The origin of the problem
Array-based collections realized on exit element, does not take a reference point to a null pointer, outdated reference object exists would not have been recovered.
Measure
Wherein when the key 1.WeakHashMap when no longer referenced externally, will be recovered. ThreadLocal uses WeakHashMap
2.LinkedHashMap of removeEldestEntry method:
By covering this method, addition of certain conditions, the condition returns true. When put into the new value method returns true, then remove the oldest map key.
3.java.lang.ref:
Strong Reference
Soft Reference
Weak Reference
Phantom Reference
4. Analysis by Heap Profiler