Sorting in HashSet

Question

I read that java.util.HashSet doesn't sort. However when I execute this code

import java.util.*; 

public class Example {  
    public static void main(String[] args) { 
        Set set = new HashSet();  
        set.add(newInteger(5));  
        set.add(new Integer(2)); 
        set.add(new Integer(1)); 

        System.out.println(set);
    }
}

the output is

[1, 2, 5]

Why are the values sorted?

Java has a documentation feature called `javadoc`. Read `HashSet`'s javadoc. — Sotirios Delimanolis, Feb 14 '14 at 00:35
... and it happens by chance to come out in numerical order. — rgettman, Feb 14 '14 at 00:35
Your sample size is very small. Try lots of items in your set. Also, try strings instead of ints. Behaviour will become apparent. — Paul Hicks, Feb 14 '14 at 00:39

xlm · Answer 1 · 2014-02-14T00:53:22.303

There is no guarantee that it will always be in order. As already stated helpfully in the comments, it just so happens by chance that in this case does and if you are interested why check the Javadoc.

Essentially it uses a hash function (as you may have guessed by HashSet) to map the value to a particular 'bucket' or position in memory for fast look up (i.e. check set membership etc.). A simple example would be where it takes the value mod some number (i.e. number of 'buckets') to determine which 'bucket' to store the value which in your case is most likely is larger than the values of your added integers, hence they are placed in order.

Sorting in HashSet

1 Answers1