java fullscreen window with transparency

I am trying to create a fullscreen window that cover the whole screen using Java. This window must also have some transparency (about 30%-50% transparent). When saying whole screen, I do mean it cover everything (including the dock/taskbar/menubar in OSX/Linux/Windows), and when I say with transparancy, I mean a real-time transparancy and not just a hacked screenshot. Here is what I am aware-of/tried:

Using Java Fullscreen API: while it creates a true fullscreen, you cannot have some transparency with it (only opaque color). One hack is to take a screenshot of the whole desktop and set it as background for the window, but this mean it is not real-time transparency.
Setting window size to match screen dimension: while it fills the whole screen, in certain OSes (e.g. Mac OS X) the window will be rendered behind the dock/menubar, and not above it. However, transparency do work here.
Using setWindowOpacity API: it work in the second case, but not in the first (Fullscreen API)
Using setBackground with alpha: it work like the setWindowOpacity, but only in certain OSes. But also doesn't work with Fullscreen API.
Use JFrame/JWindow/JDialog/Frame/Window: tried every window model I could, without any luck

So I am asking if this is possible through a another hack that I am not aware of, then I would be happy to hear about.

The goal is to overlay a semi-transparent fullscreen over the desktop.

is possible only with visible TaskBar e.i.

GraphicsEnvironment.getLocalGraphicsEnvironment().getMaximumWindowBounds();

otherwise you got and exception

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: 
The effects for full-screen windows are not supported.

or by using brutte_force to DirectX freezed my PC twicw, only power_off to save PC's GPU

import com.sun.awt.AWTUtilities;
import java.awt.Dimension;
import java.awt.GraphicsEnvironment;
import java.awt.Rectangle;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class JFrameOpacityExample {

    private JFrame myFrame = new JFrame("Test Frame");
    private boolean opacity = true;
    private boolean resize = true;
    private JButton button = new JButton("Opacity");
    private JButton button1 = new JButton("Resize");

    public JFrameOpacityExample() {
        button.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent evt) {
                Object src = evt.getSource();
                if (opacity) {
                    AWTUtilities.setWindowOpacity(myFrame, 0.50f);
                    opacity = false;
                } else {
                    AWTUtilities.setWindowOpacity(myFrame, 1.0f);
                    opacity = true;
                }
            }
        });
        button1.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent evt) {
                Object src = evt.getSource();
                if (resize) {
                    Rectangle dim = GraphicsEnvironment.getLocalGraphicsEnvironment().getMaximumWindowBounds();
                    int h = dim.height;
                    int w = dim.width;
                    myFrame.setBounds(00, 00, w, h);
                    resize = false;
                } else {
                    myFrame.setBounds(100, 100, 400, 400);
                    resize = true;
                }
            }
        });
        JPanel panel = new JPanel();
        panel.add(button);
        panel.add(button1);
        myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        myFrame.add(panel);
        myFrame.setSize(400, 400);
        myFrame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {

            public void run() {
                JFrameOpacityExample jFrameOpacityExample = new JFrameOpacityExample();
            }
        });
    }
}