What are covariant return types, and what rules constrain an overriding method's signature, exceptions, and visibility?

An override may return a subtype of the original return type (covariant returns), which is why a clone() override can return the concrete type.

The override cannot reduce visibility (a public method can't become protected), cannot throw broader or new checked exceptions than the parent declared, and must keep the same parameter list or it becomes an overload instead. @Override is worth using because it makes the compiler catch a signature mismatch that would otherwise silently create an overload.