }
+                actualIdx = (++actualIdx) & mask;
+            }
+            valids[removeIdx] = false;
+            values[removeIdx] = null;
+        }
+        ++modCount;
+        --size;
+        return oldValue;
+    }
+
+    /**
+     * remove an element from prim hashmap by key.
+     *
+     * @param key the key
+     * @return the value of key, or null if none
+     */
+    private V primHashMapRemoveByKey(Object key) {
+        int index = primHashGetIndexByKey(key);
+        return primHashMapRemoveByIndex(index);
+    }
+
+    private V primHashMapComputeIfAbsent(K key,
+                                         Function<? super K, ? extends V> mappingFunction) {
+        int index = primHashGetIndexByKey(key);
+        V oldValue = primHashMapGetValByIndex(index);
+        if (oldValue != null) {
+            return oldValue;
+        }
+        int mc = modCount;
+        V v = mappingFunction.apply(key);
+        if (mc != modCount) { throw new ConcurrentModificationException(); }
+        if (v == null) {
+            return null;
+        } else if (index != KEY_NO_EXIST_FOR_PRIM_MAP) { // key exist and oldValue is null
+            if (index == NULL_KEY_INDEX_FOR_RPIM_MAP) {
+                primMapValOfNullKey = v;
+            } else {
+                primMapValues[index] = v;
+            }
+            return v;
+        } else { // key not exist
+            primHashMapPutVal((Long)key, v, false);
+            return v;
+        }
+    }
+
+    private V primHashMapComputeIfPresent(K key,
+                                          BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+        int index = primHashGetIndexByKey(key);
+        V oldValue = primHashMapGetValByIndex(index);
+        if (oldValue == null) {
+            return null;
+        }
+
+        int mc = modCount;
+        V v = remappingFunction.apply(key, oldValue);
+        if (mc != modCount) { throw new ConcurrentModificationException(); }
+        if (v == null) {
+            primHashMapRemoveByIndex(index);
+            return null;
+        }
+        if (index == NULL_KEY_INDEX_FOR_RPIM_MAP) {
+            primMapValOfNullKey = v;
+        } else {
+            primMapValues[index] = v;
+        }
+        return v;
+    }
+
+    private V primHashMapCompute(K key,
+                                 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+        int index = primHashGetIndexByKey(key);
+        V oldValue = primHashMapGetValByIndex(index);
+        int mc = modCount;
+        V v = remappingFunction.apply(key, oldValue);
+        if (mc != modCount) { throw new ConcurrentModificationException(); }
+        if (index != KEY_NO_EXIST_FOR_PRIM_MAP) {
+            if (v != null) {
+                if (index == NULL_KEY_INDEX_FOR_RPIM_MAP) {
+                    primMapValOfNullKey = v;
+                } else {
+                    primMapValues[index] = v;
+                }
+            } else {
+                primHashMapRemoveByIndex(index);
+            }
+        } else if (v != null) {
+            primHashMapPutVal((Long)key, v, false);
+        }
+        return v;
+    }
+
+    private V primHashMapMerge(K key, V value,
+                               BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
+        int index = primHashGetIndexByKey(key);
+        V oldValue = primHashMapGetValByIndex(index);
+        if (index != KEY_NO_EXIST_FOR_PRIM_MAP) {
+            V v;
+            if (oldValue != null) {
+                int mc = modCount;
+                v = remappingFunction.apply(oldValue, value);
+                if (mc != modCount) {
+                    throw new ConcurrentModificationException();
+                }
+            } else {
+                v = value;
+            }
+            if (v != null) {
+                if (index == NULL_KEY_INDEX_FOR_RPIM_MAP) {
+                    primMapValOfNullKey = v;
+                } else {
+                    primMapValues[index] = v;
+                }
+            } else {
+                primHashMapRemoveByIndex(index);
+            }
+            return v;
+        } else {
+            primHashMapPutVal((Long)key, value, false);
+            return value;
+        }
+    }
+
+    /**
+     * prim hashmap node, used for key-value iterator.
+     */
+    class primHashMapNode implements Map.Entry<K,V> {
+        final K key;
+        V value;
+        final int nodeIdx;
+
+        primHashMapNode(int nodeIdx) {
+            if (nodeIdx == NULL_KEY_INDEX_FOR_RPIM_MAP) {
+                this.key = null;
+                this.value = HashMap.this.primMapValOfNullKey;
+            } else {
+                this.key = HashMap.this.castKeyToGenericType(HashMap.this.primMapKeys[nodeIdx]);
+                this.value = HashMap.this.primMapValues[nodeIdx];
+            }
+            this.nodeIdx = nodeIdx;
+        }
+
+        public final K getKey()        { return key; }
+        public final V getValue()      { return value; }
+        public final String toString() { return key + "=" + value; }
+
+        public final boolean equals(Object o) {
+            if (o == this)
+                return true;
+
+            return o instanceof Map.Entry<?, ?> e
+                    && Objects.equals(key, e.getKey())
+                    && Objects.equals(value, e.getValue());
+        }
+
+        public final int hashCode() {
+            return Objects.hashCode(key) ^ Objects.hashCode(value);
+        }
+
+        public final V setValue(V newValue) {
+            V oldValue = value;
+            value = newValue;
+            if (nodeIdx == NULL_KEY_INDEX_FOR_RPIM_MAP) {
+                HashMap.this.primMapValOfNullKey = newValue;
+            } else {
+                HashMap.this.primMapValues[nodeIdx] = newValue;
+            }
+            return oldValue;
+        }
+    }
+
+    /* ------------------------------------------------------------ */
+    // prim hashmap iterators
+
+    abstract class primHashMapIterator {
+        int nextIndex;
+        int curIndex;             // current slot
+        int expectedModCount;  // for fast-fail
+        int remaining;
+        int startIndex;
+        int stopIndex;
+        int mask;
+
+        primHashMapIterator() {
+            expectedModCount = modCount;
+            remaining = size;
+            curIndex = nextIndex = KEY_NO_EXIST_FOR_PRIM_MAP;
+            // init startIndex/stopIndex if there are elements in primMapValues
+            if (remaining > (primMapNullKeyValid ? 1 : 0)) {
+                final boolean[] valids = primMapValids;
+                mask = valids.length - 1;
+                // Use reverse traversal to prevent a node from being traversed after it is deleted.
