How to use the Collections.shuffle method in Java
Educative Answers TeamThe 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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