DRAFT
Observed
ConcreteClassMustOverride
Incorrect
A concrete class needs to implement all abstract methods and override all concrete methods declared in its abstract superclasses
Correct
A concrete class does not necessarily need to override concrete methods declared in its abstract superclasses
CorrectionHere is what's right.
Here is what's right.
The concrete class only needs to implement the abstract methods it inherits from its superclasses. If a method is already implemented in its superclasses, the concrete class does not need to implement it again. It simply inherits the implementation from the superclass (even if that superclass is abstract).
Note that abstract classes can have concrete methods.
Language
Java