《Head First Design Pattern》一书中对观察者模式的定义如下:
The Observer Pattern defines a one-to-many dependency objects so that when one object changes state, all of its dependents are notified and updated automatically.
观察者设计模式定义了对象间的一种一对多的依赖关系,以便一个对象的状态发生变化时,所有依赖于它的对象都得到通知并自动刷新,
观察者模式
。从根本上说,该模式必须包含两个角色:观察者和被观察对象。下面是设计模式中包含角色的UML类图(来自百度百科)。
观察者<喎?http://www.2cto.com/kf/ware/vc/" target="_blank" class="keylink">vc3Ryb25nPqOoT2JzZXJ2ZXKjqb2r19S8uteisuG1vbG7uduy7LbUz/OjqFN1YmplY3SjqdbQo6yxu7nbsuy21M/zvau527Ls1d+05rfF1NrSu7j2yN3G96OoQ29udGFpbmVyo6nA76GjPGJyIC8+DQo8c3Ryb25nPrG7uduy7Dwvc3Ryb25nPrbUz/OjqFN1YmplY3SjqbeiyfrBy8Sz1tax5Luvo6y008jdxvfW0LXDtb3L+dPQ16Ky4bn9tcS527Ls1d+jrL2rseS7r82o1qq527Ls1d+hozwvcD4NCjxwPs/Cw+a+2dXi0fnSu7j2wP3X06O6scjI59K7uPbQodPOz7ejrEHLtbP20ru49squvfjWxrXEyv2jrELLtbP2xuS21NOmtcS2/r341sa94bn7o6xDy7Wz9sbkttTTprXEsMu9+NbGveG5+6OsRMu1s/bG5LbU06a1xMquwfm9+NbGveG5+6GjPGJyIC8+DQrKudPDuduy7NXfxKPKvUG/ydLU1/fOqrG7uduy7NXfo6hTdWJqZWN0o6mjrEKhokOhokS/ydLU1/fOqrnbsuzV36OoT2JzZXJ2ZXKjqaGjPC9wPg0KPHA+z8LD5srHSmF2YbT6wuvKvsD9o7o8YnIgLz4NCjxzdHJvbmc+uduy7NXfvdO/2qO6PC9zdHJvbmc+PC9wPg0KPHByZSBjbGFzcz0="brush:java;">public interface IObserver { public void update();}
被观察者接口:
<code class="hljs cs">public interface ISubject { public void addObserver(IObserver o); public void deleteObserver(IObserver o); public void notifyObservers();}</code>
实体被观察者A:就是游戏中的A
<code class="hljs java">public class Number implements ISubject { private List<iobserver>observers; private int number; public Number() { bservers = new ArrayList<iobserver>(); } public void setNumber(int number) { this.number = number; notifyObservers(); } public int getNumber() { return number; } @Override public void addObserver(IObserver o) { observers.add(o); } @Override public void deleteObserver(IObserver o) { observers.remove(o); } @Override public void notifyObservers() { for (IObserver observer : observers) { observer.update(); } }}</iobserver></iobserver></code>
实体观察者B:游戏中的B,将A给的数字转成二进制
<code class="hljs java">public class BinTranslator implements IObserver { private ISubject subject; public BinTranslator(Number number) { subject = number; subject.addObserver(this); } @Override public void update() { if (subject instanceof Number) { Number number = (Number) subject; int inum = number.getNumber(); System.out.println(inum + "=" + Integer.toBinaryString(inum)); } }}</code>
实体观察者D:游戏中的D,将A给的数字转成十六进制
<code class="hljs java">public class HexTranslator implements IObserver { private ISubject subject; public HexTranslator(Number number) { subject = number; subject.addObserver(this); } @Override public void update() { if (subject instanceof Number) { Number number = (Number) subject; int inum = number.getNumber(); System.out.println(inum + "=0x" + Integer.toHexString(inum)); } }}</code>
观察者模式测试代码:我们开始做游戏了
<code class="hljs cs">public class ObserverPattern { @SuppressWarnings("unused") public static void main(String[] args) { Number number = new Number(); IObserver bin = new BinTranslator(number); IObserver hex = new HexTranslator(number); number.setNumber(12); number.setNumber(-1); }}</code>
运行结果:
<code class="hljs ini">12=110012=0xc-1=11111111111111111111111111111111-1=0xffffffff</code>
其实Java JDK本身提供了设计模式等额实现:
java.util.Observer是一个接口,观察者接口,相当于我们上面的IObserver接口,
电脑资料
《观察者模式》(https://www.unjs.com)。我们需要实现一个观察者的时候只需要实现这个接口就OK了。java.util.Observable是一个类,被观察者类,我们需要实现一个被观察者的时候只需要继承这个类就OK了。