有关GUI的一个有关问题

import java.awt.FlowLayout;import javax.swing.JButton;import javax.swing.JFrame;public class Test111{    public static void main(String[] args) {        JFrame jf = new JFrame();        for(int i=0;i<100;i++){            JButton jb = new JButton("helloworld!");            jf.add(jb);        }        jf.setLayout(new FlowLayout(0));        jf.setSize(400, 300);        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        jf.setVisible(true);    }}

 
 package test.org.ross.util; 
 import java.awt.*; 
 import java.awt.event.*; 
 import javax.swing.*; 
 public class CardLayoutDemo implements ActionListener{ 
 JPanel p1,p2,p3,p4; 
 int i=1; 
 JFrame f; 
 public CardLayoutDemo(){ 
   f=new JFrame();//当做top-level组件 
   Container contentPane=f.getContentPane(); 
   contentPane.setLayout(new GridLayout(2,1)); 
    
   p1=new JPanel(); 
   Button b=new Button("Change Card"); 
   b.addActionListener(this);//当按下"Change Card"时，进行事件监听，将会有系统操作产生。 
   p1.add(b);        //处理操作在52-64行. 
   contentPane.add(p1); 
    
   p2=new JPanel(); 
   p2.setLayout(new FlowLayout()); 
   p2.add(new JButton("first")); 
   p2.add(new JButton("second")); 
   p2.add(new JButton("third")); 
    
   p3=new JPanel(); 
   p3.setLayout(new GridLayout(100,1)); 
   for (int i = 0; i  < 100; i++) { 
   	  p3.add(new JButton(""+i)); 
   } 
    
   p4=new JPanel(); 
   p4.setLayout(new CardLayout()); 
   p4.add("one",p2); 
   p4.add("two",new JScrollPane(p3)); 
   /*要显示CardLayout的卡片，除了用show(Container parent,String name)这个方法外 
    *，也可试试first(Container),next(Container),previous(Container),last(Container)这 
    *四个方法，一样可以达到显示效果。 
    */ 
   ((CardLayout)p4.getLayout()).show(p4,"one"); 
    
   contentPane.add(p4); 
    
   f.setTitle("CardLayout"); 
   f.pack(); 
   f.setVisible(true); 
    
   f.addWindowListener( 
      new WindowAdapter(){ 
        public void windowClosing(WindowEvent e){ 
         System.exit(0);	 
        }	 
      }	 
   ); 
    
 } 
 public void actionPerformed(ActionEvent event){ 
    switch(i){ 
     case 1: 
        ((CardLayout)p4.getLayout()).show(p4,"two"); 
        break; 
     case 2: 
        ((CardLayout)p4.getLayout()).show(p4,"one"); 
        break; 
    } 
    i++; 
    if (i==3) i=1; 
    f.validate(); 
 } 
 public static void main(String[] args){ 
 	 new CardLayoutDemo(); 
 } 
 }