Fisher Yates or Durstenfeld Shuffle in Java

Fisher-Yates shuffle or Knuth shuffle is an algorithm for generating a random shuffle of a finite set. A typical use case would be shuffling the characters in a word or string. A modern efficient variant of Fisher-Yates is known as Durstenfeld algorithm.

The Durstenfeld algorithm is,
    for i from 0 to n − 2 do
        j is a random integer such that i <= j < n
        exchange a[j] and a[i]
    end for

The following Java program demonstrates the use of Durstenfeld algorithm for shuffling characters in a word.

import java.util.concurrent.ThreadLocalRandom;

 * Example Java program to shuffle a word randomly using 
 * modified Fisher-Yates algorithm (Durstenfeld algorithm)
public class ShuffleWord2 {

    public static void main(String[] args) {
        ShuffleWord2 sw = new ShuffleWord2();
        String word = "Superman";
        String shuffled = sw.shuffle(word);
        System.out.println("Original word:"+word);
        System.out.println("Shuffled word:"+shuffled);

     * Shuffles a given word. Uses Fisher-Yates/Durstenfeld algorithm
     * @param word
     * @return 
    private String shuffle(String word) {
        String shuffledWord = word; // start with original
        int wordSize = word.length();
        for(int i=0;i<wordSize-1;i++) {
            int j = ThreadLocalRandom.current().nextInt(i, wordSize);
            shuffledWord = swapCharacters(shuffledWord,j,i);
        return shuffledWord;
     * Swaps characters in a string using the given character positions
     * @param shuffledWord
     * @param position1
     * @param position2
     * @return 
    private String swapCharacters(String shuffledWord, int position1, int position2) {
        char[] charArray = shuffledWord.toCharArray();
        // Replace with a "swap" function, if desired:
        char temp = charArray[position1];
        charArray[position1] = charArray[position2];
        charArray[position2] = temp;
        return new String(charArray);

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