观察者模式
因最近在研究PureMVC框架，而该框架的消息通知也就是采用了观察者模式。所以又重新看了一下该设计模式：
首先上源码：
===observer（观察者）参与者
public interface Observer {
public abstract void update(NumberGenerator generator);
}
====subject（目标）参与者
public abstract class NumberGenerator {
private Vector observers = new Vector(); //存储Observer
public void addServer(Observer observer){ //新增Observer
observers.add(observer);
}
public void deleteObserver(Observer observer){ //删除Observer
observers.remove(observer);
}
public void notifyObservers(){ //通知Observer
Iterator it = observers.iterator();
while(it.hasNext()){
Observer o = (Observer)(it.next());
o.update(this);
}
}
public abstract int getNumber(); //取得数值
public abstract void execute(); //产生数值
}
==ConcreteSubject（具体目标）参与者
public class RandomNumberGenerator extends NumberGenerator{
private Random random = new Random();
private int number;
@Override
public void execute() {
for(int i = 0; i < 20; i++){
number = random.nextInt(50);
notifyObservers();
}
}
@Override
public int getNumber() {
return number;
}
}
====ConcreteObserver（具体观察者）参与者
public class DigitObserver implements Observer{
@Override
public void update(NumberGenerator generator) {
System.out.println("DigitObserver: " + generator.getNumber());
try{
Thread.sleep(100);
}catch(InterruptedException e){
e.printStackTrace();
}
}
}
====ConcreteObserver（具体观察者）参与者
public class GraphObserver implements Observer{
@Override
public void update(NumberGenerator generator) {
System.out.println("GraphObserver: ");
int count = generator.getNumber();
for(int i = 0; i < count; i++){
System.out.print("*");
}
System.out.println("");
try{
Thread.sleep(100);
}catch(InterruptedException e){
e.printStackTrace();
}
}
}
public class Main {
/**
* @param args
*/
public static void main(String[] args) {
NumberGenerator generator = new RandomNumberGenerator();
Observer observer1 = new DigitObserver();
Observer observer2 = new GraphObserver();
generator.addServer(observer1);
generator.addServer(observer2);
generator.execute();
}
}
《设计模式： java语言中的应用》对以上代码的解析：
实现java库中的观察者模式：
public class Watched extends Observable {
private String data = "";
public String retrieveData(){
return data;
}
public void chageData(String data){
if(!this.data.equals(data)){
this.data = data;
setChanged();
}
notifyObservers();
}
}
====================================================================
import java.util.Observable;
import java.util.Observer;
public class Watcher implements Observer {
public Watcher(Watched w){
w.addObserver(this);
}
@Override
public void update(Observable o, Object arg) {
System.out.println("Data has been changed to: " + ((Watched)o).retrieveData() + "");
}
}
===================================================================
import java.util.Observer;
public class Tester {
static private Watched watched;
static private Observer watcher;
public static void main(String[] args) {
watched = new Watched();
watcher = new Watcher(watched);
//这里要注意的是改变了四次状态，而只打印了三次，是因为Observable类中有是否变化这一判断
watched.chageData("wo de lao po");
watched.chageData("wo de lao po");
watched.chageData("my wife");
watched.chageData("我的老婆");
}
}