Rearranger.java

import java.util.Scanner;

public class Rearranger {

   /**
   *    Program:    Rearranger.java
   *    Purpose:    Re-arrange the letters of a word (up to 10 letters) every possible way.
   *    Creator:    Chris Clarke
   *    Created:    20.07.2015
   */

   private static int c = 0;        // counts the number of different variations
   private static String[] theArray;    // for displaying each string permutation

   public static void main(String[] args) {

      final int MAX = 10; // maximum length of string
      Scanner scan = new Scanner(System.in); // reads keyboard input
      String s = null;

      // example: s = "0123456789"

      // assign to s the command line argument, if any
      if (args.length>0) {
         s = args[0];
      } else {
         // prompt user for input
         System.out.print("Enter a string (up to "+MAX+" characters long): ");
         // assign to s the String entered by the user
         s = scan.next();
      }//if

      // to avoid excessive runtime/memory usage
      if (s.length()>MAX) {
         System.out.println("String too long! Max "+MAX+" characters.");
         return; // exit program
      }//if

      // no. of permutations is factorial of string length
      theArray = new String[factorial(s.length())];

      // method call to display each permutation
      displayString(s);
      System.out.println("\nThere are "+c+" permutations/re-arrangements of \""+s+"\".");
   }//main()

   public static void displayString(String s) {
      displayString("", s);
   }//displayString(String)

   private static void displayString(String prefix, String s) {
      int n = s.length();
      if (n == 0) {
         // print solution
         System.out.print(prefix+"\t");
         theArray[c++] = prefix;
      } else {
         for (int i=0; i<n; i++) {
            // recursive method call
            displayString(prefix+s.charAt(i), s.substring(0, i)+s.substring(i+1, n));
         }//for
      }//if
   }//displayString(String, String)

   public static int factorial(int n) {
      return (n == 1)? 1: n * factorial(n - 1);
   }//factorial()
}//class Rearranger