No support for unsigned integers (Other than char).
int test = new int[-1]; // Negative sized Array Exception
IdentityHashMap: violates Map contracts by using reference equality (not .equls()) during put/get operations
Math.abs() returns absolute value except if the argument is equal to the value of Long.MIN_VALUE, the most negative long value, the result is that same value, which is negative (This is due to overflow).
You cannot initialize static final field with in constructor, because construtor is called for every instance created and the static final field will get initialized on every instance. [this is obvious but you still can’t, even if your intent is to create a single instance by making the constructor private, ofcourse you still can create multiple instances with in the declaring class.]
Unlike HashMap Concurrent Hash Map (CHM) & ConcurrentSkipListMap (CSLM) doesn’t take null keys or values. http://cs.oswego.edu/pipermail/concurrency-interest/2006-May/002485.html.
null is not an instanceof any java type.