I'm running a simple test app that is posting an error apparently from a windowing routine in MacOS's Cocoa system library.

1. import java.awt.*;
2. int[] pts1 = { 0,0, 1,1, 2,1, 3,2, 3,1, 3,0, 2,0, 1,0, 0,0 };
3. int[] pts2 = { 3,0, 3,1, 3,2, 3,3, 4,2, 4,1, 3,0 };
4. Point[] arr1;
5. Point[] arr2;
6. 
   
7. void setup() {
8.   size(481, 481);
9.   background(255);
10.   arr1 = arrayAsPoints(pts1);
11.   arr2 = arrayAsPoints(pts2);
12.   noLoop();
13. }
14. 
    
15. void draw() {
16.   println("area 1 = " + area(arr1));
17.   println("area 2 = " + area(arr2));
18. }
19. 
    
20. /**
21.  * outputs 2 * area of polygon, negative if vertices are in CCW order.
22.  */
23. float area(Point[] coords) {
24.   int len = coords.length;
25.   float result = coords[0].x * (coords[1].y - coords[len-2].y);
26.   for (int i = 1; i < len - 1; i++) {
27.     result += coords[i].x * (coords[(i+1) % len].y - coords[i-1].y);
28.   }
29.   return result;
30. }
31. 
    
32. Point[] arrayAsPoints( int[] arr ) {
33.   Point[] ptArray = new Point[arr.length/2];
34.   int index = 0;
35.   for ( int i = 0; i < arr.length; i += 2 ) {
36.     ptArray[index] = new Point( arr[i], arr[i+1] );
37.     index++;
38.   }
39.   return ptArray;
40. }

Not much going on there, as you can see--just a test for an area calculation.

Here's the error, followed by the application output:

2010-06-23 08:31:08.569 java[899:170f] *** Assertion failure in -[CocoaAppWindow _changeJustMain], /SourceCache/AppKit/AppKit-1038.32/AppKit.subproj/NSWindow.m:9470
2010-06-23 08:31:08.571 java[899:170f] *** CPerformer: ignoring exception 'Invalid parameter not satisfying: [self canBecomeMainWindow]' raised during perform of selector 'requestFocus:' on target 'FocusManager' with args '<AWTComponentSetFocusData: 0x1205040>'
area 1 = -6.0
area 2 = -4.0

The error doesn't seem to cause any problems, since it gets ignored. I've seen it before. Maybe there's no need to avoid it, if it's really innocuous, but I can't help but wonder why it occurs and if I can prevent it.

cheers,

--Paul