Generate a random code 4 letters long

Hi everyone, I need to generate a 4 letters long code with unique letters for a program of mine. Heres what I have done till now..

Code:

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private String generateLetter() {

                                int n = (int)(Math.random() * 6 + 1);
                                if (n == 1); {
                                        String letter = A;
                                }
                                if (n == 2); {
                                        String letter = B;
                                }
                                if (n == 3); {
                                        String letter = C;
                                }
                                if (n == 4); {
                                        String letter = D;
                                }
                                if (n == 5); {
                                        String letter = E;
                                }
                                if (n == 6); {
                                        String letter = F;
                                }
                                return letter;
                        }


        private String generateSecretCode() {


                String firstLetter = generateLetter();
                String secondLetter = generateLetter();
                String thirdLetter = generateLetter();
                String fourthLetter = generateLetter();

                String secretCode = firstLetter + secondLetter + thirdLetter + fourthLetter;

                return secretCode;
        }

When I try to compile this I get errors like -

C:\A1Stage5\MyProgram.java:11: cannot find symbol
symbol  : variable A
location: class MyProgram
                                        String letter = A;

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I would really appreciate it if any of you could point out the mistake that I am making and advise me on what I should do.

Thanks.

Every variable (String here) that you declare within an if block is visible only within that if block, and is invisible elsewhere in your method. Perhaps it would be best to declare a single String variable letter early in your method and before all the if blocks.

Also, this will never work:

Code:

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String fu = A;

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Far better would be

Code:

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String fu = "A";

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Myself, I'd do it a little differently though. I'd have generateLetter accept a String parameter, say called letters that was a String that held all the possible that could be used to generate a random letter. For instance in your case, you'd pass "ABCDEF" as a parameter.

I'd then use a Random object to generate a random number between 0 and the length of the letters parameter. This index could then be used to get a random char from the letters String via letters.charAt(index), then return this char, or if desired change it to a String before returning it with String.valueOf(...).

Oh my god! how could I forget about that! lol Thanks for pointing that out.
I read the way you said you would do it and it makes sense to do it that way but the thing is that the code is supposed to be generated automatically by the computer so maybe using an array would be a good idea?
This is the code that I wrote using an array but it keeps giving me AAAA as the code :(

Code:

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private String generateSecretCode() {
                String[] letters = {"A", "B", "C", "D", "E", "F"};
                String firstLetter = letters[(int)Math.random() * 6];
                String secondLetter = letters[(int)Math.random() * 6];
                String thirdLetter = letters[(int)Math.random() * 6];
                String fourthLetter = letters[(int)Math.random() * 6];

                String secretCode = firstLetter + secondLetter + thirdLetter + fourthLetter;
                return secretCode;
        }

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I cant seem to understand why it would give me A as the only letter again and again..

What's the difference between this:

Code:

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(int)Math.random() * 6

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and this:

Code:

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(int)(Math.random() * 6)

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?

Quote:

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Originally Posted by Fubarable

What's the difference between this:

Code:

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(int)Math.random() * 6

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and this:

Code:

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(int)(Math.random() * 6)

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?

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ohhh without brackets the (int) gets priority over Math.random * 6. That makes sense.
While I was waiting for your reply, I tried doing it your way and everything seems to be fine and dandy except for this one error that I keep getting..

Code:

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private String generateSecretCode() {
                String validLetters = "ABCDEF";
                char firstLetter = validLetters.charAt((int)(Math.random() * 6));
                char secondLetter = validLetters.charAt((int)(Math.random() * 6));
                char thirdLetter = validLetters.charAt((int)(Math.random() * 6));
                char fourthLetter = validLetters.charAt((int)(Math.random() * 6));

                String secretCode = firstLetter + secondLetter + thirdLetter + fourthLetter;
                return secretCode;
        }

C:\A1Stage5\MyProgram.java:14: incompatible types
found  : int
required: java.lang.String
                String secretCode = firstLetter + secondLetter + thirdLetter + fourthLetter;

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you could build your String with a StringBuilder

StringBuilder? I dont think I am familiar with that term but I will look it up. Though for now my code is working so thanks a lot for helping out :D

One more question. I want all of the four letters to be unique. I looked around on google and people have used the for loop which is something that I dont understand very well right now so is there any other way to ensure that the four letters are unique? maybe by using if or while loops?

Quote:

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I want all of the four letters to be unique.

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Holy creeping requirements Batman!

Seriously though it would be best if you gave all requirements in the first post as this changes things a bit. In this situation I'd use a List here and use Collections.shuffle(myList). But it's getting late for me. Best of luck.

Quote:

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Originally Posted by Fubarable

Holy creeping requirements Batman!

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Haha sorry about that and thanks for all your help man. I really appreciate it :D