Comparable interface contains only one method compareTo(T o)and for example Collections.sort() method first type-cast the compared object to Comparable and then compares it.
Now I am unable to understand why we need this process in the first place. Wouldn't it be just simpler to call directly compareTo() method of the object and get rid of the Comparable interface? If the object doesn't have compareTo() method it would raise an error anyway just like it does if the object didn't implement Comparable interface.
Besides I don't see a reason one would need a Comparable type object. Is there any advantages of having a Comparable interface ?
If you're only calling compareTo yourself, then it's true that there's no particular reason to implement Comparable.
But for things like Collections.sort and TreeSet, those aren't hardcoded for a specific type, but they have to be able to call compareTo on the objects you pass it to. That's what the Comparable interface is before: implementing Comparable means that Collections.sort and TreeSet know that the objects you pass them will have that method to be called. Implementing Comparable means you can use all of the utilities that exist that need to order objects in any way, and those utilities know how to interact with your objects.