Java - get random element from HashSet

In this article, we would like to show you how to get a random element from HashSet in Java.

1. Using for loop

In this example, we generate a random number between 0 and HashSet size. Then we iterate through the HashSet till we reach the element located at the randomNumber position.

import java.util.*;

public class Example {

    public static void main(String[] args) {
        Set<String> letters = new HashSet<>();

        letters.add("A");
        letters.add("B");
        letters.add("C");
        letters.add("D");
        letters.add("E");

        int size = letters.size();
        int randomNumber = new Random().nextInt(size);
        int i = 0;

        for (String letter : letters) {
            if (i == randomNumber)
                System.out.println(letter);
            i++;
        }
    }
}

Output:

B

2. Using iterator

In this example, we generate a random number between 0 and HashSet size. Then using iterator we iterate through the HashSet till we reach the element located at the randomNumber position.

import java.util.*;

public class Example {

    public static void main(String[] args) {
        Set<String> letters = new HashSet<>();

        letters.add("A");
        letters.add("B");
        letters.add("C");
        letters.add("D");
        letters.add("E");

        System.out.println(getRandomElement(letters));
    }

    private static <String> String getRandomElement(Set<String> hashset) {
        int randomNumber = new Random().nextInt(hashset.size());  // generate random number

        Iterator<String> iterator = hashset.iterator();

        int index = 0;                  // current index
        String randomElement = null;    // random element to return

        while (iterator.hasNext()) {

            randomElement = iterator.next();


            if (index == randomNumber)  // if current index is equal to random number
                return randomElement;

            index++;
        }

        return randomElement;
    }
}

Output:

E

3. By converting HashSet to Array

In this example, we convert numbers HashSet into an array and then access the random element from it.

import java.util.*;

public class Example {

    public static void main(String[] args) {
        Set<Integer> numbers = new HashSet<>();

        numbers.add(1);
        numbers.add(2);
        numbers.add(3);
        numbers.add(4);
        numbers.add(5);

        Integer[] lettersArray = numbers.toArray(new Integer[numbers.size()]);

        int randomNumber = new Random().nextInt(numbers.size());

        System.out.println(lettersArray[randomNumber]);
    }
}

Output:

2