Art And Science of Java Chapter 3 Exercise 10

My small program draws a pattern for Tic Tac Toe game. Thanks for watching!
--------------------------------------------------------------------------------------------------------------------------
/* File:TicTacToeBoard.java
 *
 * Programs draws a figure necessary to play TicTacToe
 *
 */

import acm.program.*;
import acm.graphics.*;

public class TicTacTocBoard extends GraphicsProgram {
  public void run() {

/* x and y coordinates of window centre */
int midX = getWidth() / 2;
int midY = getHeight() / 2;

/* useful calculation for reference points */
double thirdOfBoard = 0.166 * BOARD_SIZE;
double halfOfBoard = 0.5 * BOARD_SIZE;


GLine horizontalTopLine = new GLine(midX-halfOfBoard, midY-thirdOfBoard, midX+halfOfBoard, midY-thirdOfBoard);
GLine horizontalBottomLine = new GLine(midX-halfOfBoard, midY+thirdOfBoard, midX+halfOfBoard, midY+thirdOfBoard);

GLine verticalLeftLine = new GLine(midX-thirdOfBoard, midY-halfOfBoard, midX-thirdOfBoard, midY+halfOfBoard);
GLine verticalRightLine = new GLine(midX+thirdOfBoard, midY-halfOfBoard, midX+thirdOfBoard, midY+halfOfBoard);

add(horizontalTopLine);
add(horizontalBottomLine);
add(verticalLeftLine);
add(verticalRightLine);

}

private static final int BOARD_SIZE = 100;

}

--------------------------------------------------------------------------------------------------------------------------