import javax.swing.; import java.awt.; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.util.Stack;

public class Calculator extends JFrame implements ActionListener {

private static final long serialVersionUID = 1L;
private JTextField inputField; // 显示输入和输出的文本框
private JButton button1, button2, button3, button4, button5;
private JButton button6, button7, button8, button9, button0;
private JButton buttonAdd, buttonSub, buttonMul, buttonDiv;
private JButton buttonSqrt, buttonFactorial, buttonClear, buttonEqual;

private StringBuilder input = new StringBuilder(); // 计算器输入的内容

public Calculator() {
    super("Calculator"); // 设置标题

    Container container = getContentPane();
    container.setLayout(new BorderLayout()); // 设置布局管理器

    // 初始化组件
    inputField = new JTextField();
    inputField.setEditable(false);
    inputField.setHorizontalAlignment(JTextField.RIGHT);
    container.add(inputField, BorderLayout.NORTH);

    JPanel buttonPanel = new JPanel();
    buttonPanel.setLayout(new GridLayout(4, 4));

    button7 = new JButton("7");
    button7.addActionListener(this);
    buttonPanel.add(button7);

    button8 = new JButton("8");
    button8.addActionListener(this);
    buttonPanel.add(button8);

    button9 = new JButton("9");
    button9.addActionListener(this);
    buttonPanel.add(button9);

    buttonDiv = new JButton("/");
    buttonDiv.addActionListener(this);
    buttonPanel.add(buttonDiv);

    button4 = new JButton("4");
    button4.addActionListener(this);
    buttonPanel.add(button4);

    button5 = new JButton("5");
    button5.addActionListener(this);
    buttonPanel.add(button5);

    button6 = new JButton("6");
    button6.addActionListener(this);
    buttonPanel.add(button6);

    buttonMul = new JButton("*");
    buttonMul.addActionListener(this);
    buttonPanel.add(buttonMul);

    button1 = new JButton("1");
    button1.addActionListener(this);
    buttonPanel.add(button1);

    button2 = new JButton("2");
    button2.addActionListener(this);
    buttonPanel.add(button2);

    button3 = new JButton("3");
    button3.addActionListener(this);
    buttonPanel.add(button3);

    buttonSub = new JButton("-");
    buttonSub.addActionListener(this);
    buttonPanel.add(buttonSub);

    button0 = new JButton("0");
    button0.addActionListener(this);
    buttonPanel.add(button0);

    buttonClear = new JButton("C");
    buttonClear.addActionListener(this);
    buttonPanel.add(buttonClear);

    buttonEqual = new JButton("=");
    buttonEqual.addActionListener(this);
    buttonPanel.add(buttonEqual);

    buttonAdd = new JButton("+");
    buttonAdd.addActionListener(this);
    buttonPanel.add(buttonAdd);


    container.add(buttonPanel, BorderLayout.CENTER);

    setSize(280, 210); // 设置窗口尺寸
    setLocation(500, 100); // 设置窗口位置
    setResizable(true); // 禁止窗口大小调整
    setVisible(true); // 显示窗口
}

// 处理按钮的点击事件
@Override
public void actionPerformed(ActionEvent e) {
    String text = e.getActionCommand();
    char ch = text.charAt(0);

    if (ch >= '0' && ch <= '9') { // 数字键
        input.append(ch);
    } else if (text.equals("+") || text.equals("-") || text.equals("*") || text.equals("/")) { // 运算符键
        input.append(" " + ch + " ");
    } else if (text.equals("C")) { // 清除键
        input.setLength(0);
    } else if (text.equals("=")) { // 计算结果
        try {
            String inputStr = input.toString();
            double result = evaluate(inputStr);
            inputField.setText(formatResult(result));
            input.setLength(0);
            input.append(formatResult(result));
        } catch (Exception ex) {
            inputField.setText(ex.getMessage());
            input.setLength(0);
        }
    }

    inputField.setText(input.toString()); // 显示输入
}

// 计算表达式的值（逆波兰表达式算法）
private double evaluate(String inputStr) throws Exception {
    String[] tokens = inputStr.split(" ");
    Stack<Double> stack = new Stack<Double>();
    for (String token : tokens) {
        if (token.isEmpty()) {
            continue;
        }
        char ch = token.charAt(0);
        if (ch >= '0' && ch <= '9') { // 数字
            double num = Double.parseDouble(token);
            stack.push(num);
        } else if (token.length() == 1 && "+-*/".indexOf(ch) >= 0) { // 运算符
            if (stack.size() < 2) {
                throw new Exception("Invalid input");
            }
            double b = stack.pop();
            double a = stack.pop();
            switch (ch) {
                case '+':
                    stack.push(a + b);
                    break;
                case '-':
                    stack.push(a - b);
                    break;
                case '*':
                    stack.push(a * b);
                    break;
                case '/':
                    if (b == 0) {
                        throw new Exception("Division by zero");
                    }
                    stack.push(a / b);
                    break;
            }
        } else {
            throw new Exception("Invalid input");
        }
    }
    if (stack.isEmpty()) {
        throw new Exception("Empty input");
    }
    double result = stack.pop();
    if (!stack.isEmpty()) {
        throw new Exception("Invalid input");
    }
    return result;
}

// 格式化结果字符串
private String formatResult(double result) {
    if (Double.isNaN(result) || Double.isInfinite(result)) {
        return "Error";
    } else if (result == (int) result) {
        return String.format("%d", (int) result);
    } else {
        return String.format("%.2f", result);
    }
}

}