+                // Set stopIndex to the index of the first empty slot (starting from 0), and then set
+                // startIndex to the index of the first valid slot starting from the reverse of stopIndex.
+                stopIndex = 0;
+                while (valids[stopIndex]) {
+                    stopIndex = (++stopIndex) & mask;
+                }
+                startIndex = stopIndex;
+                while (!valids[startIndex]) {
+                    startIndex = (--startIndex) & mask;
+                }
+            } else {
+                startIndex = stopIndex = KEY_NO_EXIST_FOR_PRIM_MAP;
+            }
+
+            if (remaining > 0) { // advance to first entry
+                if (primMapNullKeyValid) { // always set first node to null key if exist
+                    nextIndex = NULL_KEY_INDEX_FOR_RPIM_MAP;
+                } else {
+                    nextIndex = startIndex;
+                }
+            }
+        }
+
+        public final boolean hasNext() {
+            return remaining > 0;
+        }
+
+        final void findNext() {
+            if (modCount != expectedModCount)
+                throw new ConcurrentModificationException();
+            if (nextIndex == KEY_NO_EXIST_FOR_PRIM_MAP) {
+                throw new NoSuchElementException();
+            }
+            curIndex = nextIndex;
+            --remaining;
+            if (remaining > 0) {
+                // startIndex has been calculated if curIndex is null key index
+                if (curIndex != NULL_KEY_INDEX_FOR_RPIM_MAP) {
+                    final boolean[] valids = primMapValids;
+                    while (startIndex != stopIndex) {
+                        startIndex = (--startIndex) & mask;
+                        if (valids[startIndex]) {
+                            break;
+                        }
+                    }
+                }
+                nextIndex = startIndex;
+            } else {
+                nextIndex = KEY_NO_EXIST_FOR_PRIM_MAP;
+            }
+        }
+
+        public final void remove() {
+            if (curIndex == KEY_NO_EXIST_FOR_PRIM_MAP) {
+                throw new IllegalStateException();
+            }
+            if (modCount != expectedModCount)
+                throw new ConcurrentModificationException();
+            primHashMapRemoveByIndex(curIndex);
+            curIndex = KEY_NO_EXIST_FOR_PRIM_MAP;
+            expectedModCount = modCount;
+        }
+    }
+
+    final class primHashMapKeyIterator extends primHashMapIterator
+        implements Iterator<K> {
+        public final K next() {
+            findNext();
+            return (curIndex == NULL_KEY_INDEX_FOR_RPIM_MAP) ? null : castKeyToGenericType(primMapKeys[curIndex]);
+        }
+    }
+
+    final class primHashMapValueIterator extends primHashMapIterator
+        implements Iterator<V> {
+        public final V next() {
+            findNext();
+            return (curIndex == NULL_KEY_INDEX_FOR_RPIM_MAP) ? primMapValOfNullKey : primMapValues[curIndex];
+        }
+    }
+
+    final class primHashMapEntryIterator extends primHashMapIterator
+        implements Iterator<Map.Entry<K,V>> {
+        public final Map.Entry<K,V> next() {
+            findNext();
+            return new primHashMapNode(curIndex);
+        }
+    }
+
+    /* ------------------------------------------------------------ */
+    // prim hashmap spliterators
+
+    abstract class primHashMapSpliterator<T> implements Spliterator<T> {
+        int index;                  // current index, modified on advance/split
+        int fence;                  // one past last index
+        int est;                    // size estimate
+        int expectedModCount;       // for comodification checks
+
+        // indicate whether this spliterator need to process null key or not
+        // always set to false if this spliterator came form trySplit()
+        boolean needToProcessNullKey;
+
+        primHashMapSpliterator(int origin, int fence, int est,
+                               int expectedModCount, boolean needToProcessNullKey) {
+            this.index = origin;
+            this.fence = fence;
+            this.est = est;
+            this.expectedModCount = expectedModCount;
+            this.needToProcessNullKey = needToProcessNullKey;
+        }
+
+        final int getFence() { // initialize fence and size on first use
+            int hi;
+            if ((hi = fence) < 0) {
+                est = size;
+                expectedModCount = modCount;
+                boolean[] valids = primMapValids;
+                hi = fence = (valids == null) ? 0 : valids.length;
+            }
+            return hi;
+        }
+
+        public final long estimateSize() {
+            getFence(); // force init
+            return (long) est;
+        }
+    }
+
+    final class primHashMapKeySpliterator
+        extends primHashMapSpliterator<K> {
+        primHashMapKeySpliterator(int origin, int fence, int est,
+                                  int expectedModCount, boolean needToProcessNullKey) {
+            super(origin, fence, est, expectedModCount, needToProcessNullKey);
+        }
+
+        public primHashMapKeySpliterator trySplit() {
+            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
+            return (lo >= mid) ? null :
+                    new primHashMapKeySpliterator(lo, index = mid, est >>>= 1,
+                                                  expectedModCount, false);
+        }
+
+        public void forEachRemaining(Consumer<? super K> action) {
+            int i, hi, mc;
+            if (action == null)
+                throw new NullPointerException();
+            boolean[] valids = primMapValids;
+            Long[] keys = primMapKeys;
+            if ((hi = fence) < 0) {
+                mc = expectedModCount = modCount;
+                hi = fence = (valids == null) ? 0 : valids.length;
+            }
+            else
+                mc = expectedModCount;
+            if (valids != null && valids.length >= hi &&
+                (i = index) >= 0 && i < (index = hi)) {
+                do {
+                    if (valids[i]) {
+                        action.accept(castKeyToGenericType(keys[i]));
+                    }
+                    ++i;
+                } while (i < hi);
+                if (modCount != mc)
+                    throw new ConcurrentModificationException();
+            }
+            if (needToProcessNullKey && primMapNullKeyValid) {
