How to Shuffle an Array in Java

There are two ways to shuffle an array in Java.

1. Collections.shuffle() Method
2. Random Class

1. Shuffle Array Elements using Collections Class

We can create a list from the array and then use the Collections class shuffle() method to shuffle its elements. Then convert the list to the original array.

package com.journaldev.examples;

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

public class ShuffleArray {

	public static void main(String[] args) {

		Integer[] intArray = { 1, 2, 3, 4, 5, 6, 7 };

		List<Integer> intList = Arrays.asList(intArray);

		Collections.shuffle(intList);

		intList.toArray(intArray);

		System.out.println(Arrays.toString(intArray));
	}
}

Output: [1, 7, 5, 2, 3, 6, 4] Note that the Arrays.asList() works with an array of objects only. The concept of autoboxing doesn’t work with generics. So you can’t use this way to shuffle an array for primitives.

2. Shuffle Array using Random Class

We can iterate through the array elements in a for loop. Then, we use the Random class to generate a random index number. Then swap the current index element with the randomly generated index element. At the end of the for loop, we will have a randomly shuffled array.

package com.journaldev.examples;

import java.util.Arrays;
import java.util.Random;

public class ShuffleArray {

	public static void main(String[] args) {
		
		int[] array = { 1, 2, 3, 4, 5, 6, 7 };
		
		Random rand = new Random();
		
		for (int i = 0; i < array.length; i++) {
			int randomIndexToSwap = rand.nextInt(array.length);
			int temp = array[randomIndexToSwap];
			array[randomIndexToSwap] = array[i];
			array[i] = temp;
		}
		System.out.println(Arrays.toString(array));
	}
}

Output: [2, 4, 5, 1, 7, 3, 6]