图片组成2D动画

import java.awt.AlphaComposite;   
import java.awt.Graphics;   
import java.awt.Graphics2D;   
import java.awt.Image;   
import java.awt.event.ActionEvent;   
import java.awt.event.ActionListener;   
import java.awt.image.BufferedImage;   
  
import javax.swing.ImageIcon;   
import javax.swing.JFrame;   
import javax.swing.JPanel;   
import javax.swing.Timer;   
  
public class ImageComposite extends JPanel implements ActionListener {   
  Image a = new ImageIcon(this.getClass().getResource("a.png")).getImage();   
  Image b = new ImageIcon(this.getClass().getResource("b.png")).getImage();   
  Timer timer = new Timer(800, this);   
  float alpha = 1f;   
  
  public ImageComposite() {   
    timer.start();   
  }   
  
  public void paint(Graphics g) {   
    super.paint(g);   
    Graphics2D g2d = (Graphics2D) g;   
  
    BufferedImage buffImg = new BufferedImage(200, 100, BufferedImage.TYPE_INT_ARGB);   
    Graphics2D gbi = buffImg.createGraphics();   
  
    AlphaComposite ac = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha);   
  
    gbi.drawImage(a, 40, 30, null);   
    gbi.setComposite(ac);   
    gbi.drawImage(b, 0, 0, null);   
  
    g2d.drawImage(buffImg, 20, 20, null);   
  }   
  public void actionPerformed(ActionEvent e) {   
    alpha -= 0.1;   
    if (alpha <= 0) {   
      alpha = 0;   
      timer.stop();   
    }   
    repaint();   
  }   
  
  public static void main(String[] args) {   
    JFrame frame = new JFrame();   
    frame.add(new ImageComposite());   
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);   
    frame.setSize(300, 210);   
    frame.setVisible(true);   
  }   
  
}