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");
     }
 }