Thread: Help With Java Encryption Program

Right, i am in dire need of help, I have been given a java assignment to do where I need to write code which first reads in a line of text from the keyboard, displays that line, encrypts it, displays the encrypted text, decrypts the encrypted text and finally displays the decrypted text (which should look like the original).

Its to be made as an expansion of the following code:
This is the first Class (Caeser)

/** Class for doing encryption and decryption using the Caesar Cipher. */
public class Caeser {
public static final int ALPHASIZE = 26; // English alphabet(uppercase)
public static final char[] alpha =
{'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P',
'Q','R','S','T','U','V','W','X','Y','Z'};
 
protected char[] encrypt = new char[ALPHASIZE]; // Encryption array
protected char[] decrypt = new char[ALPHASIZE]; // Decryption array
/** Constructor that initializes the encryption and decryption arrays */
public Caeser() {
for (int i=0; i<ALPHASIZE; i++)
encrypt[i] = alpha[(i + 3) % ALPHASIZE]; // rotate by 3 places
for (int i=0; i<ALPHASIZE; i++)
decrypt[encrypt[i] - 'A'] = alpha[i]; // reverse of encrypt
}
/** Encryption method */
public String encrypt(String secret) {
char[] mess = secret.toCharArray(); // the message array
for (int i=0; i<mess.length; i++) // encryption loop
if (Character.isUpperCase(mess[i])) // we have a letter to change
mess[i] = encrypt[mess[i] - 'A']; // encrypt letter
return new String(mess);
}
/** Decryption method */
public String decrypt(String secret) {
char[] mess = secret.toCharArray(); // the message array
for (int i=0; i<mess.length; i++) // decryption loop
if (Character.isUpperCase(mess[i])) // we have a letter to change
mess[i] = decrypt[mess[i] - 'A']; // decrypt letter
return new String(mess);
}
}
/** Simple class for testing the Caesar cipher */

This is the second class - CaeserTryOut

public class CaeserTryOut {
public static void main(String[] args) {
Caeser cipher = new Caeser(); // Create a Caesar cipher object
String secret = "THE EAGLE IS IN PLAY; MEET AT JOE'S.";
secret = cipher.encrypt(secret);
System.out.println(secret); // the cipher text
secret = cipher.decrypt(secret);
System.out.println(secret); // should be original again
}
}

But I am so rusty with java as i have not used it in a while that I have no idea where to go from this...All i know is that I need to generate a random replacement for each character :S

"The encryption should involve generating a random replacement for each character (both upper and lower case), while ensuring that the same character appearing more than once in the original is replaced by the same character in the coded string. You must also ensure that no two characters in the original are coded as the same character in the coded string, in order to enable successful decryption. Non-alphabetic characters in the original should remain as they are in the coded string. The code should include instance methods to encrypt and decrypt, both taking a string passed as parameter.
Both upper and lower-case characters should be encrypted and characters in the decrypted message should match the case of those in the original message."

Even is someone can just point me in the right direction, Thanks!