+                action.accept(null);
+                if (modCount != mc)
+                    throw new ConcurrentModificationException();
+                needToProcessNullKey = false;
+            }
+        }
+
+        public boolean tryAdvance(Consumer<? super K> action) {
+            int hi = getFence(); // force init
+            if (action == null)
+                throw new NullPointerException();
+            boolean[] valids = primMapValids;
+            Long[] keys = primMapKeys;
+            if (valids != null && valids.length >= hi && index >= 0) {
+                while (index < hi) {
+                    if (!valids[index]) {
+                        ++index;
+                    } else {
+                        action.accept(castKeyToGenericType(keys[index]));
+                        ++index;
+                        if (modCount != expectedModCount) {
+                            throw new ConcurrentModificationException();
+                        }
+                        return true;
+                    }
+                }
+            }
+            if (needToProcessNullKey && primMapNullKeyValid) {
+                action.accept(null);
+                if (modCount != expectedModCount) {
+                    throw new ConcurrentModificationException();
+                }
+                needToProcessNullKey = false;
+                return true;
+            }
+            return false;
+        }
+
+        public int characteristics() {
+            return (fence < 0 || est == size ? Spliterator.SIZED : 0) |
+                    Spliterator.DISTINCT;
+        }
+    }
+
+    final class primHashMapValueSpliterator
+        extends primHashMapSpliterator<V> {
+        primHashMapValueSpliterator(int origin, int fence, int est,
+                                    int expectedModCount, boolean needToProcessNullKey) {
+            super(origin, fence, est, expectedModCount, needToProcessNullKey);
+        }
+
+        public primHashMapValueSpliterator trySplit() {
+            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
+            return (lo >= mid) ? null :
+                    new primHashMapValueSpliterator(lo, index = mid, est >>>= 1,
+                                                    expectedModCount, false);
+        }
+
+        public void forEachRemaining(Consumer<? super V> action) {
+            int i, hi, mc;
+            if (action == null)
+                throw new NullPointerException();
+            boolean[] valids = primMapValids;
+            V[] values = primMapValues;
+            if ((hi = fence) < 0) {
+                mc = expectedModCount = modCount;
+                hi = fence = (valids == null) ? 0 : valids.length;
+            }
+            else
+                mc = expectedModCount;
+            if (valids != null && valids.length >= hi &&
+                (i = index) >= 0 && i < (index = hi)) {
+                do {
+                    if (valids[i]) {
+                        action.accept(values[i]);
+                    }
+                    ++i;
+                } while (i < hi);
+                if (modCount != mc)
+                    throw new ConcurrentModificationException();
+            }
+            if (needToProcessNullKey && primMapNullKeyValid) {
+                action.accept(primMapValOfNullKey);
+                if (modCount != mc)
+                    throw new ConcurrentModificationException();
+                needToProcessNullKey = false;
+            }
+        }
+
+        public boolean tryAdvance(Consumer<? super V> action) {
+            int hi = getFence(); // force init
+            if (action == null)
+                throw new NullPointerException();
+            boolean[] valids = primMapValids;
+            V[] values = primMapValues;
+            if (valids != null && valids.length >= hi && index >= 0) {
+                while (index < hi) {
+                    if (!valids[index]) {
+                        ++index;
+                    } else {
+                        action.accept(values[index]);
+                        ++index;
+                        if (modCount != expectedModCount)
+                            throw new ConcurrentModificationException();
+                        return true;
+                    }
+                }
+            }
+            if (needToProcessNullKey && primMapNullKeyValid) {
+                action.accept(primMapValOfNullKey);
+                if (modCount != expectedModCount)
+                    throw new ConcurrentModificationException();
+                needToProcessNullKey = false;
+                return true;
+            }
+            return false;
+        }
+
+        public int characteristics() {
+            return (fence < 0 || est == size ? Spliterator.SIZED : 0);
+        }
+    }
+
+    final class primHashMapEntrySpliterator
+        extends primHashMapSpliterator<Map.Entry<K,V>> {
+        primHashMapEntrySpliterator(int origin, int fence, int est,
+                                    int expectedModCount, boolean needToProcessNullKey) {
+            super(origin, fence, est, expectedModCount, needToProcessNullKey);
+        }
+
+        public primHashMapEntrySpliterator trySplit() {
+            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
+            return (lo >= mid) ? null :
+                    new primHashMapEntrySpliterator(lo, index = mid, est >>>= 1,
+                                                    expectedModCount, false);
+        }
+
+        public void forEachRemaining(Consumer<? super Map.Entry<K,V>> action) {
+            int i, hi, mc;
+            if (action == null)
+                throw new NullPointerException();
+            boolean[] valids = primMapValids;
+
+            if ((hi = fence) < 0) {
+                mc = expectedModCount = modCount;
+                hi = fence = (valids == null) ? 0 : valids.length;
+            }
+            else
+                mc = expectedModCount;
+            if (valids != null && valids.length >= hi &&
+                (i = index) >= 0 && i < (index = hi)) {
+                do {
+                    if (valids[i]) {
+                        action.accept(new primHashMapNode(i));
+                    }
+                    ++i;
+                } while ( i < hi);
+                if (modCount != mc)
+                    throw new ConcurrentModificationException();
+            }
