diff --git a/src/java2020spring/calculator b/src/java2020spring/calculator
new file mode 100644
index 0000000000000000000000000000000000000000..16c388a01b4bb83958a56d53e0536ad502367514
--- /dev/null
+++ b/src/java2020spring/calculator
@@ -0,0 +1,177 @@
+import java.awt.*;
+import java.awt.event.*;
+import javax.swing.*;
+
+public class standard extends JFrame implements ActionListener {
+	private final String[] KEYS = { "%", ".","sqrt", "9", "8", "7","6", "5", "4", "3", "2", "1", "0", "+", "-","*","/","=","1/x","MC","MR","MS","M+" };
+	private final String[] COMMAND = {"Back", "C" };
+	private JButton keys[] = new JButton[KEYS.length];
+	private JButton commands[] = new JButton[COMMAND.length];
+	private JTextField resultText = new JTextField("0");
+	private boolean firstDigit = true;
+	private double resultNum = 0.0;
+	private String operator = "=";
+	private boolean operateValidFlag = true;
+	StringBuffer sb = new StringBuffer();
+	String vl = null;
+	public standard() {
+		setTitle("标准型");
+		this.setBackground(Color.LIGHT_GRAY);
+		this.setTitle("标准计算器");
+		this.setLocation(500, 300);
+		this.setSize(500, 500);
+		this.setResizable(false);
+		JMenuBar menuBar = new JMenuBar();
+		setJMenuBar(menuBar);
+		resultText.setHorizontalAlignment(JTextField.RIGHT);
+		resultText.setBackground(Color.white);
+		resultText.setFont(new Font("TimesRoman",Font.BOLD,46));
+		JPanel PPanel = new JPanel();
+		PPanel.setLayout(new GridLayout(5, 4, 3, 3));
+		for (int i = 0; i < COMMAND.length; i++) {
+			commands[i] = new JButton(COMMAND[i]);
+			PPanel.add(commands[i]);
+			commands[i].setFont(new Font("Courir",Font.PLAIN,20));
+		}
+		for (int i = 0; i < KEYS.length; i++) {
+			keys[i] = new JButton(KEYS[i]);
+			PPanel.add(keys[i]);
+			keys[i].setFont(new Font("Courir",Font.ITALIC,20));
+		}
+		JPanel panel1 = new JPanel();
+		panel1.setLayout(new BorderLayout(3,3));
+		panel1.add("Center", PPanel);
+		JPanel top = new JPanel();
+		top.setLayout(new BorderLayout());
+		top.add("Center", resultText);
+		
+		getContentPane().setLayout(new BorderLayout(3, 5));
+		getContentPane().add("North", top);
+		getContentPane().add("Center", panel1);
+		for (int i = 0; i < KEYS.length; i++) {
+			keys[i].addActionListener(this);
+		}
+		for (int i = 0; i < COMMAND.length; i++) {
+			commands[i].addActionListener(this);
+		}
+		
+	}
+	
+	public void actionPerformed(ActionEvent e) {
+		String label = e.getActionCommand();
+		if (label.equals(COMMAND[0])) {
+			handleBack();
+		} 
+		else if (label.equals(COMMAND[1])) {
+			handleC();
+		} 
+		else if ("0123456789.".indexOf(label) >= 0) {
+			handleNumber(label);
+		} 
+		else
+			handleOperator(label);
+	}
+	
+	private void handleBack() {
+		String text = resultText.getText();
+		int i = text.length();
+		if (i > 0) {
+			text = text.substring(0, i - 1);
+			if (text.length() == 0) {
+				resultText.setText("0");
+				firstDigit = true;
+				operator = "=";
+			}
+			else
+				resultText.setText(text);
+		}
+	}
+
+	private void handleNumber(String key) {
+		if (firstDigit) {
+			resultText.setText(key);
+		}
+		else if ((key.equals(".")) && (resultText.getText().indexOf(".") < 0)) {
+			resultText.setText(resultText.getText() + ".");
+		}
+		else if (!key.equals(".")) {
+			resultText.setText(resultText.getText() + key);
+		}
+		firstDigit = false;
+	}
+	
+	private void handleC() {
+		resultText.setText("0");
+		firstDigit = true;
+		operator = "=";
+	}
+	
+	private void handleOperator(String key) {
+		if (operator.equals("/")) {
+			if (getNumberFromText() == 0.0) {
+				operateValidFlag = false;
+				resultText.setText("除数不能为零");
+			}
+			else 
+				resultNum /= getNumberFromText();
+		} 
+		else if (operator.equals("1/x")) {
+			if (resultNum == 0.0) {
+				operateValidFlag = false;
+				resultText.setText("零没有倒数");
+			}
+			else
+				resultNum = 1 / resultNum;
+			}
+		else if (operator.equals("+")) {
+			resultNum += getNumberFromText();
+		}
+		else if (operator.equals("-")) {
+			resultNum -= getNumberFromText();
+		}
+		else if (operator.equals("*")) {
+			resultNum *= getNumberFromText();
+		}
+		else if (operator.equals("sqrt")) {
+			resultNum = Math.sqrt(resultNum);
+		}
+		else if (operator.equals("=")) {
+			resultNum = getNumberFromText();
+		}
+		else if (operator.contentEquals("%")) {
+			while(resultNum>=getNumberFromText()) {
+				resultNum -= getNumberFromText();
+			}
+		}
+		else if (operator.contentEquals("MC")) {
+			resultNum = 0;
+		}
+		if (operateValidFlag) {
+			long t1;
+			double t2;
+			t1 = (long) resultNum;
+			t2 = resultNum - t1;
+			if (t2 == 0) {
+				resultText.setText(String.valueOf(t1));
+			}
+			else {
+				resultText.setText(String.valueOf(resultNum));
+			}
+		}
+		operator = key;
+		firstDigit = true;
+		operateValidFlag = true;
+	}
+
+	private double getNumberFromText() {
+		double result = 0;
+		try {
+			result = Double.valueOf(resultText.getText()).doubleValue();
+		} catch (NumberFormatException e) {}
+		return result;
+	}
+	
+	public static void main(String args[]) {
+		standard application = new standard();
+		application.setVisible(true);
+		application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
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