观察器(Observer)的用法以及其他
1Observable类用于跟踪那些当发生一个改变时希望收到通知的所有个体——无论“状态”是否改变。如果有人说“好了，所有人都要检查自己，并可能要进行更新”，那么Observable类会执行这个任务——为列表中的每个“人”都调用notifyObservers()方法。notifyObservers()方法属于基础类Observable的一部分。2Observable对象会自动调用每个Observer对象的update()方法。
3为真正产生效果，必须从Observable继承，并在衍生类代码的某个地方调用setChanged()。这个方法需要设置“changed”（已改变）标志，它意味着当调用notifyObservers()的时候，所有观察器事实上都会收到通知。
4通过notifyObservers()和update()中的代码的结合，可以应付一些非常复杂的局面。
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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);
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(Graphicsg) {
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;
}
}
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);
Frame f = new BoxObserver(grid);
f.setSize(500, 400);
f.setVisible(true);
f.addWindowListener(
new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
}
}
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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(Graphicsg) {
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;
}
}
原文地址： http://blog.sina.com.cn/s/blog_3f4dc73b01009mls.html
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