Java program to shuffle an array using list

In this article, we will learn how to shuffle an array using a list in Java. To do so, we will be using:

• Using Collections.shuffle() Method
• Using Fisher-Yates shuffle
• Using Java Streams

Using Collections.shuffle() Method

Shuffling an array means randomly rearranging its elements. The Java Collections framework provides the Collections.shuffle() Method, which shuffles a list. Since this method shuffles the list randomly, the order of the resultant elements is different each time we use it.

Example

Following is the program to shuffle an array using a list:

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
public class Demo {
   public static void main(String[] args) {
      String str[] = {"A", "B", "C", "D", "E"};
      List<String>list = Arrays.asList(str);
      Collections.shuffle(list);
      System.out.println("Shuffled the array using List = "+list.toString());
   }
}

Following is the output of the above program:

Shuffled the array using List = [C, B, E, D, A]

Using Fisher-Yates Shuffle 

We can also implement our custom algorithm to shuffle the elements of a list. One simple and effective algorithm is the Fisher-Yates shuffle.

In this algorithm, we loop through the list from the last element to the first, and for each element, we swap it with a randomly selected element from the range 0 to the current index (inclusive). This gives us a well-randomized list.

Example

Following is an example to shuffle an array using a list by implementing the Fisher-Yates shuffle:

import java.util.*;
public class Demo {
   public static void main(String[] args) {
      List<String> list = new ArrayList<>(Arrays.asList("A", "B", "C", "D", "E"));
      Random rand = new Random();
      for (int i = list.size() - 1; i > 0; i--) {
         int j = rand.nextInt(i + 1);
         String temp = list.get(i);
         list.set(i, list.get(j));
         list.set(j, temp);
      }
      System.out.println("Shuffled list: " + list);
   }
}

Following is the output of the above program:

Shuffled list: [D, B, A, C, E]

Using Java Streams

We can also shuffle the elements of a list using the Stream API. First, we convert the list into a stream, collect the elements into a new list. Invoke the Collections.shuffle() method on the newly obtained list.

This approach gives us a shuffled copy of the original list without changing it.

Example

In the following example, we will create a list and then shuffle its elements using the Stream API:

import java.util.*;
import java.util.stream.Collectors;
public class Demo {
   public static void main(String[] args) {
      List<String> list = Arrays.asList("A", "B", "C", "D", "E");
      List<String> shuffled = list.stream()
      .collect(Collectors.collectingAndThen(
         Collectors.toList(), collected -> {
            Collections.shuffle(collected);
            return collected;
         }
      ));
      System.out.println("Shuffled list using streams: " + shuffled);
   }
}

Following is the output of the above program:

Shuffled list using streams: [C, E, D, B, A]