Why can abstract methods only be declared in abstract classes?

Question

I understand that in abstract classes methods be both abstract, or not. But why can I not create an abstract method in a "normal", non-abstract class?

Thanks in advance for any explanation!

Answer 1

Abstract method basically says, that there is no implementation of the method and it needs to be implemented in a subclass. However if you had an abstract method in a non-abstract class, you could instantiate the class and get an object, that would have an unimplemented method, which you would be unable to call.

Answer 2

Having an abstract method prevents a class from being instantiated, thus making it a de-facto abstract class. Java insists on you declaring this fact explicitly for consistency: technically, Java compiler does not need this additional mark in order to decide if a class is abstract based on the presence of abstract methods, but since you may want to make a class abstract without making any of its methods abstract, requiring the declaration on the class was the way to go.