Proper use of the Java Weak Reference for nested collections

Question

I need to define a weak reference map whose value is Set. I use MapMaker for Google collections, for example:

Map<Class<? extends Object>, Set<Foo>> map = new MapMaker().weakKeys().weakValues().makeMap();

So, Set<Foo>can one use regular HashSet? Or I need to create a weak HashSet, for example:

Collections.newSetFromMap(new WeakHashMap<Foo, Boolean>());

And why?

Another question, my card key is class objects, when will the class object become inaccessible? In other words, what is the lifetime of a class object?

Thank.

Update: The first question is not entirely clear. My concern was that when I do map.get(key).add(foo)to add an instance of foo to Set, it will also add a strong reference to the instance of foo and thus prevent its GCed? That's why I was wondering if a weak HashSet should be used.

Answer 1

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