简易计算器。比如：按键得到23*2.2，单击“=”得出结果50.6。“MC”键实现清除右侧的显示内容。界面如下图所示。

很抱歉，我之前的回答有些错误。以下是一个简单的Java Eclipse计算器的源代码，仅供参考：

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

public class Calculator extends JFrame {
    private static final long serialVersionUID = 1L;
    //创建文本框
    JTextField text = new JTextField("0");
    //定义计算器需要的变量
    double number1 = 0.0;
    double number2 = 0.0;
    double result = 0.0;
    String operator = "";
    boolean isFirstDigit = true;

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

    public Calculator() {
        super();
        //设置窗口属性
        setTitle("简易计算器");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(250, 300);
        setLocation(500, 200);
        //设置面板布局
        JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());
        //将文本框添加到面板中
        panel.add(text, BorderLayout.NORTH);
        //创建按钮
        JButton btn0 = new JButton("0");
        JButton btn1 = new JButton("1");
        JButton btn2 = new JButton("2");
        JButton btn3 = new JButton("3");
        JButton btn4 = new JButton("4");
        JButton btn5 = new JButton("5");
        JButton btn6 = new JButton("6");
        JButton btn7 = new JButton("7");
        JButton btn8 = new JButton("8");
        JButton btn9 = new JButton("9");
        JButton btnAdd = new JButton("+");
        JButton btnSub = new JButton("-");
        JButton btnMul = new JButton("*");
        JButton btnDiv = new JButton("/");
        JButton btnEq = new JButton("=");
        JButton btnClear = new JButton("MC");
        //创建一个监听器
        ActionListener listener = new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String command = e.getActionCommand();
                if (isFirstDigit) {
                    text.setText("");
                    isFirstDigit = false;
                }
                text.setText(text.getText() + command);
            }
        };
        //给数字按钮添加监听器
        btn0.addActionListener(listener);
        btn1.addActionListener(listener);
        btn2.addActionListener(listener);
        btn3.addActionListener(listener);
        btn4.addActionListener(listener);
        btn5.addActionListener(listener);
        btn6.addActionListener(listener);
        btn7.addActionListener(listener);
        btn8.addActionListener(listener);
        btn9.addActionListener(listener);
        //给操作符按钮添加监听器
        ActionListener operatorListener = new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                operator = e.getActionCommand();
                number1 = Double.parseDouble(text.getText());
                isFirstDigit = true;
            }
        };
        btnAdd.addActionListener(operatorListener);
        btnSub.addActionListener(operatorListener);
        btnMul.addActionListener(operatorListener);
        btnDiv.addActionListener(operatorListener);
        //给“=”按钮添加监听器
        btnEq.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                number2 = Double.parseDouble(text.getText());
                switch (operator) {
                case "+":
                    result = number1 + number2;
                    break;
                case "-":
                    result = number1 - number2;
                    break;
                case "*":
                    result = number1 * number2;
                    break;
                case "/":
                    result = number1 / number2;
                    break;
                }
                text.setText(String.valueOf(result));
                isFirstDigit = true;
            }
        });
        //给“MC”按钮添加监听器
        btnClear.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                text.setText("0");
                isFirstDigit = true;
            }
        });
        //创建面板，将按钮添加到面板中
        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new GridLayout(4, 4));
        buttonPanel.add(btn7);
        buttonPanel.add(btn8);
        buttonPanel.add(btn9);
        buttonPanel.add(btnDiv);
        buttonPanel.add(btn4);
        buttonPanel.add(btn5);
        buttonPanel.add(btn6);
        buttonPanel.add(btnMul);
        buttonPanel.add(btn1);
        buttonPanel.add(btn2);
        buttonPanel.add(btn3);
        buttonPanel.add(btnSub);
        buttonPanel.add(btn0);
        buttonPanel.add(btnClear);
        buttonPanel.add(btnEq);
        buttonPanel.add(btnAdd);
        //将面板添加到主面板中
        panel.add(buttonPanel, BorderLayout.CENTER);
        //将主面板添加到窗口中
        this.setContentPane(panel);
    }
}

希望这个源代码对你有所帮助。