Java - Encrypt and Decrypt a file

[Giftx]

Please I need some assistance with a simple code to Enncrypt and Decrypt 26letters of the Alphabet( A to Z) contained in a file called "SecretFile".

Example: File SecretFile contains: ABCDEFGHIJKLMNOPQRSTUVWXYZ.

I really don't know where to start:

so far I have:

import java.??????? // what base class do I import for this operation?
imoport java.io.*;

public class Encryptor implements OutputStream
    {
    private OutputStream mOutput;
    public Encryptor(OutputStream);
    Char Encrypt(char ch)
         {
        if ch > 'A' && ch < 'z')
             {
             int val = (int) ch;
             int Aval = (int)'A';
             val = (val - Aval + 1)%26 Aval;
             return (Char) val;
             }
         }
    } 

class Decryptor exends Encryptor
{
I guess I should do the reverse in the above process???????

Any help will be greatly appreciated.

GiftX.