Chooses and returns the representative instance for any of a collection of
instances that are equal to each other. If two equal inputs are given to this method, both calls will return the same
instance. That is, intern(a).equals(a) always holds, and intern(a) == intern(b) if and only if a.equals(b). Note that
intern(a) is permitted to return one instance now and a different
instance later if the original interned instance was garbage-collected.