Java Doc for WeakHashSet.java in  » Content-Management-System » harmonise » oreilly » hcj » references » Java Source Code / Java DocumentationJava Source Code and Java Documentation

Uses the WeakHashMap class as a backing store to implement a set of objects that are stored as weak references. All information concerning using keys in the WeakHashMap class pertain to this class and it is reccomended that the user of this class review that material before using the class.

Because this set contains only weak references, it is not serializable. If one tried to serialize a weak reference, the results would be highly unpredictable as the object could likely vanish from memory before the proces was even completed. Users of this class must use transient when the containing class uses this set.

Because of the semantics of the weak references, the value null is not allowed in this set.

This collection is not identity based but equality based. This can cause some confusion as you cannot put in two objects whose equals() methods return true. It also means that an object being held is not necessarily the same one that the user is holding. For example, you could have a String with the value 'fred' at memory location X and ther could be another String with the value 'fred' at memory location Y. The first instance is in the set but the second isn't.

Gives back the hashCode for the backing store key set.

Note that this iterator is extremely volatile because the user may iterate over an element in the set and find seconds later that it has been removed.

Gives back the hashCode for the backing store key set. The user should be aware, however, that this hash code can change without user intervention as the objects in the collection can easily be collected microseconds after completetion of the method. It is not reccomended that the user rely on this hash code for consistency

Note that this iterator is extremely volatile because the user may iterate over an element in the set and find seconds later that it has been removed. This is because of the semantics of weak references which act like a second thread is silently modifying the collection. For this reason, it is advisable that if the user wants to do something with the set that they maintain a strong reference to the object and not rely on it being in the collection for them.

This iterator is fail fast and WeakReference transparrent. By this we mean that the iterator simply ignores objects pending in the reference queue for cleanup.