Question

Would this be a good idea? How can it be solved, if not, nowadays?

I think it would be interesting adding an

final boolean identical(Obj obj){
   return (this==obj);
}

so we had an improved equals (logical equals)

boolean equals (Obj obj){
   return identical(obj); // by default, but its overrideable
}

This question arised from the need in this other question (A Mechanism for having different equals (physical equals and logical equals) on objects in Collection) of having a way to compare a list of identical pointers to a list of equally objects. With that idea we could add to the Collection interface:

 coll.equals(coll2)
 coll.identical(coll2)
 coll.identicalElem(coll2){
      //current equals implementation of collections but calling identical to compare objects
 }

What do you think?

Answer 1

The default equals() implementation you posted is already the one in java.lang.Object. There’s no real point in overriding it with the same implementation.

Regarding your 3 methods to add to the collection interface:

coll.equals(coll2): this one is already in the Collection interface.

coll.identical(coll2): equivalent to coll == coll2, but less readable. I don’t see the point of such a method.

coll.identicalElem(coll2): this method indeed doesn’t exist, but I’ve never had the need for such a method, so I think it should not clutter the API of Collection. You could use Guava’s Equivalence to do that:

Equivalence.identity().pairWise().equivalent(coll1, coll2);