Game of live

World.java

package gol;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class World {

	Set<String> world = new HashSet<String>();

	public void addLiveCell(int x, int y) {
		world.add(getkey(x, y));
	}

	private String getkey(int x, int y) {
		return x + ":" + y;
	}
	
	private int getX(String key) {
		return Integer.valueOf(key.split(":")[0]);
	}
	
	private int getY(String key) {
		return Integer.valueOf(key.split(":")[1]);
	}

	public int getNumberOfNeighbour(int x, int y) {
		int numberOfNb = 0;
		List<String> neighbour = getNeighbour(x,y);
		for (String key : neighbour) {
			if (world.contains(key)) {
				numberOfNb++;
			}
		}
		
		return numberOfNb;
	}
	
	public int getNumberOfNeighbour(String key) {
		return getNumberOfNeighbour(getX(key), getY(key));
	}

	
	private List<String> getNeighbour(String key) {
		return getNeighbour(getX(key), getY(key));
	}

	private java.util.List<String> getNeighbour(int x, int y) {
		List<String> nb = new ArrayList<String>();
		nb.add(getkey(x-1, y-1));
		nb.add(getkey(x-1, y));
		nb.add(getkey(x-1, y+1));
		nb.add(getkey(x, y-1));
		nb.add(getkey(x, y+1));
		nb.add(getkey(x+1, y-1));
		nb.add(getkey(x+1, y));
		nb.add(getkey(x+1, y+1));
		return nb;
	}

	public void tick() {
		Set<String> newWorld = new HashSet<String>();
		Set<String> neighbourCells = new HashSet<String>();
		for(String key : world) {
			if (ifThreeOrTwoNeighbour(key)) {
				newWorld.add(key);
			}
			neighbourCells.addAll(getNeighbour(key));
		}

		for(String key : neighbourCells) {
			if (ifThreeNeighbour(key)) {
				newWorld.add(key);
			}
		}
		
		world = newWorld;
		
	}

	private boolean ifThreeOrTwoNeighbour(String key) {
		int numberOfNeighbour = getNumberOfNeighbour(key);
		return numberOfNeighbour == 3 || numberOfNeighbour == 2;
	}
	
	private boolean ifThreeNeighbour(String key) {
		int numberOfNeighbour = getNumberOfNeighbour(key);
		return numberOfNeighbour == 3;
	}

	public boolean isAlive(int x, int y) {
		return world.contains(getkey(x, y));
	}

}