方法重写：Rules for method overriding

https://www.geeksforgeeks.org/overriding-in-java/

Overriding and Access-Modifiers :

Final methods can not be overridden :

Static methods can not be overridden(Method Overriding vs Method Hiding)

Private methods can not be overridden

The overriding method must have same return type (or subtype) :

Overriding and Exception-Handling

Rule#1 :

如果超类重写方法没有抛出异常，子类重写方法只能抛出 unchecked exception，
抛出 checked exception 将导致编译时错误。

Rule#2 :

If the super-class overridden method does throws an exception, subclass overriding method can only throw same, subclass exception.

Overriding and synchronized/strictfp method

对方法重写没有任何影响：
synchronized / strictfp方法可能会覆盖非synchronized / strictfp方法，反之亦然。