public interface Subject {public void registerObserver(Observer o);public void removeObserver(Observer o);public void notifyObservers();}public interface Observer {public void update(float temp, float humidity, float pressure);}public interface DisplayElement {public void display();}

public class CurrentConditionsDisplay implements Observer, DisplayElement {  private float temperature;  private float humidity;  private Subject weatherData;  public CurrentConditionsDisplay(Subject weatherData) {  this.weatherData =http://www.mamicode.com/ weatherData;  weatherData.registerObserver(this);  }  public void update(float temperature, float humidity, float pressure) {  this.temperature = temperature;  this.humidity = humidity;  display();  }  public void display() {  System.out.println(“Current conditions: “ + temperature  + “F degrees and “ + humidity + “% humidity”);  }
}

public class WeatherData implements Subject {  private ArrayList observers;  private float temperature;  private float humidity;  private float pressure;  public WeatherData() {  observers = new ArrayList();}  public void registerObserver(Observer o) {  observers.add(o);}  public void removeObserver(Observer o) {  int i = observers.indexOf(o);  if (i >= 0) {  observers.remove(i);}}  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();}// other WeatherData methods here}