Question

I want to know if i don’t put override key word before the method in derived class method m1(), then what is the default value before this, or will it throw a compile time error?

class A { virtual void m1(){} }
class B: A { void m1(){} }

Answer 1

First, you’ll get a compile-time error because virtual members can not be private which A.m1 is as written.

Second, once you fix this, you’ll get a compile-time warning that B.m1 hides the inherited member A.m1.

Third, if you do something like this:

A a = new B();
a.m1();

This will invoke A.m1 whereas if you insert override into the definition of B.m1 then the above will invoke B.m1. However, if you insert new into the definition of B.m1 then the above will still invoke A.m1 but it will omit the compile-time warning.