Minimizing java GUI to sys tray

Question

I want to write an alarm scheduler GUI which will continuously run on the system, both Windows and Mac. Here are the tasks I need to accomplish:
1) When the user clicks on the close window or "X" sign, I simply want to minimize the gui to sys tray in case of Windows, or push it to background in case of Mac (somehow hide the GUI from the screen in both cases).
2) Another requirement is that if the user starts the program from desktop by clicking on an icon, the program should check to see if an instance of itself is already running, and if so, load the running instance. And what i mean by that is to bring the GUI back to screen. If the program is not already running, start a brand new instance of it.
Any help would be much appreciated.

Answer 1

Prometheus, appreciate the help. But using singleton pattern doesnt solve the problem. Here is my code for singleton and the test classes.
package com.vetinsite.scheduler;
public class Singleton {
    private static com.vetinsite.scheduler.Singleton uniqueInstance;
    private int var;
    private Singleton() {}
    public static synchronized Singleton getInstance(){
        if(uniqueInstance == null){
             uniqueInstance = new Singleton();
        return uniqueInstance;
    public void setVar(int v){
        this.var = v;
    public void print(){
        System.out.println(var);
package com.vetinsite.scheduler;
public class Test1 {
    public static void main (String argv[]){
        com.vetinsite.scheduler.Singleton single = Singleton.getInstance();
        single.setVar(1);
        single.print();
        single.setVar(2);
        try{
             Thread.sleep(10000);
        catch (Exception e){}
        single = Singleton.getInstance();
        single.print();
package com.vetinsite.scheduler;
public class Test2 {
    public static void main (String argv[]){
        com.vetinsite.scheduler.Singleton single = Singleton.getInstance();
        single.print();
}I run Test1 which sets the singleton's "var" variable to 1 and then 2. Then sleeps for 10 second. Within the 10 sec period I run Test2 expecting it to print out "2", but it instead prints "0". I guess my understanding of singleton pattern is wrong, becoz I thought if two different classes in the same package tried to instantiate the singleton object, it would one create one instance. But in this test its obviously creating two.
If I cant use singleton pattern, is there any other means by which I can reload the running instance of a GUI.