子类Java的超类方法

Question

Does a subclass need to rewrite each method of the superclass or it isn't mandatory to do so but the subclass can override some methodes of the superclass. I am a bit confused.

Answer 1

Subclasses are not required to override any parent methods, even though they can. The only way to force a child class to override a method is to make that method abstract (and the parent class has to be abstract as well).

Answer 2

If a subclass wishes to introduce unique behavior for invocation of a method that it inherited, then that method must be overridden.

The most common cases for this: toString , equals and hashCode are all eligible to be overridden for all of your custom classes, given that your custom class doesn't want to leverage Object#toString , Object#equals or Object#hashCode , which are all "unhelpful" for your custom implementations.

If a subclass does not wish to introduce unique behavior for invocation of a method that it inherited, then this is unnecessary. You can rely on the parent class' behavior instead.

If your parent class is abstract , then you have no choice but to implement what methods the parent class chose not to implement.

If you're implementing an interface, the same principle as abstract classes applies - because the interface does not implement anything itself, you must implement the methods that the interface prescribes.