GOLApplet.java

// GOL.java
/*
	Copyright (c) 2006, Toby Oxborrow
	All rights reserved.
	--
	Game of Life
	Runs as a stand alone app or applet.
*/

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

public final class GOLApplet extends JApplet implements Runnable {

	private final int xMax = 50;	// Maximum items across
	private final int yMax = 50;	// Maximum items down

	private boolean[][] curGrid;	// current grid
	private boolean[][] newGrid;	// "current" grid's new state

	Thread runner;

	public void init()
	{
//		System.out.println("init()");

		EmptyGrids();
		PopulateGrid();

		Container contentArea = getContentPane();
		contentArea.setBackground(Color.white);

		BorderLayout layout = new BorderLayout();
		contentArea.setLayout(layout);

		GOLPanel lifeGrid = new GOLPanel();
		contentArea.add(lifeGrid, BorderLayout.CENTER);

		//contentArea.add(textarea, BorderLayout.SOUTH);

		setContentPane(contentArea);
	}


	public void start()
	{
//		System.out.println("start()");
		if (runner == null) runner = new Thread(this);
		runner.start();
	}


	public void run()
	{
//		System.out.println("run()");
		while (runner == Thread.currentThread())
		{
			try { Thread.sleep(1000); }
			catch(InterruptedException e) {}
			Play();
			repaint();
		}
	}


	public void Play()
	{
//		System.out.println("Play()");
		/*
		1. Any live cell with fewer than two neighbours dies, as if by loneliness.
		2. Any live cell with more than three neighbours dies, as if by overcrowding.
		3. Any live cell with two or three neighbours lives, unchanged, to the next generation.
		4. Any dead cell with exactly three neighbours comes to life.
		*/
		for(int y = 0; y < yMax; y++) {
			for(int x = 0; x < xMax; x++) {
				int neighboughs = CountNeighboughs(x, y);
				if(curGrid[x][y] == true) {
					if((neighboughs == 2) || (neighboughs == 3))
						newGrid[x][y] = true;
					else
						newGrid[x][y] = false;
				} else {
					if(neighboughs == 3)
						newGrid[x][y] = true;
					else
						newGrid[x][y] = false;
				}
			}
		}

		// update current grid with new state
		curGrid = newGrid;
	}


	public int CountNeighboughs(int x, int y)
	{
		int n = 0;

		// -- Row above us ---------------------------
		// if we are on the first row, we can skip checking this row
		if(y > 0) {
			// above left
			if(x > 0)
				n += (curGrid[x-1][y-1] == true) ? 1 : 0;
			// above
			n += (curGrid[x][y-1] == true) ? 1 : 0;
			// above right
			if((x + 1) < xMax)
				n += (curGrid[x+1][y-1] == true) ? 1 : 0;
		}

		// -- Our row --------------------------------
		// left
		if(x > 0)
			n += (curGrid[x-1][y] == true) ? 1 : 0;
		// right
		if((x + 1) < xMax)
			n += (curGrid[x+1][y] == true) ? 1 : 0;

		// -- Row below us ---------------------------
		// if we are on the last row, we can skip checking this row
		if((y + 1) < yMax) {
			// below left
			if(x > 0)
				n += (curGrid[x-1][y+1] == true) ? 1 : 0;
			// below
			n += (curGrid[x][y+1] == true) ? 1 : 0;
			// below right
			if((x + 1) < xMax)
				n += (curGrid[x+1][y+1] == true) ? 1 : 0;
		}

		return n;
	}


	public Color GetGridColour(int x, int y)
	{
		return (curGrid[x][y] == true) ? Color.black : Color.white;
	}


	public void SetGridColour(int x, int y, boolean value)
	{
		newGrid[x][y] = value;
	}


	public void EmptyGrids()
	{
		curGrid = new boolean[xMax][yMax];
		newGrid = new boolean[xMax][yMax];

		// create empty grids
		for(int y = 0; y < yMax; y++) {
			for(int x = 0; x < xMax; x++) {
				curGrid[x][y] = false;
				newGrid[x][y] = false;
			}
		}
	}


	// fill "curGrid" with some random values
	public void PopulateGrid()
	{
		Random r = new Random();

		// this effects density
		int dr = r.nextInt(9) + 1;

		// dummy start values
		for(int y = 0; y < yMax; y++) {
			for(int x = 0; x < xMax; x++) {
				if(r.nextInt(10) < dr)
					curGrid[x][y] = true;
			}
		}
	}


	class GOLPanel extends JPanel
	{
		public void paintComponent(Graphics g)
		{
//			System.out.println("paintComponent()");
			Graphics2D g2 = (Graphics2D) g;

			for(int y = 0; y < yMax; y++) {
				for(int x = 0; x < xMax; x++) {
					g2.setPaint(GetGridColour(x, y));
					g2.fill(new Rectangle2D.Double(5 * x, 5 * y, 5, 5));
				}
			}
		}
	}

}