+            if (needToProcessNullKey && primMapNullKeyValid) {
+                action.accept(new primHashMapNode(NULL_KEY_INDEX_FOR_RPIM_MAP));
+                if (modCount != mc)
+                    throw new ConcurrentModificationException();
+                needToProcessNullKey = false;
+            }
+        }
+
+        public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) {
+            int hi = getFence(); // force init
+            if (action == null)
+                throw new NullPointerException();
+            boolean[] valids = primMapValids;
+            if (valids != null && valids.length >= hi && index >= 0) {
+                while (index < hi) {
+                    if (!valids[index]) {
+                        ++index;
+                    }
+                    else {
+                        action.accept(new primHashMapNode(index));
+                        ++index;
+                        if (modCount != expectedModCount)
+                            throw new ConcurrentModificationException();
+                        return true;
+                    }
+                }
+            }
+            if (needToProcessNullKey && primMapNullKeyValid) {
+                action.accept(new primHashMapNode(NULL_KEY_INDEX_FOR_RPIM_MAP));
+                if (modCount != expectedModCount)
+                    throw new ConcurrentModificationException();
+                needToProcessNullKey = false;
+                return true;
+            }
+            return false;
+        }
+
+        public int characteristics() {
+            return (fence < 0 || est == size ? Spliterator.SIZED : 0) |
+                    Spliterator.DISTINCT;
+        }
+    }
+
+}
diff --git a/test/jdk/java/util/HashMap/LinkedHashMap.java b/test/jdk/java/util/HashMap/LinkedHashMap.java
new file mode 100644
index 000000000..92c1a795a
--- /dev/null
+++ b/test/jdk/java/util/HashMap/LinkedHashMap.java
@@ -0,0 +1,798 @@
+/*
+ * Copyright (c) 1997, 2020, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.util;
+
+import java.util.function.Consumer;
+import java.util.function.BiConsumer;
+import java.util.function.BiFunction;
+import java.io.IOException;
+
+/**
+ * <p>Hash table and linked list implementation of the {@code Map} interface,
+ * with predictable iteration order.  This implementation differs from
+ * {@code HashMap} in that it maintains a doubly-linked list running through
+ * all of its entries.  This linked list defines the iteration ordering,
+ * which is normally the order in which keys were inserted into the map
+ * (<i>insertion-order</i>).  Note that insertion order is not affected
+ * if a key is <i>re-inserted</i> into the map.  (A key {@code k} is
+ * reinserted into a map {@code m} if {@code m.put(k, v)} is invoked when
+ * {@code m.containsKey(k)} would return {@code true} immediately prior to
+ * the invocation.)
+ *
+ * <p>This implementation spares its clients from the unspecified, generally
+ * chaotic ordering provided by {@link HashMap} (and {@link Hashtable}),
+ * without incurring the increased cost associated with {@link TreeMap}.  It
+ * can be used to produce a copy of a map that has the same order as the
+ * original, regardless of the original map's implementation:
+ * <pre>{@code
+ *     void foo(Map<String, Integer> m) {
+ *         Map<String, Integer> copy = new LinkedHashMap<>(m);
+ *         ...
+ *     }
+ * }</pre>
+ * This technique is particularly useful if a module takes a map on input,
+ * copies it, and later returns results whose order is determined by that of
+ * the copy.  (Clients generally appreciate having things returned in the same
+ * order they were presented.)
+ *
+ * <p>A special {@link #LinkedHashMap(int,float,boolean) constructor} is
+ * provided to create a linked hash map whose order of iteration is the order
+ * in which its entries were last accessed, from least-recently accessed to
+ * most-recently (<i>access-order</i>).  This kind of map is well-suited to
+ * building LRU caches.  Invoking the {@code put}, {@code putIfAbsent},
+ * {@code get}, {@code getOrDefault}, {@code compute}, {@code computeIfAbsent},
+ * {@code computeIfPresent}, or {@code merge} methods results
+ * in an access to the corresponding entry (assuming it exists after the
+ * invocation completes). The {@code replace} methods only result in an access
+ * of the entry if the value is replaced.  The {@code putAll} method generates one
+ * entry access for each mapping in the specified map, in the order that
+ * key-value mappings are provided by the specified map's entry set iterator.
+ * <i>No other methods generate entry accesses.</i>  In particular, operations
+ * on collection-views do <i>not</i> affect the order of iteration of the
+ * backing map.
+ *
+ * <p>The {@link #removeEldestEntry(Map.Entry)} method may be overridden to
+ * impose a policy for removing stale mappings automatically when new mappings
+ * are added to the map.
+ *
+ * <p>This class provides all of the optional {@code Map} operations, and
+ * permits null elements.  Like {@code HashMap}, it provides constant-time
+ * performance for the basic operations ({@code add}, {@code contains} and
+ * {@code remove}), assuming the hash function disperses elements
+ * properly among the buckets.  Performance is likely to be just slightly
+ * below that of {@code HashMap}, due to the added expense of maintaining the
+ * linked list, with one exception: Iteration over the collection-views
+ * of a {@code LinkedHashMap} requires time proportional to the <i>size</i>
+ * of the map, regardless of its capacity.  Iteration over a {@code HashMap}
+ * is likely to be more expensive, requiring time proportional to its
+ * <i>capacity</i>.
+ *
+ * <p>A linked hash map has two parameters that affect its performance:
+ * <i>initial capacity</i> and <i>load factor</i>.  They are defined precisely
+ * as for {@code HashMap}.  Note, however, that the penalty for choosing an
+ * excessively high value for initial capacity is less severe for this class
+ * than for {@code HashMap}, as iteration times for this class are unaffected
+ * by capacity.
+ *
+ * <p><strong>Note that this implementation is not synchronized.</strong>
+ * If multiple threads access a linked hash map concurrently, and at least
+ * one of the threads modifies the map structurally, it <em>must</em> be
+ * synchronized externally.  This is typically accomplished by
+ * synchronizing on some object that naturally encapsulates the map.
