Difference between interfaces Comparable and Comparator? (Java)

Question

Main differences between them?
Can be both applied simultaneously to the same class, or are exclusive (excludent?)?

Answer 1

A Comparable class can compare its instances. That is why you can use any sorting methods on this class instances.
A Comparator is a class which can compare instances of an other class. Even if they are not Comparable. Using this method you can compare instances of any class.
Of course a class can implement Comparable and Comparator too but it is useless as these two interfaces are totally different. You should never sort or compare Comparators.