Generating random License PLate

Question

static String[] checklist = {"FOR", "AXE", "JAM", "JAB", "ZIP", "ARE", "YOU", "JUG", "JAW", "JOY"};
public static void main (String[] args)
{
    int letterRange=26;
    int numberRange=10;

    String  x;
    String letters = new String(Letters(letterRange));
    int numbers = Numbers(numberRange);

    System.out.println(" The randomly generated License Plate is: " +letters + "-" +numbers);
}

public static char[] Letters(int lRange)
{
    char[] letters = new char[3];
    Random r = new Random();
    boolean match = false;
    boolean resultOk = false;
    String result;
    //Generating Random strings (character array)
    for (int x=0; x<letters.length; x++)
    {
        letters[x] = (char)(r.nextInt(26) + 65);
    }

    //Logic for possibility exclusion
    while (true)
    {
        if (match == true)
        {
            for (int x=0; x<letters.length; x++)
            {
                letters[x] = (char)(r.nextInt(26) + 65);
            }
        }
        result = new String(letters);
        for (int i = 0; i < checklist.length; i++)
        {
            if (result == checklist[i])
            {
                match = true;
                break;
            }
            if ((i == checklist.length - 1) && (match == false))
            {
                resultOk = true;
                break;
            }
        }
        if (resultOk == true)
        {
            break;
        }
    }
    return letters;

}

public static int Numbers(int nRange)
{
    int result = 0;
    int[] numbers = new int[3];
    Random r = new Random();
    for (int x = 0; x < numbers.length; x++)
    {
        numbers[x] = r.nextInt(nRange);
    } 
    for (int i = numbers.length; i >= 1; i--)
    {
        result += numbers[i-1] * (10 * (numbers.length - i));
    }
    return result;
}  

Basically I am trying to create a random license plate with three capital letters(65, ASCII code) and with three numbers. When I run the program, I get an exception for static int z=Integer.parseInt(y);. So basically what I did was that I converted String arrays to String, and then String to int and then int to char and after that I did a while loop(saying if letters is not equal to b), then it should work.

Can you please help me? Also, am I supposed to have two methods for this? And I want to surround the license plate by a box to make it look good.

Answer 1

OK, for this time only as you would probably learn more from a good code sample at this point in time than anything else. Please study it and then rewrite it yourself, your teacher won't believe you otherwise and you wouldn't have learned anything.

public class LicensePlate {
    static String[] INVALID_PLATE_LETTERS = { "FOR", "AXE", "JAM", "JAB", "ZIP", "ARE", "YOU",
            "JUG", "JAW", "JOY" };

    static String generateLetters(int amount) {
        String letters = "";
        int n = 'Z' - 'A' + 1;
        for (int i = 0; i < amount; i++) {
            char c = (char) ('A' + Math.random() * n);
            letters += c;
        }
        return letters;
    }

    static String generateDigits(int amount) {
        String digits = "";
        int n = '9' - '0' + 1;
        for (int i = 0; i < amount; i++) {
            char c = (char) ('0' + Math.random() * n);
            digits += c;
        }
        return digits;
    }

    static String generateLicensePlate() {
        String licensePlate;
        String letters;
        do {
            letters = generateLetters(3);
        } while (illegalWord(letters));

        String digits = generateDigits(3);

        licensePlate = letters + "-" + digits;
        return licensePlate;
    }

    private static boolean illegalWord(String letters) {
        for (int i = 0; i < INVALID_PLATE_LETTERS.length; i++) {
            if (letters.equals(INVALID_PLATE_LETTERS[i])) {
                return true;
            }
        }
        return false;
    }

    public static void main(String args[]) {

        System.out.println(generateLicensePlate());
    }
}

Answer 2

Let us start with your array:

static String[] x = {"FOR", "AXE", "JAM", "JAB", "ZIP", "ARE", "YOU", "JUG", "JAW", "JOY"};

It contains the prohibited words. That is good and you don't need anything else than this. No need to create a variable z that contains the array length or a variable b that contains some kind of char from this array.

Now to the main method:

public static void main(String args []) {
    String word;
    do {
        word = generateWord();
    } while(!isAllowed(word)); //generate new words until you've found an allowed one

    // print the generated and allowed word
    System.out.print(" - ");
    // generate 3 digits and print them
    System.out.println();
}

The purpose of this method is to generate you license plate. The assignment mentioned prohibited words (your array x). That means you have to generate the first part of the license plate until you've found a word that is allowed. This task is done in the do/while loop. It generates a 3 character long word and tests if it is allowed. If not, then the loop does another iteration. If "he" found an allowed word, the loop will be exited and your word is stored in the variable word.

The method that generates a 3 character long word looks something like this:

/** Generated a 3 character long word and returns it. */
public static String generateWord() {
    String result = "";
    // generate the word by adding 3 random chars to string "result".
    // You can append a char by doing: result = result + randomChar;
    return result;
}

You already know how to generate such a word, but instead of printing it, you'll need to return that word, so it can be used in the main method. It shouldn't be hard for you to fill this method correctly. The comment contains the "way" to add a generated char to an existing String.

This method:

/**
 * Tests if the given "word" is allowed or not.
 * If the word is in the array "x", then it is not allowed.
 * @return true if the word is allowed
 */
public static boolean isAllowed(String word) {
    /* Create a loop for array "x" that takes every entry of that array
     * and tests if it is the same as "word". If this is the case, then
     * return "false". If the word is not in the array, then this word
     * is allowed. Return "true" in this case.
     */
}

should check if the argument word is part of the array x, which contains the prohibited words. This method needs a loop that will check every single entry of array x. You could either use a for loor:

for (int i = 0; i < x.length; i++) { }

or a for each loop:

for (String entry : x) { }

You can find a lot of information about both loop types and how to use it with an array.

If you have an entry of x, then you need to test if this enty is the same word as the given word string. The class String has a perfect method for this task. Read the JavaDoc and you will find it: JavaDoc of class String.

I hope this guideline helps you achieving your task and I hope you have learned something from it. Good luck :).

Answer 3

This is how I built it for class, straight forward no ...confusion.

public class LicensePlate {
   public static void main(String[] args) {

    // Generate three random uppercase letters
    int letter1 = 65 + (int)(Math.random() * (90 - 65));
    int letter2 = 65 + (int)(Math.random() * (90 - 65));
    int letter3 = 65 + (int)(Math.random() * (90 - 65));    

    // Generate four random digits
    int number1 = (int)(Math.random() * 10);
    int number2 = (int)(Math.random() * 10);
    int number3 = (int)(Math.random() * 10);

    // Display number plate
    System.out.println("" + (char)(letter1) + ((char)(letter2)) + 
        ((char)(letter3)) + "-" + number1 + number2 + number3);
    }
}