JAVA的继承，构造函数，窗体

import java.awt.*;
import javax.swing.*;
import javax.swing.JFrame;
import java.awt.event.WindowListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
class QQ extends JFrame   //继承JFrame
{
    QQ()  //构造函数
    {
        display();//调用display()函数
    }
    JButton btn1;
    JButton btn2;
    JTextField jtf1;
    JPasswordField jpf1; //密码文本
    class MyListener extends WindowAdapter //适配器   是扩展  不需要覆盖WindowAdapter中的所有方法 功能代码较多
    {
        public void windowClosing(WindowEvent e)
        {
            System.out.println("windowClosing");
            int res = JOptionPane.showConfirmDialog(null,"是否退出程序应用","提示", JOptionPane.YES_NO_OPTION); //弹出消息框
            System.out.println("res =" + res);
            if(res == 0)
            {
                System.out.println("退出");
                System.exit(1);// 退出
                System.out.println("退出1"); //不输出  因为exit先执行
            }
            else if(res == 1)
            {
                System.out.println("不退出");
                setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
                //System.exit(1);// 退出
                // 不退出
            }
        }
    }
    class BtnAction implements ActionListener  //btn事件
    {
        public void actionPerformed(ActionEvent e)
        {
            System.out.println("actionPerformed");
            if(jtf1.getText().equals("jk") && jpf1.getText().equals("jk"))
            {
                System.out.println("OK");
                dispose();
                (new JFrame("主窗口")).setVisible(true);
            }
            else
            {
                System.out.println("Error");
                JOptionPane.showConfirmDialog(null,"密码错误","提示", JOptionPane.DEFAULT_OPTION);
            }
        }
    }
    class BtnAction2 implements ActionListener   //内部类
    {
        public void actionPerformed(ActionEvent e)
        {
            Object o = e.getSource();
            JButton b = (JButton)o;  //强制类型转换
            System.out.println("芝麻开门" + btn2.getText());  //类的成员/函数，可以在内部类中使用
            
            if(b == btn2) //b.getSource == "注册"
            {
                jtf1.setText("");
                jpf1.setText("");
            }
        }
    }
    public void display()
    {
        //JFrame frm = new JFrame(); //窗体
        ImageIcon img1 = new ImageIcon("timg.gif"); //背景
        JLabel background1 = new JLabel(img1);
        this.getLayeredPane().add(background1, new Integer(Integer.MIN_VALUE)); 
        //background.setBounds(0, 0, img.getIconWidth(), img.getIconHeight());
        background1.setBounds(0, 0, 425, 450);
        ImageIcon img2 = new ImageIcon("33.gif"); 
        JLabel background2 = new JLabel(img2);
        this.getLayeredPane().add(background2, new Integer(Integer.MIN_VALUE)); 
        background2.setBounds(0, 0, img2.getIconWidth(), img2.getIconHeight());
        
        jtf1 = new JTextField(30); //文本
        //jtf1.setColumns(10);
        jtf1.setSize(200,35);
        jtf1.setLocation(130,130);
        jpf1 = new JPasswordField(30); //密码文本
        //jpf1.setEchoChar('#');     设置密码文本内容
        jpf1.setSize(200,35);
        jpf1.setLocation(130,180);
        
        JLabel lab1 = new JLabel("账号："); //标题
        Font fnt = new Font("Serief",Font.ITALIC+Font.BOLD,15);
        lab1.setFont(fnt);
        lab1.setBackground(Color.BLUE); //label的背景颜色
        lab1.setOpaque(true); //label是否透明
        lab1.setForeground(Color.YELLOW); //label前景色
        JLabel lab2 = new JLabel("密码：");
        lab1.setSize(50,30);
        lab2.setSize(50,30);
        lab1.setLocation(70,130);
        lab2.setLocation(70,180);
        btn1 = new JButton("登录");
        btn1.setBounds(100,230,180,50);
        Image im1 = (new ImageIcon("QQ.png")).getImage(); //图标
        this.setIconImage(im1);
        //ImageIcon im2 = new ImageIcon("77.png"); //图标
        ImageIcon im2 = new ImageIcon("./77.png");
        btn1.setIcon(im2);
        this.setLayout(null);  //布局--绝对布局
        MyListener ltn = new MyListener();  //监听
        this.addWindowListener(ltn);
        BtnAction act = new BtnAction();    //btn事件
        btn1.addActionListener(act);
        btn2 = new JButton("重置");
        btn2.setBounds(300,230,100,50);
        BtnAction2 act2 = new BtnAction2();
        btn2.addActionListener(act2);
        //frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(425,325);
        this.setLocation(700,500);
        this.setTitle("QQ登录");
        this.setResizable(false);        
        this.add(btn1);
        this.add(btn2);
        this.add(lab1);
        this.add(lab2);
        this.add(jpf1);
        this.add(jtf1);
        this.add(background1);
        this.add(background2);
        this.setVisible(true);
        System.out.println("OK");
    }
    public static void main(String[] args)
    {
        QQ Event1 = new QQ();
        System.out.println("OK");
    }
}