How do i stop repeating numbers?

Question

I have to print a bingo board which goes from 1-15,16-30 and so on. I have the board printed out but I keep getting repeating numbers. In my display method I can't seem to pinpoint why the if statement for repeating numbers doesn't work. I'm also new to this website but if there's some unclear points I will respond to them.

public class BingoArraysAssignment {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

        int[][] board1 = new int[5][5];
        int[][] board2 = new int[5][5];
        int[][] board3 = new int[5][5];

        display(board1);
        //display2(board3);
        //display(board2);

    }

    public static void display(int[][] board1) {
        //int[][] board1 = new int[5][5];
        int z = 1, v = 15, y, counter = 0;

        for (int i = 0; i <= 4; i++) {

            for (int j = 0; j <= 4; j++) {
                //counter++;


                y = (int) (Math.random() * v + z);
                if (board1[i][j] == y) {
                    j--;
                    set(board1[i][j], 0);        

                }
                if (board1[i][j] == 0) {

                    board1[i][j] = y;
                    System.out.print("|" + board1[i][j]);
                    //break;

                }

            }
            z = z + 15;
            v = v + 15;

            System.out.println("  ");
        }

    }
}

Answer 1

random number can repeat. You must create a random sequence of 25 numbers and use it:

List<Integer> numbers = new List();
list.add(...);

Collections.shuffle(numbers);
Iterrator<Integer> numberItr = list.iterrator();


 .....
 y = numberItr.next();

Answer 2

Don't use Math.Random() , do what Bingo does in real life. Create a list with all the numbers needed, and extract one number randomly from the list.

Next time you extract from it, you won't get the same value.

Answer 3

Create a list containing the numbers 1 to 75. Randomly select 5 from 1-15, 5 from 16-30 and so on... Then remove the numbers you selected from the list. This way you won't get any number twice.

Here's an example

 //array need numbers from 1 to 15(Can be populated with a loop)
    int[] colm = { 1, 2, 3, 4, 5, 14, 15}; //Enter 1 to 15
    int[] colm2 = {16,17,18,19,20,21,22,30};//...16 to 30
    int[][] board = new int[5][5];
 //...
    List l = new ArrayList();
    for(int i: colm)
        l.add(i);

    Collections.shuffle(l);

    for (int i = 0; i < 5; i++)
       for (int j = 0; j < 5; j++)
      if(i=0) board[i][j] = colm1[j]
      if(i=1) board[i][j] = colm2[j]
    //...

        }
     }