Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Comparison method violates its general contract

Question

Disclaimer: I saw the thread about transitivity of comparison functions, but I don't think mine are bad/I dont see mistake in them

So I wrote a simulation of rabbits and wolfs - there is a set amount of wolves and rabbits in the beginning, rabbits run away from wolfs and wolfs chase rabbits, when they meet in the same block rabbit gets killed and simulation ends when there are no rabbits left.

For small boards, up till about 32x32 all is ok, but for 64+ I get the following error while running.

Also, here are my 3 comparison functions:

lBlocks are JLabels, hare/wolf/killer are icons

public  synchronized boolean isEmpty(int x, int y){
    if(!(lBlocks[x][y].getIcon() instanceof Icon)) return true;
    return false;
}


public  synchronized boolean isWolf(int x, int y){
    if(!(lBlocks[x][y].getIcon() instanceof Icon)) return false;
    if(lBlocks[x][y].getIcon().equals(hare)||lBlocks[x][y].getText().equals("h")||isEmpty(x,y)) return false;
    return true;
}

public  synchronized boolean isHare(int x, int y){
    if(!(lBlocks[x][y].getIcon() instanceof Icon)) return false;
    if(isEmpty(x,y)||isWolf(x,y)) return false;
    return true;
}

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Comparison method violates its general contract!
    at java.util.TimSort.mergeLo(TimSort.java:747)
    at java.util.TimSort.mergeAt(TimSort.java:483)
    at java.util.TimSort.mergeCollapse(TimSort.java:410)
    at java.util.TimSort.sort(TimSort.java:214)
    at java.util.TimSort.sort(TimSort.java:173)
    at java.util.Arrays.sort(Arrays.java:659)
    at java.util.Collections.sort(Collections.java:217)
    at javax.swing.SortingFocusTraversalPolicy.enumerateAndSortCycle(SortingFocusTraversalPolicy.java:136)
    at javax.swing.SortingFocusTraversalPolicy.getFocusTraversalCycle(SortingFocusTraversalPolicy.java:110)
    at javax.swing.SortingFocusTraversalPolicy.getFirstComponent(SortingFocusTraversalPolicy.java:435)
    at javax.swing.LayoutFocusTraversalPolicy.getFirstComponent(LayoutFocusTraversalPolicy.java:166)
    at javax.swing.SortingFocusTraversalPolicy.getDefaultComponent(SortingFocusTraversalPolicy.java:515)
    at javax.swing.SortingFocusTraversalPolicy.getComponentDownCycle(SortingFocusTraversalPolicy.java:204)
    at javax.swing.SortingFocusTraversalPolicy.getFirstComponent(SortingFocusTraversalPolicy.java:447)
    at javax.swing.LayoutFocusTraversalPolicy.getFirstComponent(LayoutFocusTraversalPolicy.java:166)
    at javax.swing.SortingFocusTraversalPolicy.getDefaultComponent(SortingFocusTraversalPolicy.java:515)
    at java.awt.FocusTraversalPolicy.getInitialComponent(FocusTraversalPolicy.java:169)
    at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:380)
    at java.awt.Component.dispatchEventImpl(Component.java:4731)
    at java.awt.Container.dispatchEventImpl(Container.java:2287)
    at java.awt.Window.dispatchEventImpl(Window.java:2719)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:708)
    at java.awt.EventQueue$4.run(EventQueue.java:706)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
    at java.awt.SequencedEvent.dispatch(SequencedEvent.java:128)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:708)
    at java.awt.EventQueue$4.run(EventQueue.java:706)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

The thing is, it does not do absolutely anything - code is working and simulation is going on, but I want to fix it. The worst fact is that there is no line where the error is ocurring and I have a lot of .equals (code is about 400 lines altogether) - I don't know where to find my mistake :(

edit: I found out that if both x and y of board are more than 57 this problem occurs, if they are smaller (or atleast one of them) it does not, lol.

Answer 1

The quick solution appears to be: System.setProperty("java.util.Arrays.useLegacyMergeSort", "true"); According to this answer.