Why is it not necessary to override both methods of interface Comparator in Java

Question

We know that it is necessary to implement all methods of an interface, if we want to make an object of that class. But why is it not necessary to implement both the methods compare() and equals() of interface Comparator in java?

I agree that the purpose is solved but even then why is it not mandatory to override equals() if we override compare()?

Answer 1

Since all classes implicitly extend Object every implementation of a Comparator has an equals method, because every Object has one.

It would be the same if you define an interface with a toString() method.

 public interface ToString {
      public String toString();
 }

 public class SomeClass implements ToString {
     // toString implicitly implemented, because Object defines it
 }

When you look at the class it says "implements ToString" and this is true, isn't it?