j ava swing简易计算器界面的实现，给出代码

下面是一个简单的Java Swing计算器界面的实现。这个界面只实现了加减乘除四则运算，用户可以通过点击按钮输入数字和运算符，并在结果文本区域中查看计算结果。

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

public class Calculator extends JFrame implements ActionListener{

    private JPanel panel;
    private JTextField textField;
    private JButton button0, button1, button2, button3, button4, button5, button6, button7, button8, button9;
    private JButton buttonAdd, buttonSubtract, buttonMultiply, buttonDivide, buttonClear, buttonEquals;

    private double num1, num2, result;
    private String operator;

    public Calculator(){

        setTitle("Calculator");
        setSize(300, 300);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        panel = new JPanel(new GridLayout(4, 4));
        textField = new JTextField(10);
        textField.setEditable(false);

        button0 = new JButton("0");
        button1 = new JButton("1");
        button2 = new JButton("2");
        button3 = new JButton("3");
        button4 = new JButton("4");
        button5 = new JButton("5");
        button6 = new JButton("6");
        button7 = new JButton("7");
        button8 = new JButton("8");
        button9 = new JButton("9");

        buttonAdd = new JButton("+");
        buttonSubtract = new JButton("-");
        buttonMultiply = new JButton("*");
        buttonDivide = new JButton("/");
        buttonClear = new JButton("C");
        buttonEquals = new JButton("=");

        panel.add(button7);
        panel.add(button8);
        panel.add(button9);
        panel.add(buttonAdd);
        panel.add(button4);
        panel.add(button5);
        panel.add(button6);
        panel.add(buttonSubtract);
        panel.add(button1);
        panel.add(button2);
        panel.add(button3);
        panel.add(buttonMultiply);
        panel.add(buttonClear);
        panel.add(button0);
        panel.add(buttonEquals);
        panel.add(buttonDivide);

        button0.addActionListener(this);
        button1.addActionListener(this);
        button2.addActionListener(this);
        button3.addActionListener(this);
        button4.addActionListener(this);
        button5.addActionListener(this);
        button6.addActionListener(this);
        button7.addActionListener(this);
        button8.addActionListener(this);
        button9.addActionListener(this);
        buttonAdd.addActionListener(this);
        buttonSubtract.addActionListener(this);
        buttonMultiply.addActionListener(this);
        buttonDivide.addActionListener(this);
        buttonClear.addActionListener(this);
        buttonEquals.addActionListener(this);

        add(textField, BorderLayout.NORTH);
        add(panel, BorderLayout.CENTER);
        setVisible(true);

    }

    public void actionPerformed(ActionEvent e){
        if(e.getSource() == button0){
            textField.setText(textField.getText() + "0");
        } else if(e.getSource() == button1){
            textField.setText(textField.getText() + "1");
        } else if(e.getSource() == button2){
            textField.setText(textField.getText() + "2");
        } else if(e.getSource() == button3){
            textField.setText(textField.getText() + "3");
        } else if(e.getSource() == button4){
            textField.setText(textField.getText() + "4");
        } else if(e.getSource() == button5){
            textField.setText(textField.getText() + "5");
        } else if(e.getSource() == button6){
            textField.setText(textField.getText() + "6");
        } else if(e.getSource() == button7){
            textField.setText(textField.getText() + "7");
        } else if(e.getSource() == button8){
            textField.setText(textField.getText() + "8");
        } else if(e.getSource() == button9){
            textField.setText(textField.getText() + "9");
        } else if(e.getSource() == buttonAdd){
            num1 = Double.parseDouble(textField.getText());
            operator = "+";
            textField.setText("");
        } else if(e.getSource() == buttonSubtract){
            num1 = Double.parseDouble(textField.getText());
            operator = "-";
            textField.setText("");
        } else if(e.getSource() == buttonMultiply){
            num1 = Double.parseDouble(textField.getText());
            operator = "*";
            textField.setText("");
        } else if(e.getSource() == buttonDivide){
            num1 = Double.parseDouble(textField.getText());
            operator = "/";
            textField.setText("");
        } else if(e.getSource() == buttonClear){
            textField.setText("");
        } else if(e.getSource() == buttonEquals){
            num2 = Double.parseDouble(textField.getText());
            if(operator.equals("+")){
                result = num1 + num2;
            } else if(operator.equals("-")){
                result = num1 - num2;
            } else if(operator.equals("*")){
                result = num1 * num2;
            } else if(operator.equals("/")){
                result = num1 / num2;
            }
            textField.setText(Double.toString(result));
        }
    }

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