SystemTrayMinimal.java

/*
 * Copyright Benjamin Howe 2018
 * This code is released under the CC0 license
 * See: https://creativecommons.org/publicdomain/zero/1.0/
 */
package uk.bh96;

import java.awt.AWTException;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.SystemTray;
import java.awt.TrayIcon;
import java.awt.image.BufferedImage;
import java.io.IOException;

public class SystemTrayMinimal {

    public static void main(String[] args) throws AWTException, IOException {
        // create the graphic for the tray icon
        BufferedImage trayIconImage = new BufferedImage(256, 256, BufferedImage.TYPE_INT_ARGB);
        Graphics2D graphic = trayIconImage.createGraphics();
        graphic.setBackground(Color.RED);
        graphic.clearRect(0, 0, 256, 256);
        
        // resize the tray icon
        SystemTray tray = SystemTray.getSystemTray();
        int trayIconWidth = tray.getTrayIconSize().width;
        TrayIcon trayIcon = new TrayIcon(trayIconImage.getScaledInstance(trayIconWidth, -1, Image.SCALE_SMOOTH));
        System.out.println("The tray icon was resized to " + trayIconWidth + "px wide.");
        
        // add the tray icon to the tray
        tray.add(trayIcon);
        
        // wait for input, then die
        System.in.read();
        System.exit(0);
    }
    
}

See: https://www.raspberrypi.org/forums/viewtopic.php?f=81&t=209142