随机更换窗体背景

package table;import java.awt.BorderLayout;import java.awt.EventQueue;import java.awt.Graphics;import java.awt.Image;import java.awt.event.WindowAdapter;import java.awt.event.WindowEvent;import java.util.Random;import javax.swing.JFrame;import javax.swing.JPanel;class MyThread implements Runnable{public void run(){RandomBackgroundImage frame1=new RandomBackgroundImage();frame1.setVisible(true);}}public class RandomBackgroundImage extends JFrame{  private static final long serialVersionUID = -6482396499176910249L;  private JPanel contentPane;  private BackgroundPanel panel;  private Image[] images;    public static void main(String[] args) throws Exception{  MyThread mt=new MyThread();  Thread th=new Thread(mt);  th.start();  Thread.sleep(10); EventQueue.invokeLater(new Runnable(){ public void run(){ try{ RandomBackgroundImage frame=new RandomBackgroundImage(); frame.setVisible(true); }catch(Exception e){ e.printStackTrace(); } } });}  public RandomBackgroundImage(){  initPhotoArray();  addWindowListener(new WindowAdapter(){  public void windowActivated(WindowEvent arg0){  do_this_windowActivated(arg0);  }  });  setTitle("随机更换窗体背景");  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  setBounds(100,100,400,412);//设置位置和大小 contentPane=new JPanel();//创建内容面板  contentPane.setLayout(new BorderLayout(0,0)); setContentPane(contentPane);//设置窗体内容面板  panel=new BackgroundPanel();  contentPane.add(panel);//吧窗体背景面板添加到窗体内容面板  }  private void initPhotoArray(){  images=new Image[4];//初始化背景图数组  String photoPath="";//路径  for(int i=0;i<images.length;i++){//遍历数组并初始化所以元素  photoPath=(i+1)+".jpg";//生成文件名  images[i]=getToolkit().getImage(getClass().getResource(photoPath));//初始化数组  }  }  protected void do_this_windowActivated(WindowEvent arg0){  Random random=new Random();//创建随机数对象  int num=random.nextInt(4);//生成随机数  panel.setImage(images[num]);//设置面板背景图片  repaint();//重绘窗体界面  }}class BackgroundPanel extends JPanel{ private static final long serialVersionUID = 7758689434195492602L; private Image image; public BackgroundPanel(){//构造方法 super(); setOpaque(false); setLayout(null); } public void setImage(Image image){ this.image=image; } protected void paintComponent(Graphics g){//重写绘制组件 if(image!=null){ int width=getWidth(); int height=getHeight(); g.drawImage(image,0,0,width,height,this);//绘制图片与组件大小相同 } super.paintComponent(g); }}