设计模式之观察者模式

Subject.java

public interface Subject {

    public void registerObserver(Observer o);

    public void removeObserver(Observer o);

    public void notifyObservers();

}

Observer.java

public interface Observer {

    public void update(float temp, float humidity, float pressure);

}

DisplayElement.java

public interface DisplayElement {

    public void display();

}

WeatherStation.java

public class WeatherStation {

    public static void main(String[] args) {
        WeatherData weatherData = new WeatherData();
        CurrentConditionDisplay currentDisplay = new CurrentConditionDisplay(
                weatherData);
        weatherData.setMeasurements(80, 65, 30.4f);
        weatherData.setMeasurements(82, 70, 29.2f);
        weatherData.setMeasurements(78, 90, 29.2f);
    }
}

WeatherData.java

import java.util.ArrayList;

public class WeatherData implements Subject {

    private ArrayList observers;
    private float temperature;
    private float humidity;
    private float pressure;

    public WeatherData() {
        observers = new ArrayList<>();
    }

    @Override
    public void registerObserver(Observer o) {
        observers.add(o);
    }

    @Override
    public void removeObserver(Observer o) {
        int i = observers.indexOf(o);
        if (i >= 0) {
            observers.remove(i);
        }
    }

    @Override
    public void notifyObservers() {
        for (int i = 0; i < observers.size(); i++) {
            Observer observer = (Observer) observers.get(i);
            observer.update(temperature, humidity, pressure);
        }
    }

    public void measurementsChanged(){
        notifyObservers();
    }

    public void setMeasurements(float temperature, float humidity, float pressure){
        this.temperature = temperature;
        this.humidity = humidity;
        this.pressure = pressure;
        measurementsChanged();
    }   
}

CurrentConditionDisplay.java

public class CurrentConditionDisplay implements Observer, DisplayElement {

    private float temperature;
    private float humidity;
    private Subject weatherData;

    public CurrentConditionDisplay(Subject weatherData) {
        this.weatherData = weatherData;
        weatherData.registerObserver(this);
    }

    @Override
    public void display() {
        System.out.println("Current Conditions:" + temperature
                + "F degrees and " + humidity + "% humidity");
    }

    @Override
    public void update(float temperature, float humidity, float pressure) {
        this.temperature = temperature;
        this.humidity = humidity;
        display();
    }
}