public UnionSet(IObservableSet[] childSets, Object elementType) {
super(childSets[0].getRealm(), null, elementType);
System.arraycopy(childSets, 0,
this.childSets = new IObservableSet[childSets.length], 0,
childSets.length);
this.stalenessTracker = new StalenessTracker(childSets,
stalenessConsumer);
}