java自学者编写的计算器代码

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

public class ComponentEvent2 extends Frame implements ActionListener , WindowListener
{   
float x,y,z;
Button b1 = new Button("+");
    Button b2 = new Button("-");
Button b3 = new Button("*");
Button b4 = new Button("/");
Button b5 = new Button("退出");
    TextField tf1 = new TextField("",8); 
    TextField tf2 = new TextField("",8);
    TextField tf3 = new TextField("",20);
    public ComponentEvent2()
{
super("我的计算器");
        b1.addActionListener(this);
        b2.addActionListener(this);
        b3.addActionListener(this);
        b4.addActionListener(this);
        b5.addActionListener(this);
setLayout( new FlowLayout() );
add(tf1);add(tf2);

        add(b1);add(b2);add(b3); add(b4);

        addWindowListener(this);
add(tf3);
add(b5);