+ *
+ * If no such object exists, the map should be "wrapped" using the
+ * {@link Collections#synchronizedMap Collections.synchronizedMap}
+ * method.  This is best done at creation time, to prevent accidental
+ * unsynchronized access to the map:<pre>
+ *   Map m = Collections.synchronizedMap(new LinkedHashMap(...));</pre>
+ *
+ * A structural modification is any operation that adds or deletes one or more
+ * mappings or, in the case of access-ordered linked hash maps, affects
+ * iteration order.  In insertion-ordered linked hash maps, merely changing
+ * the value associated with a key that is already contained in the map is not
+ * a structural modification.  <strong>In access-ordered linked hash maps,
+ * merely querying the map with {@code get} is a structural modification.
+ * </strong>)
+ *
+ * <p>The iterators returned by the {@code iterator} method of the collections
+ * returned by all of this class's collection view methods are
+ * <em>fail-fast</em>: if the map is structurally modified at any time after
+ * the iterator is created, in any way except through the iterator's own
+ * {@code remove} method, the iterator will throw a {@link
+ * ConcurrentModificationException}.  Thus, in the face of concurrent
+ * modification, the iterator fails quickly and cleanly, rather than risking
+ * arbitrary, non-deterministic behavior at an undetermined time in the future.
+ *
+ * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
+ * as it is, generally speaking, impossible to make any hard guarantees in the
+ * presence of unsynchronized concurrent modification.  Fail-fast iterators
+ * throw {@code ConcurrentModificationException} on a best-effort basis.
+ * Therefore, it would be wrong to write a program that depended on this
+ * exception for its correctness:   <i>the fail-fast behavior of iterators
+ * should be used only to detect bugs.</i>
+ *
+ * <p>The spliterators returned by the spliterator method of the collections
+ * returned by all of this class's collection view methods are
+ * <em><a href="Spliterator.html#binding">late-binding</a></em>,
+ * <em>fail-fast</em>, and additionally report {@link Spliterator#ORDERED}.
+ *
+ * <p>This class is a member of the
+ * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
+ * Java Collections Framework</a>.
+ *
+ * @implNote
+ * The spliterators returned by the spliterator method of the collections
+ * returned by all of this class's collection view methods are created from
+ * the iterators of the corresponding collections.
+ *
+ * @param <K> the type of keys maintained by this map
+ * @param <V> the type of mapped values
+ *
+ * @author  Josh Bloch
+ * @see     Object#hashCode()
+ * @see     Collection
+ * @see     Map
+ * @see     HashMap
+ * @see     TreeMap
+ * @see     Hashtable
+ * @since   1.4
+ */
+public class LinkedHashMap<K,V>
+    extends HashMap<K,V>
+    implements Map<K,V>
+{
+
+    /*
+     * Implementation note.  A previous version of this class was
+     * internally structured a little differently. Because superclass
+     * HashMap now uses trees for some of its nodes, class
+     * LinkedHashMap.Entry is now treated as intermediary node class
+     * that can also be converted to tree form. The name of this
+     * class, LinkedHashMap.Entry, is confusing in several ways in its
+     * current context, but cannot be changed.  Otherwise, even though
+     * it is not exported outside this package, some existing source
+     * code is known to have relied on a symbol resolution corner case
+     * rule in calls to removeEldestEntry that suppressed compilation
+     * errors due to ambiguous usages. So, we keep the name to
+     * preserve unmodified compilability.
+     *
+     * The changes in node classes also require using two fields
+     * (head, tail) rather than a pointer to a header node to maintain
+     * the doubly-linked before/after list. This class also
+     * previously used a different style of callback methods upon
+     * access, insertion, and removal.
+     */
+
+    /**
+     * HashMap.Node subclass for normal LinkedHashMap entries.
+     */
+    static class Entry<K,V> extends HashMap.Node<K,V> {
+        Entry<K,V> before, after;
+        Entry(int hash, K key, V value, Node<K,V> next) {
+            super(hash, key, value, next);
+        }
+    }
+
+    @java.io.Serial
+    private static final long serialVersionUID = 3801124242820219131L;
+
+    /**
+     * The head (eldest) of the doubly linked list.
+     */
+    transient LinkedHashMap.Entry<K,V> head;
+
+    /**
+     * The tail (youngest) of the doubly linked list.
+     */
+    transient LinkedHashMap.Entry<K,V> tail;
+
+    /**
+     * The iteration ordering method for this linked hash map: {@code true}
+     * for access-order, {@code false} for insertion-order.
