import java.util.Iterator;
import java.util.Vector;
/**
*
* @author Seastar
*/
interface Observed {
public void addObserver(Observer o);
public void removeObserver(Observer o);
public void update();
}
interface Observer {
public void takeAction();
}
class Invoker {
private Observer o;
Handler handler;
public Invoker(Observer o) {
new Handler();
this.o = o;
}
private class Handler extends Thread {
public Handler() {
handler = this;
}
@Override
public void run() {
o.takeAction();
}
}
public boolean TestSameObserver(Observer o) {
return o == this.o;
}
public void invoke() {
handler.start();
}
}
class ObservedObject implements Observed {
private Vector<Invoker> observerList = new Vector<Invoker>();
public void addObserver(Observer o) {
observerList.add(new Invoker(o));
}
public void removeObserver(Observer o) {
Iterator<Invoker> it = observerList.iterator();
while (it.hasNext()) {
Invoker i = it.next();
if (i.TestSameObserver(o)) {
observerList.remove(i);
break;
}
}
}
public void update() {
for (Invoker i : observerList) {
i.invoke();
}
}
}
class ObserverA implements Observer {
public void takeAction() {
System.out.println("I am Observer A ,state changed ,so i have to do something");
}
}
class ObserverB implements Observer {
public void takeAction() {
System.out.println("I am Observer B ,i was told to do something");
}
}
class ObserverC implements Observer {
public void takeAction() {
System.out.println("I am Observer C ,I just look ,and do nothing");
}
}
public class Main {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
ObserverA a = new ObserverA();
ObserverB b = new ObserverB();
ObserverC c = new ObserverC();
ObservedObject oo = new ObservedObject();
oo.addObserver(a);
oo.addObserver(b);
oo.addObserver(c);
for (int i = 0; i < 5; ++i) {
oo.addObserver(new Observer() {
public void takeAction() {
System.out.println("我是山寨觀察者"+"，誰敢攔我");
}
});
}
//sometime oo changed ,so it calls update and informs all observer
oo.update();
}
}
觀察者模式的精髓在於註冊壹個觀察者觀測可能隨時變化的對象，對象變化時就會自動通知觀察者，
這樣在被觀測對象影響範圍廣，可能引起多個類的行為改變時很好用，因為無需修改被觀測對象的代碼就可以增加被觀測對象影響的類，這樣的設計模式使得代碼易於管理和維護，並且減少了出錯幾率
至於異步機制實際是個噱頭，可以有觀測對象來實現異步，也可以有觀察者自身實現，這個程序實際是觀測對象實現了異步機制，方法是在觀察者類外包裝了壹層invoker類