An object performing equality comparisons, along with a hash
function consistent with this comparison. The type signatures
of the methods of this interface reflect those of java.util.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.
Returns true if the given objects are considered equal. This function must obey an equivalence relation: equal(a, a) is always true, equal(a, b) implies equal(b, a), and (equal(a, b) && equal(b, c) implies equal(a, c). Note that the second argument need not be known to have the same declared type as the first.
key - a key in, or being placed in, the mapx - an object queried for membershipReturns a hash value such that equal(a, b) implies hash(a)==hash(b).
x - an object queried for membership