java 简易计算器增加历史记录功能

以下是一个简易计算器增加历史记录功能的Java代码示例：

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

public class CalculatorWithHistory extends JFrame {
    private JTextField result_Jtf;
    private JButton CE;
    private JButton history;
    private JButton equal;
    private String str = "";
    private String[] historyArr = new String[5];
    private int countEqu = 0;

    public CalculatorWithHistory() {
        setTitle("Calculator");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());

        result_Jtf = new JTextField();
        result_Jtf.setEditable(false);
        add(result_Jtf, BorderLayout.NORTH);

        JPanel panel3 = new JPanel();
        panel3.setLayout(new GridLayout(1, 2));

        CE = new JButton("CE");
        CE.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                str = "";                result_Jtf.setText(str);
            }
        });

        history = new JButton("历史记录");
        history.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                StringBuilder historyStr = new StringBuilder();
                for (int i = 0; i < historyArr.length; i++) {
                    if (historyArr[i] != null) {
                        historyStr.append(historyArr[i]).append("\n");
                    }
                }
                JOptionPane.showMessageDialog(null, historyStr.toString(), "历史记录", JOptionPane.INFORMATION_MESSAGE);
            }
        });

        panel3.add(CE);
        panel3.add(history);
        add(panel3, BorderLayout.SOUTH);

        JPanel panel1 = new JPanel();
        panel1.setLayout(new GridLayout(4, 4));

        String[] buttonLabels = {"7", "8", "9", "/",
                "4", "5", "6", "*",
                "1", "2", "3", "-",
                "0", ".", "=", "+"};

        for (String label : buttonLabels) {
            JButton button = new JButton(label);
            button.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    String actionBut = e.getActionCommand();
                    str = str + actionBut;
                    result_Jtf.setText(str);
                }
            });
            panel1.add(button);
        }

        add(panel1, BorderLayout.CENTER);

        equal = new JButton("=");
        equal.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                str = calculate(str);
                result_Jtf.setText(str);
                countEqu = countEqu % 5;
                historyArr[countEqu] = str;
                countEqu++;
                str = "";
            }
        });
        add(equal, BorderLayout.EAST);

        pack();
        setVisible(true);
    }

    private String calculate(String expression) {
        // 实现表达式求值的逻辑
        // ...
        return result;
    }

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