Why do we have contains(Object o) instead of contains(E e)?

Question

Is it to maintain backwards compatibility with older (un-genericized) versions of Collection? Or is there a more subtle detail that I am missing? I see this pat

Answer 1

It is because the contains function utilizes the equals function, and the equals function is defined in the base Object class with a signature of equals(Object o) rather than equals(E e) (since not all classes are generic). Same case with the remove function - it traverses the collection using the equals function which takes an Object argument.

This doesn't directly explain the decision however, as they could've still used type E and allowed it to be automatically cast to type Object on the call to equals; but I imagine they wanted to allow the function to be called on other Object types. There's nothing wrong with having a Collection c; and then calling c.contains(somethingOfTypeBar) - it will always return false, and so it eliminates the need for a cast to type Foo (which can throw an exception) or, to protect from the exception, a typeof call. So you can imagine if you're iterating over something with mixed types and calling contains on each of the elements, you can simply use the contains function on all of them rather than needing guards.

It's actually reminiscent of the "newer" loosely-typed languages, when you look at it that way...