encryption - java caesar cipher code -

i did caesar cipher code java runs doesnt encrypt after user enter key !

here code

public class caesarcipher {     public static final string alphabet = "abcdefghijklmnopqrstuvwxyz";      public static string encrypt(string plaintext, int shiftkey)     {         plaintext = plaintext.tolowercase();         string ciphertext = "";         (int = 0; < plaintext.length(); i++)         {             int charposition = alphabet.indexof(plaintext.charat(i));             int keyval = (shiftkey + charposition) % 26;             char replaceval = alphabet.charat(keyval);             ciphertext += replaceval;         }         return ciphertext;     }      public static string decrypt(string ciphertext, int shiftkey)     {         ciphertext = ciphertext.tolowercase();         string plaintext = "";         (int = 0; < ciphertext.length(); i++)         {             int charposition = alphabet.indexof(ciphertext.charat(i));             int keyval = (charposition - shiftkey) % 26;             if (keyval < 0)             {                 keyval = alphabet.length() + keyval;             }             char replaceval = alphabet.charat(keyval);             plaintext += replaceval;         }         return plaintext;     }      public static void main(string[] args)     {         scanner sc = new scanner(system.in);         system.out.println("enter string encryption: ");         string message = new string();         message = sc.next();         system.out.println(encrypt(message, 3));         system.out.println(decrypt(encrypt(message, 3), 3));         sc.close();     } } 

run:

enter plain text: reem la enter key: 2 cipher text 

using indexof not efficient... can integer arithmetic on char values indices.

i included comments in code explain more, came with.

public class caesarcipher {     // rotate character k-positions     public static char cipher(char c, int k) {         // declare helping constants         final int alphalength = 26;         final char asciishift = character.isuppercase(c) ? 'a' : 'a';         final int ciphershift = k % alphalength;          // shift down 0..25 a..z         char shifted = (char) (c - asciishift);         // rotate letter , handle "wrap-around" negatives , value >= 26         shifted = (char) ((shifted + ciphershift + alphalength) % alphalength);         // shift english characters         return (char) (shifted + asciishift);     }      // rotate string k-positions     public static string cipher(string s, int k) {         stringbuilder sb = new stringbuilder();         (int = 0; < s.length(); i++) {             sb.append(cipher(s.charat(i), k));         }         return sb.tostring();     }      public static void main(string[] args) {         scanner keyboard = new scanner(system.in);         string password;         int key;          system.out.print("please enter password: ");         password = keyboard.nextline();          {             system.out.print("please enter key between 1-25: ");             key = keyboard.nextint();              if (key < 1 || key > 25) {                 system.out.printf(" key must between 1 , 25, entered %d.\n", key);             }         } while (key < 1 || key > 25);           system.out.println("password:\t" + password);         string encryption = cipher(password, key);         system.out.println("encrypted:\t" + encryption);         system.out.println("decrypted:\t" + cipher(encryption, -key));      } } 

the output should

please enter password: abcdefghijklmnopqrstuvwxyz please enter key between 1-25: 1 password:   abcdefghijklmnopqrstuvwxyz encrypted:  bcdefghijklmnopqrstuvwxyza decrypted:  abcdefghijklmnopqrstuvwxyz