AlphaComposite doesnt work as expected

Question

From the tutorial [http://download.oracle.com/javase/tutorial/2d/advanced/compositing.html]
Source-in (SRC_IN): If pixels in the source and the destination overlap, only the source pixels in the overlapping area are rendered.
Output from the code below is different from the description.
import javax.swing.*;
import java.awt.*;
import java.awt.image.*;
import java.awt.geom.*;
public class Main
{   public static void main(String[] args)
    {   SwingUtilities.invokeLater(new Runnable()
        {   public void run()
            {   createAndShowGUI();
    private static void createAndShowGUI()
    {   JFrame f = new JFrame("My GUI");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        CompositionGUI GUI = new CompositionGUI();
        f.setContentPane(GUI);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(1200, 300);
        f.setVisible(true);
class CompositionGUI extends JPanel
{   public CompositionGUI(){}
    private int getRule(int rule)
    {   switch( rule )
        {   case 0: return AlphaComposite.CLEAR;
            case 1: return AlphaComposite.DST;
            case 2: return AlphaComposite.DST_ATOP;
            case 3: return AlphaComposite.DST_IN;
            case 4: return AlphaComposite.DST_OUT;
            case 5: return AlphaComposite.DST_OVER;
            case 6: return AlphaComposite.SRC;
            case 7: return AlphaComposite.SRC_ATOP;
            case 8: return AlphaComposite.SRC_IN;
            case 9: return AlphaComposite.SRC_OUT;
            case 10: return AlphaComposite.SRC_OVER;
            case 11: return AlphaComposite.XOR;
            default: return AlphaComposite.SRC;
    private String getRuleName(int i)
    {   switch(i)
        {   case 0: return "CLEAR";
            case 1: return "DST";
            case 2: return "DST_ATOP";
            case 3: return "DST_IN";
            case 4: return "DST_OUT";
            case 5: return "DST_OVER";
            case 6: return "SRC";
            case 7: return "SRC_ATOP";
            case 8: return "SRC_IN";
            case 9: return "SRC_OUT";
            case 10: return "SRC_OVER";
            case 11: return "XOR";
            default: return "Unknow";
    public void paintComponent(Graphics g)
    {   super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        BufferedImage buffImg = new BufferedImage(100, 100, BufferedImage.TYPE_INT_ARGB);
        Graphics2D gbi = buffImg.createGraphics();
        g2.setColor(Color.ORANGE);
        Composite def = gbi.getComposite();
        for(int i=0;i<3;i++)
            for(int j=0;j<12;j++)
            {   gbi.setColor(new Color(0.0f, 0.0f, 1.0f, 1.0f));
                gbi.setComposite(def);
                gbi.fill(new Rectangle2D.Double(0, 0, 50, 50));
                gbi.setColor(new Color(1.0f, 0.0f, 0.0f, 1.0f));
                gbi.setComposite(AlphaComposite.getInstance(getRule(j),i*0.5f));
                gbi.fill(new Ellipse2D.Double(25, 25, 50, 50));
                g2.drawImage(buffImg, null, j*100, i*100);
                g2.drawString(getRuleName(j), 10+j*100, i*100+20);
}

Answer 1

This might work:
@Override public void paintComponent(Graphics g) {
  super.paintComponent(g);
  Graphics2D g2 = (Graphics2D)g;
  for(int i=0; i<3; i++) {
    for(int j=0; j<12; j++) {
      BufferedImage buffImg = new BufferedImage(100,100,BufferedImage.TYPE_INT_ARGB);
      Graphics2D gbi = buffImg.createGraphics();
      Composite def = gbi.getComposite();
      gbi.setColor(new Color(0.0f, 0.0f, 1.0f, 1.0f));
      gbi.setComposite(def);
      gbi.fill(new Rectangle2D.Double(0, 0, 50, 50));
      gbi.setColor(new Color(1.0f, 0.0f, 0.0f, 1.0f));
      gbi.setComposite(AlphaComposite.getInstance(getRule(j),i*0.5f));
      gbi.fill(new Ellipse2D.Double(25, 25, 50, 50));
      gbi.dispose();
      g2.drawImage(buffImg, null, j*100, i*100);
      g2.setColor(Color.ORANGE);
      g2.drawString(getRuleName(j), 10+j*100, i*100+20);
}