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when to implement comparable and when to implement equals in Java

In Java, when should I implement Comparable<Something> versus implementing the equals method? I understand every time I implement equals I also have to implement hash code.

EDIT

Based on answers I am getting below:

Is it safe to say that if I implement Comparable then I don't need to implement equals and hashCode? As in: whatever I can accomplish with equal is already included in compareTo? For an example, I want to be able to compare two BSTs for equality. Implementing a hashCode for that seems daunting; so would comparable be sufficient?

Solution

  • If you only ever need to compare them for equality (or put them in a HashMap or HashSet which is effectively the same) you only need to implement equals and hashcode.

    If your objects have an implicit order and you indend to sort them (or put them in a TreeMap or TreeSet which is effectively sorting) then you must implement Comparable or provide a Comparator.