Java code to print permutation of a String. Impl is based on logic described here - http://www.ardendertat.com/2011/10/28/programming-interview-questions-11-all-permutations-of-string/

gistfile1.java

import java.util.List;
import java.util.ArrayList;

public class Test {

     public static void main(String []args)
     {
        List<String> output = permut("ABC"); 
        
        System.out.println("===== Output =====");
        
        for (String str : output) 
        {
            System.out.println(str);
        }    
     }
     
     // permutOf("ABC") = madInsert(A, permutOf("BC")) 
     private static List<String> permut(String str) 
     {
         System.out.println("Finding permutation of "+str);
         
         List<String> perms = new ArrayList<String>();
         
         // Permutation of "A" is "A" itself.
         if (str.length() == 1) 
         {
             perms.add(str);
             
             return perms;
         }

         // Keep the Nth char aside. Keep aside "A" from "ABC"
         String firstChar = str.substring(0,1);
         
         // Find permutation of N-1 chars. To find permute of "ABC", find permute of "BC".
         List<String> nMinusOnePermsOutput = permut(str.substring(1));
         
         // Insert Nth Char into all positions of N-1 Permutation O/P. Insert "A" into permuteOf("BC")
         perms = madInsert(firstChar, nMinusOnePermsOutput);
         
         return perms;
     }
     
     // This method iterates over each item in the N-1 o/p and inserts Nth char into it.
     private static List<String> madInsert(String firstChar, List<String> nMinusOnePermsOutput)     
     {
         
         List<String> outputList = new ArrayList<String>();
         
         for (String str : nMinusOnePermsOutput) {
             outputList.addAll(insertChar(str, firstChar));
         }
         
         return outputList;
     }
     
     // Insert Nth char into all possible locations of current string.
     // For eg:- for inputs char 'A' and String "BC", o/p will be "ABC", "BAC" and "BCA".
     private static List<String> insertChar(String str, String firstChar) 
     {
         System.out.println("Inserting "+ firstChar + " into " + str);
         
         List<String> outputList = new ArrayList<String>();
         
         for (int i=0;i<=str.length();i++) 
         {
           StringBuffer sb = new StringBuffer(str);
           sb.insert(i, firstChar);
           outputList.add(sb.toString());
         }
         
         return outputList;
     }
}