+     *
+     * @serial
+     */
+    final boolean accessOrder;
+
+    // internal utilities
+
+    // link at the end of list
+    private void linkNodeLast(LinkedHashMap.Entry<K,V> p) {
+        LinkedHashMap.Entry<K,V> last = tail;
+        tail = p;
+        if (last == null)
+            head = p;
+        else {
+            p.before = last;
+            last.after = p;
+        }
+    }
+
+    // apply src's links to dst
+    private void transferLinks(LinkedHashMap.Entry<K,V> src,
+                               LinkedHashMap.Entry<K,V> dst) {
+        LinkedHashMap.Entry<K,V> b = dst.before = src.before;
+        LinkedHashMap.Entry<K,V> a = dst.after = src.after;
+        if (b == null)
+            head = dst;
+        else
+            b.after = dst;
+        if (a == null)
+            tail = dst;
+        else
+            a.before = dst;
+    }
+
+    // overrides of HashMap hook methods
+
+    void reinitialize() {
+        super.reinitialize();
+        disablePrimHashMap();
+        head = tail = null;
+    }
+
+    Node<K,V> newNode(int hash, K key, V value, Node<K,V> e) {
+        LinkedHashMap.Entry<K,V> p =
+            new LinkedHashMap.Entry<>(hash, key, value, e);
+        linkNodeLast(p);
+        return p;
+    }
+
+    Node<K,V> replacementNode(Node<K,V> p, Node<K,V> next) {
+        LinkedHashMap.Entry<K,V> q = (LinkedHashMap.Entry<K,V>)p;
+        LinkedHashMap.Entry<K,V> t =
+            new LinkedHashMap.Entry<>(q.hash, q.key, q.value, next);
+        transferLinks(q, t);
+        return t;
+    }
+
+    TreeNode<K,V> newTreeNode(int hash, K key, V value, Node<K,V> next) {
+        TreeNode<K,V> p = new TreeNode<>(hash, key, value, next);
+        linkNodeLast(p);
+        return p;
+    }
+
+    TreeNode<K,V> replacementTreeNode(Node<K,V> p, Node<K,V> next) {
+        LinkedHashMap.Entry<K,V> q = (LinkedHashMap.Entry<K,V>)p;
+        TreeNode<K,V> t = new TreeNode<>(q.hash, q.key, q.value, next);
+        transferLinks(q, t);
+        return t;
+    }
+
+    void afterNodeRemoval(Node<K,V> e) { // unlink
+        LinkedHashMap.Entry<K,V> p =
+            (LinkedHashMap.Entry<K,V>)e, b = p.before, a = p.after;
+        p.before = p.after = null;
+        if (b == null)
+            head = a;
+        else
+            b.after = a;
+        if (a == null)
+            tail = b;
+        else
+            a.before = b;
+    }
+
+    void afterNodeInsertion(boolean evict) { // possibly remove eldest
+        LinkedHashMap.Entry<K,V> first;
+        if (evict && (first = head) != null && removeEldestEntry(first)) {
+            K key = first.key;
+            removeNode(hash(key), key, null, false, true);
+        }
+    }
+
+    void afterNodeAccess(Node<K,V> e) { // move node to last
+        LinkedHashMap.Entry<K,V> last;
+        if (accessOrder && (last = tail) != e) {
+            LinkedHashMap.Entry<K,V> p =
+                (LinkedHashMap.Entry<K,V>)e, b = p.before, a = p.after;
+            p.after = null;
+            if (b == null)
+                head = a;
+            else
+                b.after = a;
+            if (a != null)
+                a.before = b;
+            else
+                last = b;
+            if (last == null)
+                head = p;
+            else {
+                p.before = last;
+                last.after = p;
+            }
+            tail = p;
+            ++modCount;
+        }
+    }
+
+    void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
+        for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
+            s.writeObject(e.key);
+            s.writeObject(e.value);
+        }
+    }
+
+    /**
+     * Constructs an empty insertion-ordered {@code LinkedHashMap} instance
+     * with the specified initial capacity and load factor.
+     *
+     * @param  initialCapacity the initial capacity
+     * @param  loadFactor      the load factor
+     * @throws IllegalArgumentException if the initial capacity is negative
+     *         or the load factor is nonpositive
+     */
+    public LinkedHashMap(int initialCapacity, float loadFactor) {
+        super(initialCapacity, loadFactor);
+        disablePrimHashMap();
+        accessOrder = false;
+    }
+
+    /**
+     * Constructs an empty insertion-ordered {@code LinkedHashMap} instance
+     * with the specified initial capacity and a default load factor (0.75).
+     *
+     * @param  initialCapacity the initial capacity
+     * @throws IllegalArgumentException if the initial capacity is negative
+     */
+    public LinkedHashMap(int initialCapacity) {
+        super(initialCapacity);
+        disablePrimHashMap();
+        accessOrder = false;
+    }
+
+    /**
+     * Constructs an empty insertion-ordered {@code LinkedHashMap} instance
+     * with the default initial capacity (16) and load factor (0.75).
+     */
+    public LinkedHashMap() {
+        super();
+        disablePrimHashMap();
+        accessOrder = false;
+    }
+
+    /**
+     * Constructs an insertion-ordered {@code LinkedHashMap} instance with
+     * the same mappings as the specified map.  The {@code LinkedHashMap}
+     * instance is created with a default load factor (0.75) and an initial
+     * capacity sufficient to hold the mappings in the specified map.
+     *
+     * @param  m the map whose mappings are to be placed in this map
+     * @throws NullPointerException if the specified map is null
+     */
+    public LinkedHashMap(Map<? extends K, ? extends V> m) {
+        super();
+        disablePrimHashMap();
+        accessOrder = false;
+        putMapEntries(m, false);
+    }
+
+    /**
+     * Constructs an empty {@code LinkedHashMap} instance with the
+     * specified initial capacity, load factor and ordering mode.
+     *
+     * @param  initialCapacity the initial capacity
+     * @param  loadFactor      the load factor
+     * @param  accessOrder     the ordering mode - {@code true} for
+     *         access-order, {@code false} for insertion-order
+     * @throws IllegalArgumentException if the initial capacity is negative
+     *         or the load factor is nonpositive
+     */
+    public LinkedHashMap(int initialCapacity,
+                         float loadFactor,
+                         boolean accessOrder) {
+        super(initialCapacity, loadFactor);
+        disablePrimHashMap();
+        this.accessOrder = accessOrder;
+    }
+
+
+    /**
+     * Returns {@code true} if this map maps one or more keys to the
+     * specified value.
+     *
+     * @param value value whose presence in this map is to be tested
+     * @return {@code true} if this map maps one or more keys to the
+     *         specified value
+     */
+    public boolean containsValue(Object value) {
+        for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
+            V v = e.value;
+            if (v == value || (value != null && value.equals(v)))
+                return true;
+        }
+        return false;
+    }
+
+    /**
+     * Returns the value to which the specified key is mapped,
+     * or {@code null} if this map contains no mapping for the key.
+     *
+     * <p>More formally, if this map contains a mapping from a key
+     * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
+     * key.equals(k))}, then this method returns {@code v}; otherwise
+     * it returns {@code null}.  (There can be at most one such mapping.)
+     *
+     * <p>A return value of {@code null} does not <i>necessarily</i>
+     * indicate that the map contains no mapping for the key; it's also
+     * possible that the map explicitly maps the key to {@code null}.
+     * The {@link #containsKey containsKey} operation may be used to
+     * distinguish these two cases.
