import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class Aj34 extends Applet implements ActionListener
{
Button []buts;
String names[]={"A","B","C","D","E","F","G","H","I","j","k","l"};
boolean toggle=true;
public void init()
{
setLayout(new GridLayout(3,4,5,5));
buts=new Button[names.length];
for(int i=0;i<names.length;i++)
{
buts=new Button("按钮"+names);
buts.addActionListener(this);
add(buts);
}
}
public void actionPerformed(ActionEvent e)
{
if(toggle)
setLayout(new GridLayout(4,3,5,8));
else
setLayout(new GridLayout(3,4,8,5));
toggle=! toggle;
validate();
}
}

为什么按键后就会“三行四列”“四行三列”不同转化？（主要是public void actionPerformed(ActionEvent e)没看懂）

楼主代码有问题，不知道你运行过没有。我修改了下：
package testjui;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class testjui extends Applet implements ActionListener
{
Button buts; //此处修改
String names[]={"A","B","C","D","E","F","G","H","I","j","k","l"};
boolean toggle=true;
public void init()
{
setLayout(new GridLayout(3,4,5,5));
//buts=new Button[names.length];//此处修改
for(int i=0;i<names.length;i++)
{
        buts=new Button("按钮"+names[i]);//此处修改
        buts.addActionListener(this);
        add(buts);
}
}
public void actionPerformed(ActionEvent e)
{
if(toggle)
setLayout(new GridLayout(4,3,5,8));
else
setLayout(new GridLayout(3,4,8,5));
toggle=! toggle;
validate();
}
}

每次执行actionPerformed方法，都会执行toggle=! toggle;这句，在这里实现转化逻辑，然后actionPerformed是在事件

派发的时候调用的，也就是每产生一个点击按钮事件都会被调用，所以无论你点哪个按钮都会有“三行四列”“四行三列

”不同转化。