Why override keyword is used to implement abstract method of an abstract class but not to implement interface members?

Question

Look at this code.

 public abstract class Customer { public abstract void Print(); } class Program : Customer { public override void Print() { Console.WriteLine("Print Method"); } }

When we implement an abstract method of abstract class we use override keyword as shown above.

Now look at this code.

 public interface ICustomer { void Print(); } class Program : ICustomer { public void Print() { Console.WriteLine("Print Method"); } }

When we implement a method of an interface we don't use override keyword.Why?

Why we use = to assign a value? Why we use & to perform a binary AND? Why we use || to perform a boolean OR? — Gusman
– Gusman, Commented Feb 1, 2018 at 14:28
I am asking this question because interface members are abstract by default. So for implementing them shouldn't we use override like we do for abstract classes. — gamerdev
– gamerdev, Commented Feb 1, 2018 at 15:57

Patrick Hofman · Accepted Answer · 2018-02-01 14:27:53Z

2

For an interface, there is nothing to override. There is no implementation yet. The CLR doesn't have to walk the class hierarchy to find the class with the appropriate implementation, there is just one.

For abstract methods, there already is an implementation (or definition in the class), and that implementation has to be overriden. That is how the language has been defined.

answered Feb 1, 2018 at 14:27

Patrick Hofman

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4 Comments

Bradley Uffner Over a year ago

Interfaces might be getting default implementations "soon". github.com/dotnet/csharplang/blob/master/proposals/…

gamerdev Over a year ago

But I didn't provide implementation for the abstract method in the class. The method is abstract so what's there to override.

Patrick Hofman Over a year ago

The method is abstract. I guess the current rule is easier from a compiler implementation point of view.

gamerdev Over a year ago

Also interface members are abstract by default. So shouldn't we write override for implementing them.

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