What is the purpose of having equals(Object obj) in java 8 Comparator

According to This SO Question, I understand that a Functional Interface can have abstract method/s overriding one or more of the public methods of java.lang.Object.

If they have declared Object's method in Comparator why not in any other Functional Interface (java.lang.function)?

However, my question is that why java engineers declare it explicitly in Comparator interface only and what is the use of it?