制作一个简易计算器

import java.awt.*;
import java.awt.event.*;

public class Calculator {
    private Frame frame;
    private Label label;
    private Panel panel;
    private Button button0,button1,button2,button3,button4,button5,button6,button7,button8,
            button9,buttonequ,buttondiv,buttondot,buttonmul,buttonsub,buttonadd;
    private ButtonHandler listener;

    public Calculator() {
        frame = new Frame("My Calculator");
        label = new Label("0", Label.RIGHT);
        panel = new Panel(new GridLayout(4, 4));
        button0 = new Button("0");
        button1 = new Button("1");
        button2 = new Button("2");
        button3 = new Button("3");
        button4 = new Button("4");
        button5 = new Button("5");
        button6 = new Button("6");
        button7 = new Button("7");
        button8 = new Button("8");
        button9 = new Button("9");
        buttonequ = new Button("=");
        buttondiv = new Button("/");
        buttondot = new Button(".");
        buttonmul = new Button("*");
        buttonsub = new Button("-");
        buttonadd = new Button("+");
        panel.add(button7);
        panel.add(button8);
        panel.add(button9);
        panel.add(buttonadd);
        panel.add(button4);
        panel.add(button5);
        panel.add(button6);
        panel.add(buttonsub);
        panel.add(button1);
        panel.add(button2);
        panel.add(button3);
        panel.add(buttonmul);
        panel.add(button0);
        panel.add(buttondot);
        panel.add(buttonequ);
        panel.add(buttondiv);
        frame.add(label, BorderLayout.NORTH);
        frame.add(panel, BorderLayout.CENTER);
        frame.pack();
        frame.setSize(300,300);
        frame.setVisible(true);

        listener = new ButtonHandler();

        //对按钮添加监听
        button0.addActionListener(listener);
        button1.addActionListener(listener);
        button2.addActionListener(listener);
        button3.addActionListener(listener);
        button4.addActionListener(listener);
        button5.addActionListener(listener);
        button6.addActionListener(listener);
        button7.addActionListener(listener);
        button8.addActionListener(listener);
        button9.addActionListener(listener);
        buttonadd.addActionListener(listener);
        buttonsub.addActionListener(listener);
        buttonmul.addActionListener(listener);
        buttondiv.addActionListener(listener);
        buttondot.addActionListener(listener);
        buttonequ.addActionListener(listener);

        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
    }

    class ButtonHandler implements ActionListener {
        int flag = 0; //存储运算符
        boolean equHappened = true;
        double arg1 = 0, arg2 = 0, result = 0;
        //@Override
        public void actionPerformed(ActionEvent e) {
            if(e.getSource() == buttonequ) {
                equHappened = true;
                if(flag==0) {
                    result = arg1 + arg2;
                }
                else if(flag==1) {
                    result = arg1 - arg2;
                }
                else if(flag==2) {
                    result = arg1 * arg2;
                }
                else {
                    result = arg1 / arg2;
                }
                label.setText(result+"");
            }
            else {
                if(equHappened == true) {
                    label.setText("");
                    equHappened = false;
                }

                if(e.getSource() == buttondot) {
                    label.setText("0.");
                }
                else if(e.getSource() == button0) {
                    label.setText(label.getText()+"0");
                    arg2 = Double.parseDouble(label.getText());
                }
                else if(e.getSource() == button1) {
                    label.setText(label.getText()+"1");
                    arg2 = Double.parseDouble(label.getText());
                }
                else if(e.getSource() == button2) {
                    label.setText(label.getText()+"2");
                    arg2 = Double.parseDouble(label.getText());
                }
                else if(e.getSource() == button3) {
                    label.setText(label.getText()+"3");
                    arg2 = Double.parseDouble(label.getText());
                }
                else if(e.getSource() == button4) {
                    label.setText(label.getText()+"4");
                    arg2 = Double.parseDouble(label.getText());
                }
                else if(e.getSource() == button5) {
                    label.setText(label.getText()+"5");
                    arg2 = Double.parseDouble(label.getText());
                }
                else if(e.getSource() == button6) {
                    label.setText(label.getText()+"6");
                    arg2 = Double.parseDouble(label.getText());
                }
                else if(e.getSource() == button7) {
                    label.setText(label.getText()+"7");
                    arg2 = Double.parseDouble(label.getText());
                }
                else if(e.getSource() == button8) {
                    label.setText(label.getText()+"8");
                    arg2 = Double.parseDouble(label.getText());
                }
                else if(e.getSource() == button9) {
                    label.setText(label.getText()+"9");
                    arg2 = Double.parseDouble(label.getText());
                }
                else if(e.getSource() == buttonadd) {
                    label.setText("");
                    arg1 = arg2;
                    flag = 0;
                }
                else if(e.getSource() == buttonsub) {
                    label.setText("");
                    arg1 = arg2;
                    flag = 1;
                }
                else if(e.getSource() == buttonmul) {
                    label.setText("");
                    arg1 = arg2;
                    flag = 2;
                }
                else if(e.getSource() == buttondiv) {
                    label.setText("");
                    arg1 = arg2;
                    flag = 3;
                }
            }
        }
    }

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