import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.geom.*;

public class ChineseCheckerboard {
    public static void main(String[] args) {
	JFrame frame = new JFrame();
	BoardCanvas canvas = new BoardCanvas(); 
	
	frame.getContentPane().add(canvas);
	frame.setTitle("Chinese checkerboard");
	frame.setSize(400,400);
	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	frame.setVisible(true);
    }
}

class BoardCanvas extends JPanel {
    /*
       We'll have an array, holesInRow, that contains the number of holes per row of the board--
       the first row contains 1 hole, the second 2, the third, 3 (see below).
       We define a utility function drawRow that accepts as its paramter which row to draw
       (as well as the Graphics object sent to paint so we can call our drawing methods).
    */
    public void paintComponent(Graphics g) {
        for(int i = 0; i < holesInRow.length; i++)
            drawRow(g, i);
    }

    /*
       drawRow figures out the (horizontal) center of the display, the width of the current row (from the number
       of holes in that row, their size and the spacing gap). It then calculates the starting horizintal position
       by subtracting half of the row width from the center position, so that half of the row will be displayed on
       one side, and the other half on the other. The vertical position remains fixed for the entire row.
    */
    void drawRow(Graphics g, int row) {
	Graphics2D g2 = (Graphics2D) g;
        int centerX = getWidth() / 2;           // figure out center of display
        int startY = 20;
        int numHoles = holesInRow[row];
        int rowWidth = numHoles * holeDiam + (numHoles-1) * holeGap;    //row width is number of holes + appropriate number of spacings
        int startX = centerX - rowWidth / 2;            // Starting horizontal position is centerX less half the row width
        int y = startY + row * (holeDiam + holeGap);    // Vertically position based upon which row you're displaying
        g2.setPaint(Color.RED);
        for (int i = 0; i < numHoles; i++) {            // Draw each hole
	    Ellipse2D oval = new Ellipse2D.Double(startX + i * (holeDiam + holeGap), y, holeDiam, holeDiam);
            g2.fill(oval);
            g2.draw(oval);
        }
    }

    final int holeDiam = 15;
    final int holeGap = (int)(holeDiam * 0.25);

    // Here's the array containing the number of holes per row

    int [] holesInRow = {1, 2, 3, 4, 13, 12, 11, 10, 9, 10, 11, 12, 13, 4, 3, 2, 1};
}