ConcreteClassOnlyImplementDirectAbstract
DRAFT

Incorrect

A concrete class only needs to implement abstract methods declared in its direct supertypes

Correct

Correction
Here is what's right.

It has to implement all abstract methods declared in any of its supertypes, even if they are declared in a supertype of a supertype (e.g., declared in an interface that is extended by the interface the concrete class implements).

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