Chess960 initial position generator in Java

Chess960.java

public class Chess960 {
    public static void main(String[] args) {
        char[] board = new char[8];

        for (int i = 0; i < 2; i++) {
            int r = (int) (Math.random() * 4) * 2;

            if (i == 1) {
                r++;
            }

            board[r] = 'B';
        }

        char[] queenKnights = {'Q', 'N', 'N'};
        for (int i = 0; i < queenKnights.length; i++) {
            int index = (int) (Math.random() * (6 - i));

            while (board[index] != 0) {
                index++;
            }

            board[index] = queenKnights[i];
        }

        char[] kingRooks = {'R', 'K', 'R'};
        int index = 0;
        for (int i = 0; i < kingRooks.length; i++) {
            while (board[index] != 0) {
                index++;
            }

            board[index] = kingRooks[i];
            index++;
        }

        for (int i = 0; i < board.length; i++) {
            System.out.print(board[i] + " ");
        }

        System.out.println();
    }
}