How to get a random element from Set?

Problem statement

Get a random element from the set.

 

Solution

Step 1: Get a random number ‘n’ between 1 and set.size.

Integer randPosition = new SecureRandom().nextInt(set.size());

 

Step 2: Iterate over the set and return the number at nth iteration.

 

Find the below working application.

 

SetUtil.java

package com.sample.app.reflections;

import java.security.SecureRandom;
import java.util.Iterator;
import java.util.Set;

public class SetUtil {

    public static <T> T randomElement(Set<T> set) {

        if (set == null || set.isEmpty()) {
            return null;
        }

        Integer randPosition = new SecureRandom().nextInt(set.size());

        Iterator<T> iter = set.iterator();

        int counter = 0;
        while (iter.hasNext()) {

            if (counter == randPosition) {
                return iter.next();
            }
            iter.next();
            counter++;

        }

        return null;
    }

}

 

App.java

package com.sample.app;

import java.util.HashSet;
import java.util.Set;

import com.sample.app.reflections.SetUtil;

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

        primes.add(2);
        primes.add(3);
        primes.add(5);
        primes.add(7);
        primes.add(11);
        primes.add(13);
        primes.add(17);
        primes.add(19);
        primes.add(23);
        primes.add(29);

        for (int i = 0; i < 10; i++) {
            System.out.println(SetUtil.randomElement(primes));
        }

    }
}

  Sample Output

 

17
11
7
5
17
17
23
29
7
7

 

 

 

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