Method overriding rule important

 1. return type can be different  ,  if they return a subtype like parent class return type Number and child class Integer.

2.Another worth noting rule of method overriding in Java is that the overriding  method can not throw checked Exception which is higher in the hierarchy than the overridden method. This means if the overridden method throws IOException than the overriding method can not throw java.lang.Exception in its throws clause because of java.lang.Exception comes higher than IOException in Exception hierarchy. 

3. You can not override private, static and final the method in Java. private and static method are bonded during compile time using static binding in Java and doesn't resolve during runtime. the overriding the final method in Java is a compile-time error. Though private and static methods can be hidden if you declare another method with the same and signature in the subclass.

4.to override a method in Java is that the overriding method can not reduce the accessibility of the overridden method in Java. For example, if the overridden method is public than the overriding method can not be protected, private or package-private