import java.awt.*;import java.awt.event.*;
import javax.swing.*;
/**
* MainForm.java Created by karin at 2012-9-11
*/

public class MainForm extends JFrame implements ActionListener {
public static void main(String[] args) { // TODO Auto-generated method stub
int count = 0;
MainForm mainFrame = new MainForm();
mainFrame.setTitle(主窗体);

mainFrame.setBounds(new Rectangle(200, 200, 500, 500));
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container c = mainFrame.getContentPane();
c.setLayout(new BorderLayout()); // 进行顺序排放组件的设置
c.setLayout(null);
JButton btn = new JButton(更改大小);

btn.addActionListener(mainFrame);
btn.setBounds(50, 50, 100, 100);
btn.setVisible(true);
c.add(btn);

mainFrame.setVisible(true); }
public void actionPerformed(ActionEvent e) {
this.setBounds(new Rectangle(200, 200, 300, 300));
}

} 说具体一点儿。是网页吗？ 添加一个 resize()试试看。 hover事件，点击事件改变图片 JFrame.setSize 方法 import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
class Jframe extends JFrame {
public Jframe() {
add();
button();
}

public void add() {
this.setSize(300, 200);
this.setLocationRelativeTo(null);
this.setLayout(null);
this.setVisible(true);
}
public void button() {
JButton j = new JButton(点击);
j.setBounds(99, 66, 60, 30);
j.addActionListener(new ActionListener() {

@Override
public void actionPerformed(ActionEvent arg0) {
Jframe.this.setSize(500, 400);
Jframe.this.repaint();
}
});
this.add(j);
}

public static void main(String[] args) {
new Jframe();
}
}