Why there is no WeakList and WeakSet implementation in Java? [duplicate]

Question

... at least not "official".

You can easily google two or three "WeakList" example implementation and for "WeakSet" one very good can be found in NetBeans Platform API sources.

I read similar question placed here asking for WeakSet. Answers were "there is no usecase for WeakSet". If it will be like this why these unofficial implementations exist?

Answer 1

Perhaps you can get one by using Collections.newSetFromMap(new WeakHashMap()). Many collections don't exist as public classes (if they are not-so-important), but can be obtained by the Collections factory methods.