java - Creating a multicolored board -

i create multicolored board, starting first square black, blue, red, , yellow, squares being filled diagonally , there no empty colored squares. know algorithm wrong, have not clue how fix it. currently, code prints out this

import javax.swing.jframe; import javax.swing.jpanel; import java.awt.color; import java.awt.dimension; import java.awt.graphics; import java.awt.graphics2d; import java.awt.insets;  public class grid extends jpanel { private static final long serialversionuid = 1l; public static final int grid_count = 8; private color[] colors = { color.black, color.yellow, color.red,         color.blue }; private int colorindex = 0;  public void paintcomponent(graphics g) {     super.paintcomponent(g);     graphics2d graphics = (graphics2d) g;     graphics.setcolor(color.black);      dimension size = getsize();     insets insets = getinsets();     int w = size.width - insets.left - insets.right;     int h = size.height - insets.top - insets.bottom;      int sqrwidth = (int)((double)w / grid_count);     int sqrheight = (int)((double)h / grid_count);     (int row = 0; row < grid_count; row++) {         (int col = 0; col < grid_count; col++) {                 int x = (int) (row * (double) w / grid_count);                 int y = (int) (col * (double) h / grid_count);                 if ((row + col) % 2 == 0) {                     int colorindex = (row + col) % 4;                     graphics.fillrect(x, y, sqrwidth, sqrheight);                     graphics.setcolor(colors[colorindex]);                     colorindex = (colorindex + 1) % colors.length;     }  }  public static void main(string[] args) {     grid grid = new grid();     grid.setpreferredsize(new dimension(400, 400));     jframe frame = new jframe("grid");     frame.setdefaultcloseoperation(jframe.exit_on_close);     frame.add(grid);     frame.pack();     frame.setlocationrelativeto(null);     frame.setvisible(true);  } 

}

let's @ pattern:

bk gr pn bl gr pn bl bk pn bl bk gr bl bk gr pn 

but make simpler, let's call bk 0, gr 1, pn 2 , bl 3 get:

0 1 2 3 1 2 3 0 2 3 0 1 3 0 1 2 

this pattern produced calculating tile[x][y] = (x + y) % 4 every tile, , using lookup table convert these numbers colours (either use enumeration, or instead of assigning integer value tile use integer look-up in table of colours , assign colour tile)

if you've never seen before, % 4 means 'divide 4 , return remainder of division'.