- SoftReference: Cleared when GC is response to memory demand. Often used to implement memory-sensitive cache.
- WeakReference: Don’t prevent to be finalized. Often used to implement canonicalizing mapping. (Mapping only reachable object instances)
- PhantomReference: Are enqueued after determining to be reclaimed. Not automatically cleared by GC. Object referenced via phantom reference won’t be cleared by GC automatically until phantom reference cleared.
