Question

The question I have is exactly same in requirement as How to pass mouse events to applications behind mine in C#/Vista? , but I need the same for a Transparent Java UI. I can easily create a transparent Java UI using 6.0 but couldn’t get any info about passing events through the app to any applications(say a browser) behind.

Answer 1

I believe this will answer your question. To run it you will need Java 6 update 10 and above.
I tested it on Windows Vista

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class ClickThrough {

    public static void main(String[] args) {
        JFrame.setDefaultLookAndFeelDecorated(true);
        JFrame f = new JFrame("Test");
        f.setAlwaysOnTop(true);
        Component c = new JPanel() {
            @Override
            public void paintComponent(Graphics g) {
                Graphics2D g2 = (Graphics2D)g.create();
                g2.setColor(Color.gray);
                int w = getWidth();
                int h = getHeight();
                g2.fillRect(0, 0, w,h);
                g2.setComposite(AlphaComposite.Clear);
                g2.fillRect(w/4, h/4, w-2*(w/4), h-2*(h/4));
            }
        };
        c.setPreferredSize(new Dimension(300, 300));
        f.getContentPane().add(c);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.pack();
        f.setVisible(true);
        com.sun.awt.AWTUtilities.setWindowOpaque(f,false);
    }

}

Note that you need to either have an undecorated window or one that is decorated by Java alone (not the default OS decoration) otherwise the code won’t work.