Question

public int Add(int a, int b) 
public float Add(int a, int b) 

returned type is different.

is this overloading or overriding ?

and what if access type is different

public int Add(int a, int b) 
private int Add(int a, int b)

Can you help me?

Answer 1

It’s neither: it’s invalid code. You can’t create two methods which differ only by return type. (Or by return type and access modifier…)

If you could, it would be overloading though – overriding happens across the inheritance hierarchy, where a method in a derived class overrides a virtual method declared in a base class. In this case, you’ve given no indication that they’re in different classes.

The biggest difference between overloading and overriding is when the decision is made about which method to use: the compiler picks the signature based on the compile-time types, and then the implementation is chosen based on the execution-time type of the actual object.

So if method Derived.M(int) overrides Base.M(int), then the compiler doesn’t care – it just knows it’s calling Base.M(int) and lets the CLR take care of the virtual dispatch.

However, if there are methods Foo.M(int) and Foo.M(float) then the compiler decides at compile-time which of those will be used. (Of course, they could be virtual with overrides involved as well.)

It’s worth noting that overloading across an inheritance hierarchy can be interesting, too – I’ve got a whole article about overloading which lists some of the oddities you might come across.