Bug 81070 ElementMapper should not use Integer keys computed from System#identityHashCode
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/workingsets/WorkingSetModel.java
public boolean equals(Object o1, Object o2) {
			IWorkingSet w1= o1 instanceof IWorkingSet ? (IWorkingSet)o1 : null;
			IWorkingSet w2= o2 instanceof IWorkingSet ? (IWorkingSet)o2 : null;
			if (w1 == null || w2 == null)
				return o1.equals(o2);
			return w1 == w2;
		}
		public int hashCode(Object element) {
			if (element instanceof IWorkingSet)
				return System.identityHashCode(element);
			return element.hashCode();
		}
	}
	
	private static class ElementMapper {
		private Map fElementToWorkingSet= new HashMap();
		private Map fWorkingSetToElement= new HashMap();
		
		private Map fResourceToWorkingSet= new HashMap();
		public void clear() {
			fElementToWorkingSet.clear();
			fWorkingSetToElement.clear();
			fResourceToWorkingSet.clear();
		}
		public void rebuild(IWorkingSet[] workingSets) {
			clear();
			for (int i= 0; i < workingSets.length; i++) {
				put(workingSets[i]);
			}
		}