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| | {{NAVPO}} | | {{NAVPO}} |
| − | <!--{{TOCright}}-->
| + | {{TOCright}} |
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| | O padrão ''observer'' permite observar o estado de um objecto. Os observadores registam o seu interesse no estado junto do objecto; quando o estado do objecto muda, os observadores são notificados. | | O padrão ''observer'' permite observar o estado de um objecto. Os observadores registam o seu interesse no estado junto do objecto; quando o estado do objecto muda, os observadores são notificados. |
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| | ==Exemplo== | | ==Exemplo== |
| | | | |
| − | ===Observadores e Observados===
| + | * [[Observer (padrão de desenho)/Exemplo 01: Estação Meteorológica|Exemplo 01: Estação Meteorológica]] |
| | | | |
| − | <java5>
| + | [[category:Ensino]] |
| − | public interface Subject {
| + | [[category:PO]] |
| − | public void registerObserver(Observer o);
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| − | public void removeObserver(Observer o);
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| − | public void notifyObservers();
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| − | }
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| − | </java5>
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| − | | |
| − | <java5>
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| − | public interface Observer {
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| − | public void update(float temp, float humidity, float pressure);
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| − | }
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| − | </java5>
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| − | | |
| − | ===Apresentação===
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| − | | |
| − | Esta interface define o método básico para apresentação de dados.
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| − | | |
| − | <java5>
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| − | public interface DisplayElement {
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| − | public void display();
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| − | }
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| − | </java5>
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| − | | |
| − | As implementações da interface de apresentação, que implementam também a de observação, definem várias formas de exibição de dados.
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| − | | |
| − | <java5>
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| − | public class CurrentConditionsDisplay implements Observer, DisplayElement {
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| − | private float _temperature;
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| − | private float _humidity;
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| − | private Subject _weatherData;
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| − |
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| − | public CurrentConditionsDisplay(Subject weatherData) {
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| − | _weatherData = weatherData;
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| − | _weatherData.registerObserver(this);
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| − | }
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| − | | |
| − | public void update(float temperature, float humidity, float pressure) {
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| − | _temperature = temperature;
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| − | _humidity = humidity;
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| − | display();
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| − | }
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| − | | |
| − | public void display() {
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| − | System.out.println("Current conditions: " + _temperature + "F degrees and " + _humidity + "% humidity");
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| − | }
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| − | }
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| − | </java5>
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| − | | |
| − | <java5>
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| − | public class ForecastDisplay implements Observer, DisplayElement {
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| − |
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| − | private float _currentPressure = 29.92f;
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| − | private float _lastPressure;
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| − | private WeatherData _weatherData;
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| − |
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| − | public ForecastDisplay(WeatherData weatherData) {
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| − | _weatherData = weatherData;
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| − | _weatherData.registerObserver(this);
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| − | }
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| − | | |
| − | public void update(float temp, float humidity, float pressure) {
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| − | _lastPressure = currentPressure;
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| − | _currentPressure = pressure;
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| − | display();
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| − | }
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| − | | |
| − | public void display() {
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| − | System.out.print("Forecast: ");
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| − | if (_currentPressure > _lastPressure) {
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| − | System.out.println("Improving weather on the way!");
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| − | } else if (_currentPressure == _lastPressure) {
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| − | System.out.println("More of the same");
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| − | } else if (_currentPressure < _lastPressure) {
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| − | System.out.println("Watch out for cooler, rainy weather");
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| − | }
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| − | }
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| − | }
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| − | </java5>
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| − | | |
| − | ===Representação de dados===
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| − | | |
| − | Os dados de meteorologia correspondem ao objecto observado.
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| − | | |
| − | <java5>
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| − | public class WeatherData implements Subject {
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| − | private ArrayList<Observer> _observers = new ArrayList<Observer>();
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| − | private float _temperature;
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| − | private float _humidity;
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| − | private float _pressure;
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| − |
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| − | public WeatherData() { }
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| − |
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| − | public void registerObserver(Observer o) { _observers.add(o); }
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| − |
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| − | public void removeObserver(Observer o) {
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| − | int i = _observers.indexOf(o);
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| − | if (i >= 0) { _observers.remove(i); }
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| − | }
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| − |
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| − | public void notifyObservers() {
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| − | for (int i = 0; i < _observers.size(); i++) {
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| − | Observer observer = _observers.get(i);
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| − | observer.update(temperature, humidity, pressure);
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| − | }
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| − | }
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| − |
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| − | public void measurementsChanged() { notifyObservers(); }
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| − |
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| − | public void setMeasurements(float temperature, float humidity, float pressure) {
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| − | _temperature = temperature;
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| − | _humidity = humidity;
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| − | _pressure = pressure;
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| − | measurementsChanged();
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| − | }
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| − | | |
| − | }
| |
| − | </java5>
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| − | | |
| − | ===Dois contextos===
| |
| − | | |
| − | Os dois contextos de utilização correspondem a duas estações meteorológicas: em cada uma são utilizados observadores diferentes sobre os mesmos dados.
