Why does Java's TreeSet<E> remove(Object) not take an E

Question

From the Java 6 TreeSet<E> Documentation:

boolean remove(Object o):
    Removes the specified element from this set if it is present.

Why does this accept an Object instead of the generic type E? The only objects that can be added are of type E, so it follows that the only removable type should be of type E.

Answer 1

Taking the answer from the first comment posted:

Myth:

A popular myth is that it is stupid and evil, but it was necessary because of backward compatibility. But the compatibility argument is irrelevant; the API is correct whether you consider compatibility or not.

Real reason:

Uniformly, methods of the Java Collections Framework (and the Google Collections Library too) never restrict the types of their parameters except when it's necessary to prevent the collection from getting broken.

Read more here: Why does Set.contains() take an Object, not an E?

Answer 2

remove(), like get() is required to work when given an equal element (in terms of .equals()). In Java, it is possible (and in some cases, required) for objects of different classes to be equal. Hence, you shouldn't restrict the type.