+     */
+    public V get(Object key) {
+        Node<K,V> e;
+        if ((e = getNode(key)) == null)
+            return null;
+        if (accessOrder)
+            afterNodeAccess(e);
+        return e.value;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public V getOrDefault(Object key, V defaultValue) {
+       Node<K,V> e;
+       if ((e = getNode(key)) == null)
+           return defaultValue;
+       if (accessOrder)
+           afterNodeAccess(e);
+       return e.value;
+   }
+
+    /**
+     * {@inheritDoc}
+     */
+    public void clear() {
+        super.clear();
+        head = tail = null;
+    }
+
+    /**
+     * Returns {@code true} if this map should remove its eldest entry.
+     * This method is invoked by {@code put} and {@code putAll} after
+     * inserting a new entry into the map.  It provides the implementor
+     * with the opportunity to remove the eldest entry each time a new one
+     * is added.  This is useful if the map represents a cache: it allows
+     * the map to reduce memory consumption by deleting stale entries.
+     *
+     * <p>Sample use: this override will allow the map to grow up to 100
+     * entries and then delete the eldest entry each time a new entry is
+     * added, maintaining a steady state of 100 entries.
+     * <pre>
+     *     private static final int MAX_ENTRIES = 100;
+     *
+     *     protected boolean removeEldestEntry(Map.Entry eldest) {
+     *        return size() &gt; MAX_ENTRIES;
+     *     }
+     * </pre>
+     *
+     * <p>This method typically does not modify the map in any way,
+     * instead allowing the map to modify itself as directed by its
+     * return value.  It <i>is</i> permitted for this method to modify
+     * the map directly, but if it does so, it <i>must</i> return
+     * {@code false} (indicating that the map should not attempt any
+     * further modification).  The effects of returning {@code true}
+     * after modifying the map from within this method are unspecified.
+     *
+     * <p>This implementation merely returns {@code false} (so that this
+     * map acts like a normal map - the eldest element is never removed).
+     *
+     * @param    eldest The least recently inserted entry in the map, or if
+     *           this is an access-ordered map, the least recently accessed
+     *           entry.  This is the entry that will be removed it this
+     *           method returns {@code true}.  If the map was empty prior
+     *           to the {@code put} or {@code putAll} invocation resulting
+     *           in this invocation, this will be the entry that was just
+     *           inserted; in other words, if the map contains a single
+     *           entry, the eldest entry is also the newest.
+     * @return   {@code true} if the eldest entry should be removed
+     *           from the map; {@code false} if it should be retained.
+     */
+    protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
+        return false;
+    }
+
+    /**
+     * Returns a {@link Set} view of the keys contained in this map.
+     * The set is backed by the map, so changes to the map are
+     * reflected in the set, and vice-versa.  If the map is modified
+     * while an iteration over the set is in progress (except through
+     * the iterator's own {@code remove} operation), the results of
+     * the iteration are undefined.  The set supports element removal,
+     * which removes the corresponding mapping from the map, via the
+     * {@code Iterator.remove}, {@code Set.remove},
+     * {@code removeAll}, {@code retainAll}, and {@code clear}
+     * operations.  It does not support the {@code add} or {@code addAll}
+     * operations.
+     * Its {@link Spliterator} typically provides faster sequential
+     * performance but much poorer parallel performance than that of
+     * {@code HashMap}.
+     *
+     * @return a set view of the keys contained in this map
+     */
+    public Set<K> keySet() {
+        Set<K> ks = keySet;
+        if (ks == null) {
+            ks = new LinkedKeySet();
+            keySet = ks;
+        }
+        return ks;
+    }
+
+    @Override
+    final <T> T[] keysToArray(T[] a) {
+        Object[] r = a;
+        int idx = 0;
+        for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
+            r[idx++] = e.key;
+        }
+        return a;
+    }
+
+    @Override
+    final <T> T[] valuesToArray(T[] a) {
+        Object[] r = a;
+        int idx = 0;
+        for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
+            r[idx++] = e.value;
+        }
+        return a;
+    }
+
+    final class LinkedKeySet extends AbstractSet<K> {
+        public final int size()                 { return size; }
+        public final void clear()               { LinkedHashMap.this.clear(); }
+        public final Iterator<K> iterator() {
+            return new LinkedKeyIterator();
+        }
+        public final boolean contains(Object o) { return containsKey(o); }
+        public final boolean remove(Object key) {
+            return removeNode(hash(key), key, null, false, true) != null;
+        }
+        public final Spliterator<K> spliterator()  {
+            return Spliterators.spliterator(this, Spliterator.SIZED |
+                                            Spliterator.ORDERED |
+                                            Spliterator.DISTINCT);
+        }
+
+        public Object[] toArray() {
+            return keysToArray(new Object[size]);
+        }
+
+        public <T> T[] toArray(T[] a) {
+            return keysToArray(prepareArray(a));
+        }
+
+        public final void forEach(Consumer<? super K> action) {
+            if (action == null)
+                throw new NullPointerException();
+            int mc = modCount;
+            for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
+                action.accept(e.key);
+            if (modCount != mc)
+                throw new ConcurrentModificationException();
+        }
+    }
+
+    /**
+     * Returns a {@link Collection} view of the values contained in this map.
+     * The collection is backed by the map, so changes to the map are
+     * reflected in the collection, and vice-versa.  If the map is
+     * modified while an iteration over the collection is in progress
+     * (except through the iterator's own {@code remove} operation),
+     * the results of the iteration are undefined.  The collection
+     * supports element removal, which removes the corresponding
+     * mapping from the map, via the {@code Iterator.remove},
+     * {@code Collection.remove}, {@code removeAll},
+     * {@code retainAll} and {@code clear} operations.  It does not
+     * support the {@code add} or {@code addAll} operations.
+     * Its {@link Spliterator} typically provides faster sequential
+     * performance but much poorer parallel performance than that of
+     * {@code HashMap}.
