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Java - get random element from HashSet

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Created by:

Peter-Mortensen

558

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

1. Using for loop

Edit

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.

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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:

xxxxxxxxxx
 
B

2. Using iterator

Edit

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.

xxxxxxxxxx
 
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:

xxxxxxxxxx
 
E

3. By converting HashSet to Array

Edit

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

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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]);
    }
}