给某个对象一个设置一个观察者，以便能敏感捕捉到对象的变化
package observer;

import java.util.*;


public class Product extends Observable {
private String name;
private float price;
public String getName() {
return name;
}

public float getPrice() {
return price;
}

private int id;

public Product(int id, String name, float price) {
this.id = id;
this.name = name;
this.price = price;
}
public int getId() {
return id;
}
public void setName(String name) {
this.name = name;
setChanged();
notifyObservers("name");
}
public void setPrice(float price) {
this.price = price;
setChanged();
notifyObservers("price");
//notifyObservers();
}
}
****************************************************************
package observer;

import java.util.*;

public class PriceObserver implements Observer {
private float price = 0;
public void update(Observable obj, Object arg) {

try{
if (arg instanceof String) {
String argName = (String)arg;
if(argName.trim().equalsIgnoreCase("price")){
int id = 0;
float price = 0;
String test = "";
if(obj instanceof Product){
Product pro = (Product)obj;
price = pro.getPrice();
id = pro.getId();
}

System.out.println("PriceObserver : Product "+id+" \'s pirce has changed to " + price);
}
}

}catch(Exception ex){
ex.printStackTrace();
}

}
}
*********************************************************************
package observer;

import java.util.*;
public class NameObserver implements Observer {
private String name = null;
public void update(Observable obj, Object arg) {
try{

if (arg instanceof String) {
String argName = (String)arg;
if(argName.trim().equalsIgnoreCase("name")){
int id = 0;
String name = "";
if(obj instanceof Product){
Product pro = (Product)obj;
name = pro.getName();
id = pro.getId();
}
System.out.println("NameObserver : Product "+id+" \'s name has changed to " + name);
}
}


}catch(Exception ex){
ex.printStackTrace();
}
}
}
*********************************************************************
package observer;

public class Main {
public static void main(String args[]) {
Product product = new Product(1,"桔子",(float)9.20);
//Product product = new Product();
NameObserver nameobs = new NameObserver();
PriceObserver priceobs = new PriceObserver();
product.addObserver(nameobs);
product.addObserver(priceobs);
product.setName("苹果");
product.setPrice(12.80f);
product.setName("香蕉");
product.setPrice(6.00f);
}
}