+     *
+     * @return a view of the values contained in this map
+     */
+    public Collection<V> values() {
+        Collection<V> vs = values;
+        if (vs == null) {
+            vs = new LinkedValues();
+            values = vs;
+        }
+        return vs;
+    }
+
+    final class LinkedValues extends AbstractCollection<V> {
+        public final int size()                 { return size; }
+        public final void clear()               { LinkedHashMap.this.clear(); }
+        public final Iterator<V> iterator() {
+            return new LinkedValueIterator();
+        }
+        public final boolean contains(Object o) { return containsValue(o); }
+        public final Spliterator<V> spliterator() {
+            return Spliterators.spliterator(this, Spliterator.SIZED |
+                                            Spliterator.ORDERED);
+        }
+
+        public Object[] toArray() {
+            return valuesToArray(new Object[size]);
+        }
+
+        public <T> T[] toArray(T[] a) {
+            return valuesToArray(prepareArray(a));
+        }
+
+        public final void forEach(Consumer<? super V> action) {
+            if (action == null)
+                throw new NullPointerException();
+            int mc = modCount;
+            for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
+                action.accept(e.value);
+            if (modCount != mc)
+                throw new ConcurrentModificationException();
+        }
+    }
+
+    /**
+     * Returns a {@link Set} view of the mappings contained in this map.
+     * The set is backed by the map, so changes to the map are
+     * reflected in the set, and vice-versa.  If the map is modified
+     * while an iteration over the set is in progress (except through
+     * the iterator's own {@code remove} operation, or through the
+     * {@code setValue} operation on a map entry returned by the
+     * iterator) the results of the iteration are undefined.  The set
+     * supports element removal, which removes the corresponding
+     * mapping from the map, via the {@code Iterator.remove},
+     * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
+     * {@code clear} operations.  It does not support the
+     * {@code add} or {@code addAll} operations.
+     * Its {@link Spliterator} typically provides faster sequential
+     * performance but much poorer parallel performance than that of
+     * {@code HashMap}.
+     *
+     * @return a set view of the mappings contained in this map
+     */
+    public Set<Map.Entry<K,V>> entrySet() {
+        Set<Map.Entry<K,V>> es;
+        return (es = entrySet) == null ? (entrySet = new LinkedEntrySet()) : es;
+    }
+
+    final class LinkedEntrySet extends AbstractSet<Map.Entry<K,V>> {
+        public final int size()                 { return size; }
+        public final void clear()               { LinkedHashMap.this.clear(); }
+        public final Iterator<Map.Entry<K,V>> iterator() {
+            return new LinkedEntryIterator();
+        }
+        public final boolean contains(Object o) {
+            if (!(o instanceof Map.Entry<?, ?> e))
+                return false;
+            Object key = e.getKey();
+            Node<K,V> candidate = getNode(key);
+            return candidate != null && candidate.equals(e);
+        }
+        public final boolean remove(Object o) {
+            if (o instanceof Map.Entry<?, ?> e) {
+                Object key = e.getKey();
+                Object value = e.getValue();
+                return removeNode(hash(key), key, value, true, true) != null;
+            }
+            return false;
+        }
+        public final Spliterator<Map.Entry<K,V>> spliterator() {
+            return Spliterators.spliterator(this, Spliterator.SIZED |
+                                            Spliterator.ORDERED |
+                                            Spliterator.DISTINCT);
+        }
+        public final void forEach(Consumer<? super Map.Entry<K,V>> action) {
+            if (action == null)
+                throw new NullPointerException();
+            int mc = modCount;
+            for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
+                action.accept(e);
+            if (modCount != mc)
+                throw new ConcurrentModificationException();
+        }
+    }
+
+    // Map overrides
+
+    public void forEach(BiConsumer<? super K, ? super V> action) {
+        if (action == null)
+            throw new NullPointerException();
+        int mc = modCount;
+        for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
+            action.accept(e.key, e.value);
+        if (modCount != mc)
+            throw new ConcurrentModificationException();
+    }
+
+    public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
+        if (function == null)
+            throw new NullPointerException();
+        int mc = modCount;
+        for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
+            e.value = function.apply(e.key, e.value);
+        if (modCount != mc)
+            throw new ConcurrentModificationException();
+    }
+
+    // Iterators
+
+    abstract class LinkedHashIterator {
+        LinkedHashMap.Entry<K,V> next;
+        LinkedHashMap.Entry<K,V> current;
+        int expectedModCount;
+
+        LinkedHashIterator() {
+            next = head;
+            expectedModCount = modCount;
+            current = null;
+        }
+
+        public final boolean hasNext() {
+            return next != null;
+        }
+
+        final LinkedHashMap.Entry<K,V> nextNode() {
+            LinkedHashMap.Entry<K,V> e = next;
+            if (modCount != expectedModCount)
+                throw new ConcurrentModificationException();
+            if (e == null)
+                throw new NoSuchElementException();
+            current = e;
+            next = e.after;
+            return e;
+        }
+
+        public final void remove() {
+            Node<K,V> p = current;
+            if (p == null)
+                throw new IllegalStateException();
+            if (modCount != expectedModCount)
+                throw new ConcurrentModificationException();
+            current = null;
+            removeNode(p.hash, p.key, null, false, false);
+            expectedModCount = modCount;
+        }
+    }
+
+    final class LinkedKeyIterator extends LinkedHashIterator
+        implements Iterator<K> {
+        public final K next() { return nextNode().getKey(); }
+    }
+
+    final class LinkedValueIterator extends LinkedHashIterator
+        implements Iterator<V> {
+        public final V next() { return nextNode().value; }
+    }
+
+    final class LinkedEntryIterator extends LinkedHashIterator
+        implements Iterator<Map.Entry<K,V>> {
+        public final Map.Entry<K,V> next() { return nextNode(); }
+    }
+
+
+}
-- 
2.22.0