先举列子,对Observable有点感觉....
观察者为羊,被观察者为狼 模仿的场景为狼叫羊跑
代码如下:
1.被观察者类
package test.pattern.observer;
import java.util.Observable;
public class Wolf extends Observable{
private String name;
Wolf(String name) {
this.name = name;
}
public void cry(String state){
System.out.println(this.getName()+ " crying ");
this.setChanged();
this.notifyObservers(state);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
2.观察者类
package test.pattern.observer;
import java.util.Observable;
import java.util.Observer;
public class Sheep implements Observer {
private String state = "eating";
private String name;
public Sheep(String name){
this.name = name;
}
public void update(Observable o, Object arg) {
// TODO Auto-generated method stub
Wolf wolf = (Wolf)o;
System.out.println(wolf.getName()+" crying and "+arg+" "+this.getName()+" running.....");
setState("running");
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
3.测试
package test.pattern.observer;
public class TestObserver {
public static void main(String[] args) {
Wolf wolf = new Wolf("wolf1");
Sheep sheep1 = new Sheep("sheep1");
Sheep sheep2 = new Sheep("sheep2");
Sheep sheep3 = new Sheep("sheep3");
//注册观察者,sheep1,sheep2加入,sheep3未加入
wolf.addObserver(sheep1);
wolf.addObserver(sheep2);
String wolfStat = "hungry";
//wolf begin cry
wolf.cry(wolfStat);
}
}
4.结果:
wolf1 crying
wolf1 crying and hungry sheep2 running.....
wolf1 crying and hungry sheep1 running.....
------------------------------*****************-------------------------------
下面,再具体分析观察者模式每一块功能
------------------------------*****************-------------------------------
在Java中通过Observable类和Observer接口实现了观察者模式。Observer对象是观察者,Observable对象是被观察者。
1. 实现观察者模式
实现观察者模式非常简单,
[1]创建被观察者类,它继承自java.util.Observable类;
[2]创建观察者类,它实现java.util.Observer接口;
[3]对于被观察者类,
添加它的观察者:
void addObserver(Observer o)
addObserver()方法把观察者对象添加到观察者对象列表中。
当被观察事件发生时,执行:
setChanged();
notifyObservers();
setChange()方法用来设置一个内部标志位注明数据发生了变化;notifyObservers()方法会去调用观察者对象列表中
所有的Observer的update()方法,通知它们数据发生了变化。
只有在setChange()被调用后,notifyObservers()才会去调用update()。
[4]对于观察者类,实现Observer接口的唯一方法update
void update(Observable o, Object arg)
形参Object arg,对应一个由notifyObservers(Object arg);传递来的参数,
当执行的是notifyObservers();时,arg为null。
2.实例一
NumObserable是一个被观察者,当它的成员变量data的数值发生变化时,会通知所有的观察者。
NumObserable.java
package com.zj.observer;
import java.util.Observable;
public class NumObservable extends Observable {
private int data = 0;
public int getData() {
return data;
}
public void setData(int i) {
data = i;
setChanged();
notifyObservers();
}
}
NumObserver是观察者。当它的被观察者(NumObserable)执行了notifyObservers()后,它会执行uodate()方法。
NumObserver.java
package com.zj.observer;
import java.util.Observable;
import java.util.Observer;
public class NumObserver implements Observer{
public void update(Observable o, Object arg) {
NumObservable myObserable=(NumObservable) o;
System.out.println("Data has changed to " +myObserable.getData());
}
}
测试类SingleTest,在这里将观察者加入到被观察者的观察列表中。
SingleTest.java
package com.zj.observer;
public class SingleTest {
public static void main(String[] args) {
NumObservable number = new NumObservable();
number.addObserver(new NumObserver());
number.setData(1);
number.setData(2);
number.setData(3);
}
}
结果:
Data has changed to 1
Data has changed to 2
Data has changed to 3
3.实例二
这个实例中,还是对data进行观察,拥有两个观察者,分别观察奇数和偶数的变化,
通过notifyObservers(arg)中的参数arg来识别通知信息。
被观察者NumsObservable.java
package com.zj.observers;
import java.util.Observable;
public class NumsObservable extends Observable {
public final static Integer ODD = 1;
public final static Integer EVEN = 2;
private int data = 0;
public int getData() {
return data;
}
public void setData(int i) {
data = i;
Integer flag = EVEN;
if ((data & 0x0001) == 1)
flag = ODD;
setChanged();
notifyObservers(flag);
}
}
奇数观察者OddObserver.java
package com.zj.observers;
import java.util.Observable;
import java.util.Observer;
public class OddObserver implements Observer {
public void update(Observable o, Object arg) {
if (arg == NumsObservable.ODD) {
NumsObservable myObserable = (NumsObservable) o;
System.out.println("OddObserver:Data has changed to " + myObserable.getData());
}
}
}
偶数观察者EvenObserver.java
package com.zj.observers;
import java.util.Observable;
import java.util.Observer;
public class EvenObserver implements Observer {
public void update(Observable o, Object arg) {
if (arg == NumsObservable.EVEN) {
NumsObservable myObserable = (NumsObservable) o;
System.out.println("EvenObserver:Data has changed to " + myObserable.getData());
}
}
}
测试类MultiTest.java
package com.zj.observers;
public class MultiTest {
public static void main(String[] args) {
NumsObservable number = new NumsObservable();
number.addObserver(new OddObserver());
number.addObserver(new EvenObserver());
number.setData(1);
number.setData(2);
number.setData(3);
}
}
结果:
OddObserver:Data has changed to 1
EvenObserver:Data has changed to 2
OddObserver:Data has changed to 3
------------------------------------*********************----------------------------
转载:http://blog.youkuaiyun.com/dada360778512/article/details/6977758