When should a class be Comparable and/or Comparator?

The text below comes from Comparator vs Comparable

Comparable

A comparable object is capable of comparing itself with another object. The class itself must implements the java.lang.Comparable interface in order to be able to compare its instances.

Comparator

A comparator object is capable of comparing two different objects. The class is not comparing its instances, but some other class’s instances. This comparator class must implement the java.util.Comparator interface.

Implementing Comparable means "I can compare myself with another object." This is typically useful when there's a single natural default comparison.

Implementing Comparator means "I can compare two other objects." This is typically useful when there are multiple ways of comparing two instances of a type - e.g. you could compare people by age, name etc.