java设计模式：区别对待的观察者模式

观察者模式应用广泛，尤其是在一些网络社交应用的推送功能中的应用更是十分广泛；因为这种模式对于此类应用具有先天优势，它能很方便的进行广播；
使用场景主要有：1.一种对象的操作依赖于另一方面的变化
2.更改一个对象是连带需要更改其一些他对象
一句话来说就是广播模型。
java本身内置了观察者模式的接口（java.util下），但在更为复杂的环境中，我们往往要自定义接口，以满足多样的需求。
同时，一个观察者，有时需要观察多个对象，当然，这个是要根据问题具体情况;
以下的demo是个一个观察者观察两个对象--天气，商品，同时通过标记来区别对待观察者

public interface WeatherSubject
{
public static final int QING = 4;
public static final int YU = 1;
public static final int QING2YU = 2;
public static final int FENG = 3;
public static final int ERROR = 0;

public void attach(WeatherObserver observer);

public void detach(WeatherObserver observer);

public void notifyWeatherObserver();

}

public interface WeatherObserver
{
public void updateWeather(WeatherSubject subject);
public boolean isInWeatherFlags(int f);
}

public interface ShopSubject
{
public static final int ERROR=0;
public static final int FOOD=1;
public static final int TOOL=2;
public static final int BED=3;

public void attach(ShopObserver observer);

public void detach(ShopObserver observer);

public void notifyShopObserver();

}

public interface ShopObserver
{
public void updateShop(ShopSubject subject);
public boolean isInShopFlags(int f);
}

public class ChinaWeatherSubject implements WeatherSubject
{

List<WeatherObserver> observers = new ArrayList<WeatherObserver>();
String weatherContent;
int flag = ERROR;

private String calculateWeather()
{
    Random random = new Random();
    switch(random.nextInt(5))
    {
    case 1:
        flag = QING;
        return "今天，天气晴好";
    case 2:
        flag = YU;
        return "今天，狂风暴雨";
    case 3:
        flag = QING2YU;
        return "雨夹雪转晴";
    case 4:
        flag = FENG;
        return "今天下午，6级大风";
    }
    flag = ERROR;
    return "获取天气失败";
}

public String getWeatherContent() {
    return weatherContent;
}

public void setWeatherContent() {
    this.weatherContent = calculateWeather();
    notifyWeatherObserver();
}

public void attach(WeatherObserver observer) {
    observers.add(observer);
}

public void detach(WeatherObserver observer) {
    observers.remove(observer);
}

public void notifyWeatherObserver() {
    for(WeatherObserver o : observers)
    {
        if(o.isInWeatherFlags(flag)) o.updateWeather(this);
    }
}

}

public class TianMaoShopSubject implements ShopSubject
{
List<ShopObserver> observers = new ArrayList<ShopObserver>();
String shopContent;
int flag = ERROR;

private String calculateShop()
{
    Random random = new Random();
    switch(random.nextInt(4))
    {
    case 1:
        flag = BED;
        return "床上用品";
    case 2:
        flag = FOOD;
        return "食物";
    case 3:
        flag = TOOL;
        return "日用工具";
    }
    flag = ERROR;
    return "获取商品失败";
}

public void attach(ShopObserver observer) {
    observers.add(observer);
}

public void detach(ShopObserver observer) {
    observers.remove(observer);
}

public void notifyShopObserver() {
    for(ShopObserver o : observers)
    {
        if(o.isInShopFlags(flag)) o.updateShop(this);
    }
}

public String getShopContent() {
    return shopContent;
}

public void setShopContent() {
    this.shopContent = calculateShop();
    notifyShopObserver();
}

}

public class AppObserver implements WeatherObserver,ShopObserver
{
String username;
List<Integer> weatherFlags = new ArrayList<Integer>();
List<Integer> shopFlags = new ArrayList<Integer>();

public AppObserver(String uname,int[] wFlag,int[] sFlag) {
    username = uname;
    setWeatherFlags(wFlag);
    setShopFlags(sFlag);
}

public void setWeatherFlags(int[] wFlag)
{
    for(int i=0;i<wFlag.length;i++)
    {
        weatherFlags.add(wFlag[i]);
    }
}

public void setShopFlags(int[] sFlag)
{
    for(int i=0;i<sFlag.length;i++)
    {
        shopFlags.add(sFlag[i]);
    }
}

public boolean isInWeatherFlags(int f) {
    return weatherFlags.contains(f);
}

public boolean isInShopFlags(int f) {
    return shopFlags.contains(f);
}

public void updateWeather(WeatherSubject subject) {
    System.out.println(username+"收到天气消息 ; 天气情况是:"+((ChinaWeatherSubject)subject).getWeatherContent());
}

public void updateShop(ShopSubject subject) {
    System.out.println(username+"收到商店消息 ; 货物情况是:"+((TianMaoShopSubject)subject).getShopContent());
}

}

public class ObserverTest {

public static void main(String[] args) {
    ChinaWeatherSubject subject = new ChinaWeatherSubject();
    TianMaoShopSubject subject0 = new TianMaoShopSubject();
    AppObserver o1 = new AppObserver("凌风",new int[]{
        WeatherSubject.FENG,    
    },new int[]{
        ShopSubject.BED,    
    });
    AppObserver o2 = new AppObserver("雪情",new int[]{
        WeatherSubject.QING2YU,
    },new int[]{
        ShopSubject.FOOD,   
    });
    AppObserver o3 = new AppObserver("莎莎",new int[]{
        WeatherSubject.YU,  
        WeatherSubject.QING2YU,
        WeatherSubject.QING,
        WeatherSubject.FENG,
    },new int[]{
        ShopSubject.BED,
        ShopSubject.FOOD,
        ShopSubject.TOOL,
    });

    subject.attach(o1);
    subject.attach(o2);
    subject.attach(o3);
    subject0.attach(o1);
    subject0.attach(o2);
    subject0.attach(o3);

    subject.setWeatherContent();
    subject0.setShopContent();
}

}
运行效果：