Is there java.util.concurrent equivalent for WeakHashMap?

Solution 1:

Guava's CacheBuilder class allows you to do this easily.

CacheBuilder.newBuilder().weakKeys().build()

Note that this changes key equality semantics to be == instead of .equals() which will not matter in your case of using Class instances but is a potential pitfall.

Solution 2:

I don't believe there is. In fact the javadoc suggests using Collections.synchronizedMap()

"Like most collection classes, this class is not synchronized. A synchronized WeakHashMap may be constructed using the Collections.synchronizedMap method."