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// 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;

}

}