How to use the Collections.shuffle method in Java
The Collections.shuffle method is defined in Java’s built-in java.util.Collections class. As its name suggests, the method shuffles the elements of a given list by randomly permuting them.
Code
The following code snippet creates a list of strings and then shuffles them randomly using Collections.shuffle:
import java.util.*;class Program {public static void main( String args[] ) {List<String> myList = new ArrayList<String>();myList.add("Hippo");myList.add("Panda");myList.add("Brown Bear");myList.add("Koala");myList.add("Polar Bear");System.out.println("Original list: " + myList);// Randomly shuffle the list.Collections.shuffle(myList);System.out.println("List after shuffle: " + myList);}}
One can also define the degree of randomness with which the elements are shuffled. This can be used to make shuffling a deterministic process (if that is a requirement for the program). Hence, when the degree of randomness is defined, shuffling with a fixed random seed will always produce the same random order for a particular list. The following code snippet demonstrates the usage of shuffling with a specific degree of randomness:
import java.util.*;class Program {public static void main( String args[] ) {List<String> myList = new ArrayList<String>();myList.add("Hippo");myList.add("Panda");myList.add("Brown Bear");myList.add("Koala");myList.add("Polar Bear");myList.add("Elephant");myList.add("Owl");System.out.println("Original list: " + myList);// Randomly shuffle the list with a random number.Collections.shuffle(myList, new Random());System.out.println("List after shuffle with Random(): " + myList);Collections.shuffle(myList, new Random(5));System.out.println("List after shuffle with Random(5): " + myList);}}
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