观察者模式

• 对象之间==多对一依赖==的一种设计模式,被依赖对象为subject,依赖对象为observer,subject通知observer变化,气象站通知网站数据变化.
• 推送和获取
• 用户向站点注册.站点通知所有用户取,或者站点推送

• 无法在运行时动态添加第三方
• 违反oop原则
• 在weather中,当增加一个第三方时,都需要创建一个对应的第三方公告板对象,并加入到datachange()中去,不利于维护,也不是动态加入

//传统示例

main(){
    new Weather(new CurrentCondition).setdata(11f,12f,13f);
}
public class CurrentCondition {
    //温度,气压,湿度
    private float temperature;
    private float pressure;
    private float humidity;
    //更新天气信息,使用推送模式
    public void update(float temperature,float pressure,float humidity) {
        this.temperature=temperature;
        this.pressure=pressure;
        this.humidity=humidity;
        display();
    }
    public void display() {
        System.out.println(temperature+pressure+humidity);
    }
}

public class Weather {
    float temperature;
    float pressure;
    float humidity;
    CurrentCondition currentCondition;

    public Weather(float temperature, float pressure, float humidity, CurrentCondition currentCondition) {
        this.temperature = temperature;
        this.pressure = pressure;
        this.humidity = humidity;
        this.currentCondition = currentCondition;
    }
    //当有数据更新时,调用
    public void setData(float temperature,float pressure,float humidity) {
        this.temperature = temperature;
        this.pressure = pressure;
        this.humidity = humidity;
        //将最新信息推送出去
        dataChange();
    }

    public void dataChange() {
        currentCondition.update(temperature,pressure,humidity);
    }
    //getterandsetter()

}

使用观察者模式改进

main(){
    new Weather();
    new CurrentCondition();
    weather.registerObserver(currentCondition);
    weather.setdata(11f,12f,13f);
}

public interface subject{
    public void registerObserver(Observer o);
    public void removeObserver(Observer o);
    public void notifyall();
}
public interface Observer{
    public update(float temp,float pressure,float huminity);
}
public class CurrentCondition implements Observer{
    //温度,气压,湿度
    private float temperature;
    private float pressure;
    private float humidity;
    //更新天气信息,使用推送模式
    public void update(float temperature,float pressure,float humidity) {
        this.temperature=temperature;
        this.pressure=pressure;
        this.humidity=humidity;
        display();
    }
    public void display() {
        System.out.println(temperature+pressure+humidity);
    }
}
public class Weather implements Subject{
    float temperature;
    float pressure;
    float humidity;
    ArrayList<Observer> observers;

    public Weather(float temperature, float pressure, float humidity, CurrentCondition currentCondition) {
        this.temperature = temperature;
        this.pressure = pressure;
        this.humidity = humidity;
        this.currentCondition = currentCondition;
    }
    //当有数据更新时,调用
    public void setData(float temperature,float pressure,float humidity) {
        this.temperature = temperature;
        this.pressure = pressure;
        this.humidity = humidity;
        //将最新信息推送出去
        dataChange();
    }

    public void registerObserver(Observer o){
        observers.add(o);
    }
    public void removeObserver(Observer o){
        observers.remove(o);
    }
    public void dataChange(){
        notifyall();
    }
    public void notifyall(){
        observers.for(i){
            observers.get(i).update(this.temp,this.pressure,this.huminity);
        }
    }
    
    //getterandsetter()

}