question: public final void addReference ( Object ref ) { refSet . add ( ref ) ; }
target:  Adds the given Object to the set of hard references, which will prevent that Object from being disposed until the queue has been flushed completely.  This is useful in cases where some enqueued data could become invalid if the reference Object were garbage collected before the queue could be processed.  (For example, keeping a hard reference to a FontStrike will prevent any enqueued glyph images associated with that strike from becoming invalid before the queue is flushed.)  The reference set will be cleared immediately after the queue is flushed each time.