Adding elements into HashSet

Question

I have a question about how add method in the HashSet works. I am relatively new to Java so please don't mind if this too naive. I was looking into the source code for HashSet and found that the 'add' method in the HashSet is saving the values in a HashMap.

public boolean More ...add(E e) { return map.put(e, PRESENT)==null; }

What I figured out is that the 'e' is the key and the add method adds the new element as a key and not as a value and thus the HashSet will have no duplicates.Please correct me if I am wrong.

You are right. I know the excitement of looking at Java source code is uncontrollable at times but seriously, what's the question now? — Chetan Kinger
– Chetan Kinger, Commented Jun 2, 2015 at 13:00
You know it already... If you want to dig deep... Follow the link... javahungry.blogspot.com/2013/08/… — CoderNeji
– CoderNeji, Commented Jun 2, 2015 at 13:01
That's basically correct. It just uses the same value PRESENT for all the entries. Nobody cared to create a separate hash set implementation, instead the existing HashMap code was reused (even though it takes more memory to store those references to the PRESENT object). — Tagir Valeev
– Tagir Valeev, Commented Jun 2, 2015 at 13:01
Good job for actually going into core java code yourself to see what is going on. — vikingsteve
– vikingsteve, Commented Jun 2, 2015 at 13:04
@DhrubojyotiBhattacharjee Yes, that's essentially what happens - PRESENT is used as a dummy value. — Jesper
– Jesper, Commented Jun 2, 2015 at 13:06

Community · Accepted Answer · 2017-05-23 11:51:07Z

2

Yes, you are correct. The answers to this SO question go into more detail:

Internal implementation of java.util.HashMap and HashSet

edited May 23, 2017 at 11:51

CommunityBot

11 silver badge

answered Jun 2, 2015 at 13:05

Paul

20.2k15 gold badges84 silver badges100 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Adding elements into HashSet

1 Answer 1

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Linked

Related