HashMap & HashSet size() in Java

Question

I tried to find information about it but failed.

How is size() in HashMap or HashSet implemented? How does it work? Is it an O(1) or O(n) operation?

The source code is open, you can have a look: grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/… — Alexis C., Commented Jan 25, 2018 at 12:43

Eran · Accepted Answer · 2018-01-25 12:44:36Z

6

It takes O(1) time. HashMap has a size instance variable that gets modified when entries are added or removed:

This is the HashMap implementation:

/**
 * Returns the number of key-value mappings in this map.
 *
 * @return the number of key-value mappings in this map
 */
public int size() {
    return size;
}

HashSet calls size() of the backing HashMap.

answered Jan 25, 2018 at 12:44

Eran

395k5757 gold badges726726 silver badges792792 bronze badges

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

1 Comment

leocrimson Over a year ago

Thanks for quick response and sharing the resource.

Collectives™ on Stack Overflow

HashMap & HashSet size() in Java

1 Answer 1

1 Comment

Your Answer

Post as a guest

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Post as a guest

Related