观察者模式又叫做发布-订阅模式：定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象。这个主题对象在状态发生变化时，会通知所有观察者对象，使它们能够自动更新自己。
观察者模式所做的工作其实就是在解除耦合，让耦合的双方都依赖于抽象，而不是依赖于具体，从而使得各自的变化都不会影响另一边的变化。
代码如下：
package xiao;
import java.util.ArrayList;
import
java.util.List;
interface Subject{
void
Attach(Observer observer);
void Detach(Observer
observer);
void Notify();
String
getSubjectState();
void setSubjectState(String
subjectState);
}
abstract class Observer{
protected String name;
protected Secretary
sub;
public abstract void update();
}
class
Secretary implements Subject{
private List<Observer>
observers = new ArrayList<Observer>();
private
String subjectState;
public void Attach(Observer
observer){
observers.add(observer);
}
public void Detach(Observer observer){
observers.remove(observer);
}
public void Notify(){
for(Observer o:observers){
o.update();
}
}
public String
getSubjectState() {
return
subjectState;
}
@Override
public void setSubjectState(String
subjectState) {
this.subjectState =
subjectState;
}
}
class StockObserver extends Observer
{
public StockObserver(String name,Secretary sub){
this.name = name;
this.sub = sub;
}
public void
update(){
System.out.println(sub.getSubjectState()+this.name+"关闭股票，继续工作");
}
}
class NBAObserver extends Observer
{
public NBAObserver(String name,Secretary sub){
this.name = name;
this.sub = sub;
}
public void
update(){
System.out.println(sub.getSubjectState()+this.name+"关闭NBA，继续工作");
}
}
public class abc {
public static void
main(String[] args) {
Secretary
tongzizhe = new Secretary();
StockObserver tongshi1 = new StockObserver("mike",
tongzizhe);
NBAObserver tongshi2 = new
NBAObserver("dave", tongzizhe);
tongzizhe.Attach(tongshi2);
tongzizhe.Attach(tongshi1);
tongzizhe.setSubjectState("boss is coming ");
tongzizhe.Notify();
}
}
Chapter 14 观察者模式,布布扣,bubuko.com
原文：http://www.cnblogs.com/tuifeideyouran/p/3742742.html