I have implemented Conway's Game of Life simulation. What can I improve? How could I structure my programme better? All suggestions would be appreciated.

World.java:

public class World {

private int WORLDSIZE;
private final int DEAD = 0;
private final int ALIVE = 1;
private int world[][];
private int worldCopy[][];

public World(int WORLDSIZE) {
    this.WORLDSIZE = WORLDSIZE;
    this.world = new int[WORLDSIZE][WORLDSIZE];
    this.worldCopy = new int[WORLDSIZE][WORLDSIZE];
}

public int getWorldSize() {
    return this.WORLDSIZE;
}

public int[][] getWorld() {
    return this.world;
}

public int getCellState(int x, int y) {

    if (world[x][y] == ALIVE)
        return ALIVE;
    else
        return DEAD;
}

public int getAlive() {
    return this.ALIVE;
}

public int getNeighborCells(int x, int y) {

    int neighbors = 0;

    for (int i = x - 1; i <= x + 1; i++) {
        for (int j = y - 1; j <= y + 1; j++) {

            if (world[i][j] == ALIVE && (x != i || y != j))
                neighbors += 1;
        }
    }

    return neighbors;
}

public void createRandomWorld() {

    for (int y = 0; y < WORLDSIZE; y++) {
        for (int x = 0; x < WORLDSIZE; x++) {

            if (Math.random() > 0.9) {
                world[x][y] = ALIVE;
            } else
                world[x][y] = DEAD;
        }
    }
}

public int[][] applyRules() {

    for (int i = 1; i < WORLDSIZE - 1; i++) {
        for (int j = 1; j < WORLDSIZE - 1; j++) {

            int neighbors = getNeighborCells(i, j);

            if (world[i][j] == ALIVE) { // zur Zeit t lebendig

                if ((neighbors < 2) || (neighbors > 3)) {
                    worldCopy[i][j] = DEAD; // Zelle tot
                }

                if (neighbors == 2 || neighbors == 3) {
                    worldCopy[i][j] = ALIVE;
                }
            }

            if (world[i][j] == 0 && neighbors == 3) { // zur Zeit t tot
                worldCopy[i][j] = ALIVE;
            }
        }

    }

    return worldCopy;
}

public void updateWorld() {
    world = applyRules();
}

Board.java:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics; 
import javax.swing.JPanel;

public class Board extends JPanel {

private int width = 250;
private int height = 250;
private World world;
private final int CELLSIZE = 5;

public Board(World world) {
    this.world = world;
    world.createRandomWorld();      
    setPreferredSize(new Dimension(width, height));
    setBackground(Color.YELLOW);
}

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);

    for (int i = 0; i < world.getWorldSize(); i++) {
        for (int j = 0; j < world.getWorldSize(); j++) {

            if (world.getCellState(i, j) == world.getAlive()) {
                g.setColor(Color.RED);
                g.fillRect(i * CELLSIZE, j * CELLSIZE, CELLSIZE, CELLSIZE);
            }

            else {
                g.setColor(Color.YELLOW);
                g.fillRect(i * CELLSIZE, j * CELLSIZE, CELLSIZE, CELLSIZE);
            }
        }
    }
  }
}

Simulation.java:

import java.util.Timer;
import java.util.TimerTask;

public class Simulation {

private World world;
private Board board;
private Timer timer = new Timer();
private final int period = 100;

public Simulation(Board board, World world) {
    this.board = board;
    this.world = world;
    this.simulate();
}

public void simulate() {
    timer.schedule(new TimerTask() {

        @Override
        public void run() {

            world.applyRules();
            world.updateWorld();

            board.repaint();
        }

    }, 0, period);
 }
}

Main.java:

import javax.swing.JFrame;

public class Main {

private World world;
private Board board;
private Simulation simulation;
private JFrame frame = new JFrame("GameOfLife");
private final int width = 250, height = 250;

public Main() {
    world = new World(50);
    board = new Board(world);
    simulation = new Simulation(board, world);

    frame.setSize(width, height);
    frame.add(board);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    frame.setVisible(true);
}

public static void main(String[] args) {

    new Main();
 }
}

Thank you in advance.