//: BoxObserver.java
//////////////////////////////////////////////////
// Copyright (c) Bruce Eckel, 1998
// Source code file from the book "Thinking in Java"
// All rights reserved EXCEPT as allowed by the
// following statements: You can freely use this file
// for your own work (personal or commercial),
// including modifications and distribution in
// executable form only. Permission is granted to use
// this file in classroom situations, including its
// use in presentation materials, as long as the book
// "Thinking in Java" is cited as the source.
// Except in classroom situations, you cannot copy
// and distribute this code; instead, the sole
// distribution point is http://www.BruceEckel.com
// (and official mirror sites) where it is
// freely available. You cannot remove this
// copyright and notice. You cannot distribute
// modified versions of the source code in this
// package. You cannot use this file in printed
// media without the express permission of the
// author. Bruce Eckel makes no representation about
// the suitability of this software for any purpose.
// It is provided "as is" without express or implied
// warranty of any kind, including any implied
// warranty of merchantability, fitness for a
// particular purpose or non-infringement. The entire
// risk as to the quality and performance of the
// software is with you. Bruce Eckel and the
// publisher shall not be liable for any damages
// suffered by you or any third party as a result of
// using or distributing software. In no event will
// Bruce Eckel or the publisher be liable for any
// lost revenue, profit, or data, or for direct,
// indirect, special, consequential, incidental, or
// punitive damages, however caused and regardless of
// the theory of liability, arising out of the use of
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// and the publisher have been advised of the
// possibility of such damages. Should the software
// prove defective, you assume the cost of all
// necessary servicing, repair, or correction. If you
// think you've found an error, please email all
// modified files with clearly commented changes to:
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// address for non-code errors found in the book.)
/////////////////////////////////////////////////
// Demonstration of Observer pattern using
// Java's built-in observer classes.
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 Frame {
Observable notifier = new BoxObservable();
public BoxObserver(int grid) {
setTitle("Demonstrates Observer pattern");
setLayout(new GridLayout(grid, grid));
for(int x = 0; x < grid; x++)
for(int y = 0; y < grid; y++)
add(new OCBox(x, y, notifier));
}
public static void main(String[] args) {
int grid = 8;
if(args.length > 0)
grid = Integer.parseInt(args[0]);
Frame f = new BoxObserver(grid);
f.setSize(500, 400);
f.setVisible(true);
f.addWindowListener(
new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
}
}
class OCBox extends Canvas 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 final 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(new ML());
}
public void paint(Graphics 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;
}
} ///:~ |