should all c# classes implement Equals and GetHashCode?

Question

should all c# classes override Equals and GetHashCode? For correctness

Answer 1

No, they already do.

Whether you have to override them, is up to how it will be used. In most cases, it is not needed.

Answer 2

All classes already inherit these methods from the base class, System.Object.

You can choose to override the methods in derived classes if you need to be able to compare two instances of an object beyond simple reference equality, otherwise it's not necessary.

Remember, however, that if you choose to override one of them, you also need to override the other in order to ensure that Hashtables and dictionary keys, among other things, work properly with you derived class. The GetHashCode method needs to reflect the same logic as the Equals method. See here for more explanations and examples:

http://msdn.microsoft.com/en-us/library/bsc2ak47.aspx

and

http://msdn.microsoft.com/en-us/library/system.object.gethashcode.aspx