The following code will display the current position of the application window when you click on it. Try dragging the window to different positions and clicking on it.

The variable frame is the JFrame used for the application window but the method getLocationOnScreen() will work for any JFrame provided it is being displayed. That is why I have not placed it in setup because the application window is only displayed once setup has finished.

1. int fx, fy;
2. 
   
3. public void setup() {
4.   size(300, 300);
5.   print("Monitor display resolution is ");
6.   println(displayWidth + " x " + displayHeight);
7. }
8. 
   
9. public void mouseClicked() {
10.   if (frame != null) {
11.     fx = frame.getLocationOnScreen().x;
12.     fy = frame.getLocationOnScreen().y;
13.     print("Application Window is at [ ");
14.     println(fx + ", " + fy + "]");
15.   }
16. }
17. 
    
18. public void draw() {
19. }

Just tried, adding
println("Application Window is at [ " + frame.getX() + ", " + frame.getY() + "]");
to quarks' sketch display the same thing...
getLocationOnScreen apparently wraps the information from getX/Y() in a vector.