AllPermutationsOfAString.java

/**
  * Java program to find all the permutations of a given String using recursion. 
  * For example, given a String "XYZ", this program will print 
  * all 6 possible permutations of
  * input e.g. XYZ, XZY, YXZ, YZX, ZXY, XYX
  *
  * @author Javin Paul
  */
public class AllPermutationsOfAString {

    public static void main(String args[]) {
        permutation("123");
    }

   
 /*
  * A method exposed to client to calculate permutation of String in Java. 
  */
   public static void permutation(String input){
          permutation("", input);
   }

   /*
    * Recursive method which actually prints all permutations
    * of given String, but since we are passing an empty String
    * as current permutation to start with,
    * I have made this method private and didn't expose it to client.
    */
   private static void permutation(String perm, String word) {
        if (word.isEmpty()) {
            System.err.println(perm + word);
        } else {
            for (int i = 0; i < word.length(); i++) {
                permutation(perm + word.charAt(i), word.substring(0, i) 
                                + word.substring(i + 1, word.length()));
            }
        }

    }
}