public static interface CustomConcurrentHashMap.Equivalence<K>
Map: While only elements of K may be
entered into a Map, any Object may be tested for
membership. Note that the performance of hash maps is heavily
dependent on the quality of hash functions.boolean equal(K key, java.lang.Object x)
key - a key in, or being placed in, the mapx - an object queried for membershipint hash(java.lang.Object x)
x - an object queried for membership