Dispose() and IDisposable

 if we call Dispose() in a class we need to implement IDisposable.. why do we have to do this? implementing an interface is like a contract right? if an interface has some methods and we implement that interface we need to provide implementation to all the methods in that interface.. we can do that without implementing the interface right? is it to make it clear that Dispose method is implemented that we implement IDisposable?

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