设计模式--观察者模式

public interface Subject {
  public void registerObesrver(Observer observer);

  public void removeObeserver(Observer observer);

  public void notifyObeservers();
}

public class WeatherData implements Subject {
  private Double temperate = null;

  // ArrayList默认容量为10，当大量添加observers，可能存在性能问题
  private List<Observer> observers = new ArrayList<>();

  public Double getTemperate() {
    return temperate;
  }

  public void setTemperate(Double temperate) {
    this.temperate = temperate;
    notifyObeservers();
  }

  @Override
  public void registerObesrver(Observer observer) {
    observers.add(observer);
  }

  @Override
  public void removeObeserver(Observer observer) {
    observers.remove(observer);
  }

  @Override
  public void notifyObeservers() {
    for (Observer observer : observers) {
      observer.update();
    }
  }


}

public interface Observer {
  public void update();
}

public class TvOberser implements Observer {

  private WeatherData weatherData;

  public TvOberser(WeatherData weatherData) {
    this.weatherData = weatherData;
    weatherData.registerObesrver(this);
  }

  @Override
  public void update() {
    System.out.println("**************************");
    System.out.println("*********  TV  ***********");
    System.out.println("temperate:" + weatherData.getTemperate());
    System.out.println("**************************");

  }
}

public class RadioObserver implements Observer {

  public WeatherData weatherData;

  public RadioObserver(WeatherData weatherData) {
    this.weatherData = weatherData;
    weatherData.registerObesrver(this);
  }

  @Override
  public void update() {
    System.out.println("-----------------------------");
    System.out.println("---------  Radio  -----------");
    System.out.println("temperate:" + weatherData.getTemperate());
    System.out.println("-----------------------------");
  }
}

public class Main {
  public static void main(String args[]) {
    WeatherData weatherData = new WeatherData();
    TvOberser tvOberser = new TvOberser(weatherData);
    RadioObserver radioObserver = new RadioObserver(weatherData);
    weatherData.setTemperate(100.0);
    weatherData.setTemperate(99.0);
    weatherData.setTemperate(98.0);
    weatherData.setTemperate(96.0);
  }
}