// patterns/BoxObserver.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Demonstration of Observer pattern using
// Java's built-in observer classes
// {ExcludeFromTravisCI}
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import onjava.*;
import onjava.MouseClick;

// You must inherit a new type of Observable:
class BoxObservable extends Observable {
 @Override
 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) {
 new TimedAbort(4);
 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(DISPOSE_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.darkGray, Color.gray, Color.green,
 Color.lightGray, Color.magenta,
 Color.orange, Color.pink, Color.red,
 Color.white, Color.yellow
 };
 static Color newColor() {
 return COLORS[
 (int)(Math.random() * COLORS.length)
 ];
 }
 OCBox(int x, int y, Observable notifier) {
 this.x = x;
 this.y = y;
 notifier.addObserver(this);
 this.notifier = notifier;
 addMouseListener((MouseClick)
 e -> notifier.notifyObservers(OCBox.this));
 }
 @Override
 public void paintComponent(Graphics g) {
 super.paintComponent(g);
 g.setColor(cColor);
 Dimension s = getSize();
 g.fillRect(0, 0, s.width, s.height);
 }
 @Override
 public void update(Observable o, Object arg) {
 OCBox clicked = (OCBox)arg;
 if(nextTo(clicked)) {
 cColor = clicked.cColor;
 repaint();
 }
 }
 private boolean nextTo(OCBox b) {
 return Math.abs(x - b.x) <= 1 &&
 Math.abs(y - b.y) <= 1;
 }
}