Why is it not allowed to narrow down scope of a method while overriding

Question

In Java, when I override a method the compiler flags off any attempt to narrow down the visibility as an error. For ex: I can\'t override a public method as protected, while

Answer 1

Consider a class B which inherits from A. A.m() is public. Now consider this code:

A obj = new B();
obj.m();

Should this call be allowed? Yes, it should, because obj is an object of type A! It is also an object of type B, but that is not necessarily known to the one using the object.

Every object of type A must adhere to the contract (interface) for A. B extends A and must therefore also adhere to that contract.