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Commit cb40f1c

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joningiworkjoningiwork
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Added example of generic observer
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+125Lines changed: 125 additions & 0 deletions

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‎observer/src/main/java/com/iluwatar/App.java‎

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package com.iluwatar;
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import com.iluwatar.generic.GHobbits;
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import com.iluwatar.generic.GOrcs;
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import com.iluwatar.generic.GWeather;
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/**
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*
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* Observer pattern defines one-to-many relationship between objects. The target
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weather.timePasses();
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weather.timePasses();
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// Generic observer inspired by Java Generics and Collection by Naftalin & Wadler
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GWeather gWeather = new GWeather();
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gWeather.addObserver(new GHobbits());
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gWeather.addObserver(new GOrcs());
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gWeather.timePasses();
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gWeather.timePasses();
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gWeather.timePasses();
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gWeather.timePasses();
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}
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}
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‎observer/src/main/java/com/iluwatar/generic/GHobbits.java‎

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package com.iluwatar.generic;
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import com.iluwatar.WeatherType;
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public class GHobbits implements Race {
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@Override
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public void update(GWeather o, WeatherType weatherType) {
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switch (weatherType) {
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case COLD:
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System.out.println("The hobbits are shivering in the cold weather.");
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break;
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case RAINY:
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System.out.println("The hobbits look for cover from the rain.");
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break;
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case SUNNY:
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System.out.println("The happy hobbits bade in the warm sun.");
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break;
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case WINDY:
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System.out.println("The hobbits hold their hats tightly in the windy weather.");
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break;
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default:
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break;
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}
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}
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}
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‎observer/src/main/java/com/iluwatar/generic/GOrcs.java‎

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package com.iluwatar.generic;
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import com.iluwatar.WeatherType;
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public class GOrcs implements Race {
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@Override
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public void update(GWeather weather, WeatherType weatherType) {
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switch (weatherType) {
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case COLD:
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System.out.println("The orcs are freezing cold.");
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break;
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case RAINY:
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System.out.println("The orcs are dripping wet.");
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break;
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case SUNNY:
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System.out.println("The sun hurts the orcs' eyes.");
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break;
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case WINDY:
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System.out.println("The orc smell almost vanishes in the wind.");
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break;
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default:
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break;
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}
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}
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}
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‎observer/src/main/java/com/iluwatar/generic/GWeather.java‎

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package com.iluwatar.generic;
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import com.iluwatar.WeatherType;
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public class GWeather extends Observable<GWeather, Race, WeatherType> {
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private WeatherType currentWeather;
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public GWeather() {
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currentWeather = WeatherType.SUNNY;
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}
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public void timePasses() {
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WeatherType[] enumValues = WeatherType.values();
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currentWeather = enumValues[(currentWeather.ordinal() + 1) % enumValues.length];
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System.out.println("The weather changed to " + currentWeather + ".");
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notifyObservers(currentWeather);
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}
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}
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‎observer/src/main/java/com/iluwatar/generic/Observable.java‎

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package com.iluwatar.generic;
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import java.util.List;
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import java.util.concurrent.CopyOnWriteArrayList;
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/**
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* Generic observer inspired by Java Generics and Collection by Naftalin & Wadler
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*
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* @param <S> Subject
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* @param <O> Observer
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* @param <A> Argument type
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*/
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public abstract class Observable<S extends Observable<S, O, A>, O extends Observer<S, O, A>, A> {
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protected List<O> observers;
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public Observable() {
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this.observers = new CopyOnWriteArrayList<>();
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}
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public void addObserver(O observer) {
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this.observers.add(observer);
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}
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@SuppressWarnings("unchecked")
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public void notifyObservers(A argument) {
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for (O observer : observers) {
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observer.update((S) this, argument);
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}
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}
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}
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‎observer/src/main/java/com/iluwatar/generic/Observer.java‎

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package com.iluwatar.generic;
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public interface Observer<S extends Observable<S, O, A>, O extends Observer<S, O, A>, A> {
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public void update(S subject, A argument);
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}
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‎observer/src/main/java/com/iluwatar/generic/Race.java‎

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package com.iluwatar.generic;
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import com.iluwatar.WeatherType;
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public interface Race extends Observer<GWeather, Race, WeatherType> {
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}

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