weather station observer

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 = 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
}