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| ==Exemplo== | | ==Exemplo== |
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| ===Observadores e Observados===
| | * [[Observer (padrão de desenho)/Exemplo 01: Estação Meteorológica|Exemplo 01: Estação Meteorológica]] |
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| <java5>
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| public interface Subject {
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| 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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| }
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| </java5>
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| ===Dois contextos===
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| 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>);
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| }
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| }
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| <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) {
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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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| 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>);
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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>);
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| }
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| }
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|
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| [[category:Ensino]] | | [[category:Ensino]] |
| [[category:PO]] | | [[category:PO]] |
| [[category:PO Exemplos]]
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| [[category:Java]]
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