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
fWorkingSetManagerListener= new IPropertyChangeListener() {
			public void propertyChange(PropertyChangeEvent event) {
				workingSetManagerChanged(event);
			}
		};
		PlatformUI.getWorkbench().getWorkingSetManager().addPropertyChangeListener(fWorkingSetManagerListener);
		fLocalWorkingSetManager.addPropertyChangeListener(fWorkingSetManagerListener);
	}
	
	public void dispose() {
		if (fWorkingSetManagerListener != null) {
			PlatformUI.getWorkbench().getWorkingSetManager().removePropertyChangeListener(fWorkingSetManagerListener);
			fLocalWorkingSetManager.removePropertyChangeListener(fWorkingSetManagerListener);
			fLocalWorkingSetManager.dispose();
			fWorkingSetManagerListener= null;
		}
	}
	
	
	
    public Object[] getChildren(IWorkingSet workingSet) {
    	return workingSet.getElements();
    }
    
    public Object getParent(Object element) {
    	if (element instanceof IWorkingSet && fActiveWorkingSets.contains(element))
    		return this;
    	return fElementMapper.getFirstWorkingSet(element);
    }