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

public class Calculator extends JFrame implements ActionListener {
    private JTextField display;
    private double num1 = 0, num2 = 0, result = 0;
    private String operation = "";

    public Calculator() {
        setTitle("简易计算器");
        setSize(400, 600);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());

        // 显示屏
        display = new JTextField();
        display.setEditable(false);
        display.setHorizontalAlignment(JTextField.RIGHT);
        add(display, BorderLayout.NORTH);

        // 按钮面板
        JPanel panel = new JPanel();
        panel.setLayout(new GridLayout(4, 4, 10, 10));
        String[] buttons = {"7", "8", "9", "/", "4", "5", "6", "*", "1", "2", "3", "-", "C", "0", "=", "+"};
        for (String text : buttons) {
            JButton button = new JButton(text);
            button.addActionListener(this);
            panel.add(button);
        }
        add(panel, BorderLayout.CENTER);

        setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();
        if (command.equals("C")) {
            clearDisplay();
        } else if (command.equals("=")) {
            calculateResult();
        } else {
            handleInput(command);
        }
    }

    private void handleInput(String input) {
        if (input.matches("[0-9]")) {
            display.setText(display.getText() + input);
        } else {
            operation = input;
            num1 = Double.parseDouble(display.getText());
            display.setText("");
        }
    }

    private void calculateResult() {
        num2 = Double.parseDouble(display.getText());
        switch (operation) {
            case "+":
                result = num1 + num2;
                break;
            case "-":
                result = num1 - num2;
                break;
            case "*":
                result = num1 * num2;
                break;
            case "/":
                if (num2 != 0) {
                    result = num1 / num2;
                } else {
                    display.setText("Error");
                    return;
                }
                break;
            case "%":
                result = num1 % num2;
                break;
        }
        display.setText(String.valueOf(result));
    }

    private void clearDisplay() {
        display.setText("");
        num1 = 0;
        num2 = 0;
        result = 0;
        operation = "";
    }

    public static void main(String[] args) {
        new Calculator();
    }
}