(→Apresentação) |
(→Observadores e Observados) |
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==Observadores e Observados== | ==Observadores e Observados== | ||
− | < | + | <source lang="java"> |
public interface Subject { | public interface Subject { | ||
public void registerObserver(Observer o); | public void registerObserver(Observer o); | ||
Line 7: | Line 7: | ||
public void notifyObservers(); | public void notifyObservers(); | ||
} | } | ||
− | </ | + | </java> |
− | < | + | <source lang="java"> |
public interface Observer { | public interface Observer { | ||
public void update(float temp, float humidity, float pressure); | public void update(float temp, float humidity, float pressure); | ||
} | } | ||
− | </ | + | </source> |
==Apresentação== | ==Apresentação== |
public interface Subject {
public void registerObserver(Observer o);
public void removeObserver(Observer o);
public void notifyObservers();
}
</java>
<source lang="java">
public interface Observer {
public void update(float temp, float humidity, float pressure);
}
Esta interface define o método básico para apresentação de dados.
public interface DisplayElement {
public void display();
}
As implementações da interface de apresentação, que implementam também a de observação, definem várias formas de exibição de dados.
public class CurrentConditionsDisplay implements Observer, DisplayElement {
private float _temperature;
private float _humidity;
private WeatherData _weatherData;
public CurrentConditionsDisplay(WeatherData weatherData) {
_weatherData = weatherData;
_weatherData.registerObserver(this);
}
public void update(float temperature, float humidity, float pressure) {
_temperature = temperature;
_humidity = humidity;
display();
}
public void display() {
System.out.println("Current conditions: " + _temperature + "F degrees and " + _humidity + "% humidity");
}
}
public class ForecastDisplay implements Observer, DisplayElement {
private float _currentPressure = 29.92f;
private float _lastPressure;
private WeatherData _weatherData;
public ForecastDisplay(WeatherData weatherData) {
_weatherData = weatherData;
_weatherData.registerObserver(this);
}
public void update(float temp, float humidity, float pressure) {
_lastPressure = _currentPressure;
_currentPressure = pressure;
display();
}
public void display() {
System.out.print("Forecast: ");
if (_currentPressure > _lastPressure) {
System.out.println("Improving weather on the way!");
} else if (_currentPressure == _lastPressure) {
System.out.println("More of the same");
} else if (_currentPressure < _lastPressure) {
System.out.println("Watch out for cooler, rainy weather");
}
}
}
Os dados de meteorologia correspondem ao objecto observado.
<text>
public class WeatherData implements Subject { private ArrayList<Observer> _observers = new ArrayList<Observer>(); private float _temperature; private float _humidity; private float _pressure; public WeatherData() { } 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 (Observer observer: _observers) { observer.update(_temperature, _humidity, _pressure); } } public void measurementsChanged() { notifyObservers(); } public void setMeasurements(float temperature, float humidity, float pressure) { _temperature = temperature; _humidity = humidity; _pressure = pressure; measurementsChanged(); }
}
</text>
Os dois contextos de utilização correspondem a duas estações meteorológicas: em cada uma são utilizados observadores diferentes sobre os mesmos dados.
public class WeatherStation { public static void main(String[] args) { WeatherData weatherData = new WeatherData(); CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData); StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData); ForecastDisplay forecastDisplay = new ForecastDisplay(weatherData); weatherData.setMeasurements(80, 65, 30.4f); weatherData.setMeasurements(82, 70, 29.2f); weatherData.setMeasurements(78, 90, 29.2f); } }
public class WeatherStationHeatIndex { public static void main(String[] args) { WeatherData weatherData = new WeatherData(); CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData); StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData); ForecastDisplay forecastDisplay = new ForecastDisplay(weatherData); HeatIndexDisplay heatIndexDisplay = new HeatIndexDisplay(weatherData); weatherData.setMeasurements(80, 65, 30.4f); weatherData.setMeasurements(82, 70, 29.2f); weatherData.setMeasurements(78, 90, 29.2f); } }