Java Cipher Program issue -

i posted program yesterday , i'm stuck. can't figure out why i'm getting errors getting, i've read bunch of stuff, frankly struggling java in general. appreciated...code , errors follow...

/* jursekgregchapter12t.java greg jursek  program encrypt entered text user input  shift value , decrypt text in same manner. */  import java.lang.*;  import java.util.*;  public class jursekgregchapter12t {     public static void main(string[] args)     {     scanner stdin = new scanner(system.in);     string encrypttext; // text encrypted     string decrypttext; // text decrypted     int shiftvalue; // number of spaces shifted via user input       // user enters plain text encryption     system.out.print("please enter text encrypt");     encrypttext = stdin.next();      // user enters shift value     system.out.println("please enter shift value");     shiftvalue = stdin.nextint();      // system prints encrypted text     string encryptedtext = encrypt(encrypttext , shiftvalue); // text has been encrypted     system.out.println(encryptedtext);      // user enters text decryption     system.out.print("please enter text decrypt");     decrypttext = stdin.next();      // user enters shift value     system.out.println("please enter shift value");     shiftvalue = stdin.nextint();      // system prints decrypted text     string decryptedtext = decrypt(decrypttext , shiftvalue); // text has been decrypted     system.out.println(decryptedtext); } // end main           // shift , character manipulation         public static string shift(string enteredtext, int shiftvalue)          {              string convertedtext = "";             for(int = 0; i< enteredtext.length(); i++)             {                 char lowercase = enteredtext.charat(i);                  //convert upper case letters                 char lowercase = character.touppercase(lowercase);                 int charnumber = upperletter;                  //shift letters , wrap text                 int rotateletters = (charnumber + shiftvalue) % 26;                 char shiftletters = (char)rotateshift;                  //populate new string of characters                 convertedtext += shiftletters;             }         return convertedtext;         }          // encryption code         public static string encrypt(string enteredtext, int shiftvalue)         {             string encryptedstring = rotate(enteredtext , shiftvalue);             return encryptedstring;         }          // decryption code         public static string decrypt(string enteredtext, int shiftvalue)         {             int negativeshiftvalue = (-1) * (shiftvalue);             string decryptedstring = rotate(enteredtext , negativeshiftvalue);             return decryptedstring;         }   } //end class jursekgregchapter12t 

errors:

/users/greg/documents/programming/java/jursekgregchapter12t.java:59: error: variable lowercase defined in method shift(string,int)                     char lowercase = character.touppercase(lowercase);                          ^ /users/greg/documents/programming/java/jursekgregchapter12t.java:60: error: cannot find symbol                     int charnumber = upperletter;                                  ^   symbol:   variable upperletter   location: class jursekgregchapter12t /users/greg/documents/programming/java/jursekgregchapter12t.java:64: error: cannot find symbol                     char shiftletters = (char)rotateshift;                                               ^   symbol:   variable rotateshift   location: class jursekgregchapter12t /users/greg/documents/programming/java/jursekgregchapter12t.java:75: error: cannot find symbol                 string encryptedstring = rotate(enteredtext , shiftvalue);                                          ^   symbol:   method rotate(string,int)   location: class jursekgregchapter12t /users/greg/documents/programming/java/jursekgregchapter12t.java:83: error: cannot find symbol                 string decryptedstring = rotate(enteredtext , negativeshiftvalue);                                          ^   symbol:   method rotate(string,int)   location: class jursekgregchapter12t 5 errors [finished in 2.7s exit code 1]