用java实现一个windows系统自带计算器

下面是用 Java Swing 实现的一个简单的 Windows 计算器：

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public class Calculator extends JFrame implements ActionListener {

    private static final long serialVersionUID = 1L;

    // 显示运算结果的文本框
    private JTextField resultText;

    // 数字按钮
    private JButton[] numberButtons = new JButton[10];

    // 运算符按钮
    private JButton addButton, subButton, mulButton, divButton, equalButton, dotButton;

    // 存储数字和运算符的字符串
    private String num1 = "", num2 = "", operator = "";

    public Calculator() {
        initUI();
    }

    private void initUI() {
        setTitle("计算器");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setResizable(false);

        // 显示结果的文本框
        resultText = new JTextField(12);
        resultText.setEditable(false);
        resultText.setHorizontalAlignment(JTextField.RIGHT);

        // 数字按钮
        for (int i = 0; i < 10; i++) {
            numberButtons[i] = new JButton(String.valueOf(i));
            numberButtons[i].addActionListener(this);
        }

        // 运算符按钮
        addButton = new JButton("+");
        subButton = new JButton("-");
        mulButton = new JButton("*");
        divButton = new JButton("/");
        equalButton = new JButton("=");
        dotButton = new JButton(".");
        addButton.addActionListener(this);
        subButton.addActionListener(this);
        mulButton.addActionListener(this);
        divButton.addActionListener(this);
        equalButton.addActionListener(this);
        dotButton.addActionListener(this);

        // 将数字按钮放在面板上
        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new GridLayout(4, 3));
        for (int i = 1; i < 10; i++) {
            buttonPanel.add(numberButtons[i]);
        }
        buttonPanel.add(new JPanel());
        buttonPanel.add(numberButtons[0]);
        buttonPanel.add(dotButton);

        // 将运算符按钮放在面板上
        JPanel operatorPanel = new JPanel();
        operatorPanel.setLayout(new GridLayout(2, 2));
        operatorPanel.add(addButton);
        operatorPanel.add(subButton);
        operatorPanel.add(mulButton);
        operatorPanel.add(divButton);

        // 将等号按钮放在面板上
        JPanel equalPanel = new JPanel();
        equalPanel.setLayout(new FlowLayout());
        equalPanel.add(equalButton);

        // 将文本框和按钮面板放在顶层面板上
        JPanel topPanel = new JPanel();
        topPanel.setLayout(new BorderLayout());
        topPanel.add(resultText, BorderLayout.NORTH);
        topPanel.add(buttonPanel, BorderLayout.CENTER);

        // 将运算符面板和等号面板放在底层面板上
        JPanel botPanel = new JPanel();
        botPanel.setLayout(new BorderLayout());
        botPanel.add(operatorPanel, BorderLayout.CENTER);
        botPanel.add(equalPanel, BorderLayout.EAST);

        // 将顶层面板和底层面板放在窗口上
        setLayout(new BorderLayout());
        add(topPanel, BorderLayout.NORTH);
        add(botPanel, BorderLayout.CENTER);

        pack();
        setLocationRelativeTo(null);
    }

    public static void main(String[] args) {
        Calculator calculator = new Calculator();
        calculator.setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();
        switch (command) {
            case "0":
            case "1":
            case "2":
            case "3":
            case "4":
            case "5":
            case "6":
            case "7":
            case "8":
            case "9":
                if (operator.isEmpty()) {
                    num1 += command;
                    resultText.setText(num1);
                } else {
                    num2 += command;
                    resultText.setText(num2);
                }
                break;
            case "+":
            case "-":
            case "*":
            case "/":
                operator = command;
                break;
            case ".":
                if (operator.isEmpty()) {
                    if (!num1.contains(".")) {
                        num1 += ".";
                        resultText.setText(num1);
                    }
                } else {
                    if (!num2.contains(".")) {
                        num2 += ".";
                        resultText.setText(num2);
                    }
                }
                break;
            case "=":
                if (!num1.isEmpty() && !num2.isEmpty() && !operator.isEmpty()) {
                    double n1 = Double.parseDouble(num1);
                    double n2 = Double.parseDouble(num2);
                    double result = 0;
                    switch (operator) {
                        case "+":
                            result = n1 + n2;
                            break;
                        case "-":
                            result = n1 - n2;
                            break;
                        case "*":
                            result = n1 * n2;
                            break;
                        case "/":
                            if (n2 == 0) {
                                resultText.setText("除数不能为0");
                                return;
                            }
                            result = n1 / n2;
                            break;
                    }
                    num1 = String.valueOf(result);
                    num2 = "";
                    operator = "";
                    resultText.setText(num1);
                }
                break;
        }
    }
}

运行程序后，会弹出一个窗口，里面有数字按钮、运算符按钮和一个文本框，用户可以点击按钮输入数字和选择运算符来进行计算。