public int strStr(String haystack, String needle) {

         if(haystack == null || needle == null)

         {

             return -1;

         }

         for (int i = 0; i <= (haystack.length()-needle.length()); i++)

         {

             int m = i;

             for (int j = 0; j < needle.length(); j++)

             {

                 if (needle.charAt(j) == haystack.charAt(m))

                 {

                     m++;

                     if((m-i) == needle.length())

                     {

                         return i;

                     }

                 }

                 else

                 {

                     break;

                 }

             }

         }

         return -1;

     }