There is no Array class in Java (other than in reflections). Arrays are "primitives" of a sort in Java and play by different rules from declared classes.
Certainly a length() method could have been defined on arrays, but the designers wanted to keep length as a property rather than a pseudo-method. (In part this may have made it easier for early Java implementations.) The reasons are somewhat buried in history.
(A better question is why Java couldn't decide whether to call the concept "length", "count", or "size" -- I always end up trying all three before I hit on the right one for an aggregating class.)
