Java Shuffle Array | Random Array Program example

Java Shuffle Array is a procedure to randomize data. As you know Array is a collection of similar types of data like a list of Integers or Strings. The shuffling does randomize the data sets and generating a random data set in the array is different.

This tutorial we will look at both example create a random array and shuffle an array in java.

Java shuffle Array example

One way is to do a shuffled array is using the “Fisher-Yates shuffle” algorithm. This algorithm generates a random number sequence by doing shuffling data without missing anyone from the list.

import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;

public class Hello {
    public static void main(String args[])
    {
        int[] solutionArray = { 1, 2, 3, 4, 5, 6 };

        shuffleArray(solutionArray);
        for (int i = 0; i < solutionArray.length; i++)
        {
            System.out.print(solutionArray[i] + " ");
        }
        System.out.println();
    }

    // Implementing Fisher–Yates shuffle
    static void shuffleArray(int[] ar)
    {
        // If running on Java 6 or older, use `new Random()` on RHS here
        Random rnd = ThreadLocalRandom.current();
        for (int i = ar.length - 1; i > 0; i--)
        {
            int index = rnd.nextInt(i + 1);
            // Simple swap
            int a = ar[index];
            ar[index] = ar[i];
            ar[i] = a;
        }
    }
}

Output: 5 4 1 3 6 2

Shuffle String Array Java

An upper example you saw for Integer Array, the same thing you can do with a String array. See the below example for it. Don’t forget to add the string array parameter in the shuffleArray method.

import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;

public class Hello {
    public static void main(String args[])
    {
        String[] solutionArray = { "A", "B", "C", "D", "E", "F" };

        shuffleArray(solutionArray);
        for (int i = 0; i < solutionArray.length; i++)
        {
            System.out.print(solutionArray[i] + " ");
        }
        System.out.println();
    }

    // Implementing Fisher–Yates shuffle
    static void shuffleArray(String[] ar)
    {
        // If running on Java 6 or older, use `new Random()` on RHS here
        Random rnd = ThreadLocalRandom.current();
        for (int i = ar.length - 1; i > 0; i--)
        {
            int index = rnd.nextInt(i + 1);
            // Simple swap
            String a = ar[index];
            ar[index] = ar[i];
            ar[i] = a;
        }
    }
}

Output: E A B C F D

Shuffle Array with Java Collection.shuffle() method

You can shuffle Array by using the java collection .shuffle() method. For that, you have to use an Integer class and Convert the array into ArrayList. See the example of java shuffle ArrayList.

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class Hello {
    public static void main(String args[]) {
        // Create an array
        Integer[] array = new Integer[]{1, 2, 3, 4};

        //int[] array = new int[]{1, 2, 3, 4}; //does not work

        // Shuffle the elements in the array
        List<Integer> l = Arrays.asList(array);
        System.out.println(l);

        Collections.shuffle(l);

        System.out.println(l);
    }
}

Output: [1, 2, 3, 4]
[4, 2, 1, 3]

Java Random Array

Upper examples you saw shuffling of the Java Array where you have already array then shuffling. What if you want a random array within a range? You can do it with the Random Util class as mentioned below example.

public class Hello {
    public static void main(String args[])
    {
        java.util.Random r = new java.util.Random();
        int[] randomArray = r.ints(0, 10).limit(5).toArray();
        for (int i = randomArray.length - 1; i > 0; i--)
        {
            System.out.print(randomArray[i] + " ");
        }
    }
}

Output: 3 8 2 0

Question: How to shuffle the contents of an array?

Answer: its a very easy as the above-mentioned method Fisher-Yates shuffle or random class. Do comment if you have any other method to do it fast and in efficient ways.

Any doubt and example also commented in below section.

Note: This example (Project) is developed in IntelliJ IDEA 2018.2.6 (Community Edition)
JRE: 11.0.1
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
macOS 10.14.1
Java version 11
All Examples are in Java 11, so it may change on different from Java 9 or 10 or upgraded versions.