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| − | | |
| − | <B>public</B> <B>class</B> WeatherStation {
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| − | <B>public</B> <FONT COLOR="#800000">static</FONT> <FONT COLOR="#800000">void</FONT> <FONT COLOR="#000080">main</FONT>(<B><FONT COLOR="#0095ff">String</FONT></B>[] args) {
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| − | WeatherData weatherData = <B>new</B> <FONT COLOR="#000080">WeatherData</FONT>();
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| − |
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| − | CurrentConditionsDisplay currentDisplay = <B>new</B> <FONT COLOR="#000080">CurrentConditionsDisplay</FONT>(weatherData);
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| − | StatisticsDisplay statisticsDisplay = <B>new</B> <FONT COLOR="#000080">StatisticsDisplay</FONT>(weatherData);
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| − | ForecastDisplay forecastDisplay = <B>new</B> <FONT COLOR="#000080">ForecastDisplay</FONT>(weatherData);
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| − |
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| − | weatherData.<FONT COLOR="#000080">setMeasurements</FONT>(<FONT COLOR="#0000ff">80</FONT>, <FONT COLOR="#0000ff">65</FONT>, <FONT COLOR="#800080">30.4f</FONT>);
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| − | weatherData.<FONT COLOR="#000080">setMeasurements</FONT>(<FONT COLOR="#0000ff">82</FONT>, <FONT COLOR="#0000ff">70</FONT>, <FONT COLOR="#800080">29.2f</FONT>);
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| − | weatherData.<FONT COLOR="#000080">setMeasurements</FONT>(<FONT COLOR="#0000ff">78</FONT>, <FONT COLOR="#0000ff">90</FONT>, <FONT COLOR="#800080">29.2f</FONT>);
| |
| − | }
| |
| − | }
| |
| − | | |
| − | <B>public</B> <B>class</B> WeatherStationHeatIndex {
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| − | <B>public</B> <FONT COLOR="#800000">static</FONT> <FONT COLOR="#800000">void</FONT> <FONT COLOR="#000080">main</FONT>(<B><FONT COLOR="#0095ff">String</FONT></B>[] args) {
| |
| − | WeatherData weatherData = <B>new</B> <FONT COLOR="#000080">WeatherData</FONT>();
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| − |
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| − | CurrentConditionsDisplay currentDisplay = <B>new</B> <FONT COLOR="#000080">CurrentConditionsDisplay</FONT>(weatherData);
| |
| − | StatisticsDisplay statisticsDisplay = <B>new</B> <FONT COLOR="#000080">StatisticsDisplay</FONT>(weatherData);
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| − | ForecastDisplay forecastDisplay = <B>new</B> <FONT COLOR="#000080">ForecastDisplay</FONT>(weatherData);
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| − | HeatIndexDisplay heatIndexDisplay = <B>new</B> <FONT COLOR="#000080">HeatIndexDisplay</FONT>(weatherData);
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| − |
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| − | weatherData.<FONT COLOR="#000080">setMeasurements</FONT>(<FONT COLOR="#0000ff">80</FONT>, <FONT COLOR="#0000ff">65</FONT>, <FONT COLOR="#800080">30.4f</FONT>);
| |
| − | weatherData.<FONT COLOR="#000080">setMeasurements</FONT>(<FONT COLOR="#0000ff">82</FONT>, <FONT COLOR="#0000ff">70</FONT>, <FONT COLOR="#800080">29.2f</FONT>);
| |
| − | weatherData.<FONT COLOR="#000080">setMeasurements</FONT>(<FONT COLOR="#0000ff">78</FONT>, <FONT COLOR="#0000ff">90</FONT>, <FONT COLOR="#800080">29.2f</FONT>);
| |
| − | }
| |
| − | }
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| − | | |
| − | [[category:OOP]]
| |
| − | [[category:Teaching]] | |
| − | [[category:PO Exemplos]] | |
As colaborações entre os intervenientes são as que figuram no seguinte diagrama de sequência:
