How to change default operating system's frame around swing application

Question

For example instead of the default operating system container around the application you could have something custom like this swing project below.

Answer 1

You can use a transparent image on a undecorated frame with a transparent background:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class TransparentImageFrame
{
    private static void createAndShowUI()
    {
        JLabel label = new JLabel( new ImageIcon("...") );
        label.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e)
            {
                if (e.getClickCount() == 2)
                {
                    System.exit(0);
                }
            }
        });

        JFrame frame = new JFrame("Image Frame");
        frame.setUndecorated(true);
        frame.setBackground(new Color(0, 0, 0, 0));

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());
        frame.add( label );
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowUI();
            }
        });
    }
}

The mouse will only respond to non-opaque pixels in whatever image you use.

Answer 2

The host OS owns the frame decorations, but you can Create Translucent and Shaped Windows and use Frame#setUndecorated(), as shown here.