boxobserver.java

thinking in patterns

//: observer:BoxObserver.java
// Demonstration of Observer pattern using
// Java's built-in observer classes.
package observer;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

// You must inherit a new type of Observable:
class BoxObservable extends Observable {
  public void notifyObservers(Object b) {
    // Otherwise it won't propagate changes:
    setChanged();
    super.notifyObservers(b);
  }
}

public class BoxObserver extends JFrame {
  Observable notifier = new BoxObservable();
  public BoxObserver(int grid) {
    setTitle("Demonstrates Observer pattern");
    Container cp = getContentPane();
    cp.setLayout(new GridLayout(grid, grid));
    for(int x = 0; x < grid; x++)
      for(int y = 0; y < grid; y++)
        cp.add(new OCBox(x, y, notifier));
  }   
  public static void main(String[] args) {
    int grid = 8;
    if(args.length > 0)
      grid = Integer.parseInt(args[0]);
    JFrame f = new BoxObserver(grid);
    f.setSize(500, 400);
    f.setVisible(true);
    f.setDefaultCloseOperation(EXIT_ON_CLOSE);
  }
}

class OCBox extends JPanel implements Observer {
  Observable notifier;
  int x, y; // Locations in grid
  Color cColor = newColor();
  static final Color[] colors = { 
    Color.BLACK, Color.BLUE, Color.CYAN, 
    Color.DARK_GRAY, Color.GRAY, Color.GREEN,
    Color.LIGHT_GRAY, Color.MAGENTA, 
    Color.ORANGE, Color.PINK, Color.RED, 
    Color.WHITE, Color.YELLOW 
  };
  static Random rand = new Random();
  static final Color newColor() {
    return colors[rand.nextInt(colors.length)];
  }
  OCBox(int x, int y, Observable notifier) {
    this.x = x;
    this.y = y;
    notifier.addObserver(this);
    this.notifier = notifier;
    addMouseListener(new ML());
  }
  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.setColor(cColor);
    Dimension s = getSize();
    g.fillRect(0, 0, s.width, s.height);
  }
  class ML extends MouseAdapter {
    public void mousePressed(MouseEvent e) {
      notifier.notifyObservers(OCBox.this);
    }
  }
  public void update(Observable o, Object arg) {
    OCBox clicked = (OCBox)arg;
    if(nextTo(clicked)) {
      cColor = clicked.cColor;
      repaint();
    }
  }
  private final boolean nextTo(OCBox b) {
    return Math.abs(x - b.x) <= 1 && 
           Math.abs(y - b.y) <= 1;
  }
} ///:~