This comparator's general contract is broken for the case where both
node1 and node2 have negative source indexes. In that case the returned
results are:
- (node1, node2) => -1
- (node2, node1) => -1
which is not symmetric, as is expected by the Comparator interface.
This is noticed by the TimSort implementation when sorting:
12:59:34.108 SEVERE: [38] util.UtilActivator.uncaughtException().108 An uncaught exception occurred in thread=Thread[AWT-EventQueue-0,6,main] and message was: Comparison method violates its general contract! java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.util.TimSort.mergeHi(TimSort.java:868)
at java.util.TimSort.mergeAt(TimSort.java:485)
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 net.java.sip.communicator.impl.gui.main.contactlist.GroupNode$1.run(GroupNode.java:323)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:312)
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.awt.EventQueue.dispatchEvent(EventQueue.java:703)
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)
This proposition tries to distinguish between two nodes by comparing
their hashCode value. This is kind of a work around, however, since this
is already a special case it should not matter that much. Since the
hashCode is a comparable value we can ensure that we make a consistent,
symmetric choice every time. Thus enforcing the contract.