When should a class be Comparable and/or Comparator?

Question

I have seen classes which implement both Comparable and Comparator. What does this mean? Why would I use one over the other?

Answer 1

java.lang.Comparable

1. To implement Comparable interface, class must implement a single method compareTo()

   int a.compareTo(b)

2. You must modify the class whose instance you want to sort. So that only one sort sequence can be created per class.

java.util.Comparator

1. To implement Comparator interface, class must implement a single method compare()

   int compare (a,b)

2. You build a class separate from class whose instance you want to sort. So that multiple sort sequence can be created per class.