Merge remote-tracking branch 'upstream/master'

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

@@ -6,45 +6,44 @@ import com.iluwatar.observer.generic.GWeather;
 
 /**
  * 
- * The Observer pattern is a software design pattern in which an object, called 
+ * The Observer pattern is a software design pattern in which an object, called the subject,
- * the subject, maintains a list of its dependents, called observers, and notifies 
+ * maintains a list of its dependents, called observers, and notifies them automatically of any
- * them automatically of any state changes, usually by calling one of their methods. 
+ * state changes, usually by calling one of their methods. It is mainly used to implement
- * It is mainly used to implement distributed event handling systems. The Observer 
+ * distributed event handling systems. The Observer pattern is also a key part in the familiar
- * pattern is also a key part in the familiar model–view–controller (MVC) architectural 
+ * model–view–controller (MVC) architectural pattern. The Observer pattern is implemented in
- * pattern. The Observer pattern is implemented in numerous programming libraries and 
+ * numerous programming libraries and systems, including almost all GUI toolkits.
- * systems, including almost all GUI toolkits.
  * <p>
- * In this example {@link Weather} has a state that can be observed. The {@link Orcs}
+ * In this example {@link Weather} has a state that can be observed. The {@link Orcs} and
- * and {@link Hobbits} register as observers and receive notifications when the
+ * {@link Hobbits} register as observers and receive notifications when the {@link Weather} changes.
- * {@link Weather} changes.
  * 
  */
 public class App {
 
-	/**
+  /**
-	 * Program entry point
+   * Program entry point
-	 * @param args command line args
+   * 
-	 */
+   * @param args command line args
-	public static void main(String[] args) {
+   */
+  public static void main(String[] args) {
 
-		Weather weather = new Weather();
+    Weather weather = new Weather();
-		weather.addObserver(new Orcs());
+    weather.addObserver(new Orcs());
-		weather.addObserver(new Hobbits());
+    weather.addObserver(new Hobbits());
 
-		weather.timePasses();
+    weather.timePasses();
-		weather.timePasses();
+    weather.timePasses();
-		weather.timePasses();
+    weather.timePasses();
-		weather.timePasses();
+    weather.timePasses();
 
-		// Generic observer inspired by Java Generics and Collection by Naftalin & Wadler
+    // Generic observer inspired by Java Generics and Collection by Naftalin & Wadler
-		System.out.println("\n--Running generic version--");
+    System.out.println("\n--Running generic version--");
-		GWeather gWeather = new GWeather();
+    GWeather gWeather = new GWeather();
-		gWeather.addObserver(new GOrcs());
+    gWeather.addObserver(new GOrcs());
-		gWeather.addObserver(new GHobbits());
+    gWeather.addObserver(new GHobbits());
 
-		gWeather.timePasses();
+    gWeather.timePasses();
-		gWeather.timePasses();
+    gWeather.timePasses();
-		gWeather.timePasses();
+    gWeather.timePasses();
-		gWeather.timePasses();
+    gWeather.timePasses();
-	}
+  }
 }

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

@@ -7,24 +7,23 @@ package com.iluwatar.observer;
  */
 public class Hobbits implements WeatherObserver {
 
-	@Override
+  @Override
-	public void update(WeatherType currentWeather) {
+  public void update(WeatherType currentWeather) {
-		switch (currentWeather) {
+    switch (currentWeather) {
-		case COLD:
+      case COLD:
-			System.out.println("The hobbits are shivering in the cold weather.");
+        System.out.println("The hobbits are shivering in the cold weather.");
-			break;
+        break;
-		case RAINY:
+      case RAINY:
-			System.out.println("The hobbits look for cover from the rain.");
+        System.out.println("The hobbits look for cover from the rain.");
-			break;
+        break;
-		case SUNNY:
+      case SUNNY:
-			System.out.println("The happy hobbits bade in the warm sun.");
+        System.out.println("The happy hobbits bade in the warm sun.");
-			break;
+        break;
-		case WINDY:
+      case WINDY:
-			System.out.println("The hobbits hold their hats tightly in the windy weather.");
+        System.out.println("The hobbits hold their hats tightly in the windy weather.");
-			break;
+        break;
-		default:
+      default:
-			break;
+        break;
-		}
+    }
-	}
+  }
-
 }

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

@@ -7,24 +7,23 @@ package com.iluwatar.observer;
  */
 public class Orcs implements WeatherObserver {
 
-	@Override
+  @Override
-	public void update(WeatherType currentWeather) {
+  public void update(WeatherType currentWeather) {
-		switch (currentWeather) {
+    switch (currentWeather) {
-		case COLD:
+      case COLD:
-			System.out.println("The orcs are freezing cold.");
+        System.out.println("The orcs are freezing cold.");
-			break;
+        break;
-		case RAINY:
+      case RAINY:
-			System.out.println("The orcs are dripping wet.");
+        System.out.println("The orcs are dripping wet.");
-			break;
+        break;
-		case SUNNY:
+      case SUNNY:
-			System.out.println("The sun hurts the orcs' eyes.");
+        System.out.println("The sun hurts the orcs' eyes.");
-			break;
+        break;
-		case WINDY:
+      case WINDY:
-			System.out.println("The orc smell almost vanishes in the wind.");
+        System.out.println("The orc smell almost vanishes in the wind.");
-			break;
+        break;
-		default:
+      default:
-			break;
+        break;
-		}
+    }
-	}
+  }
-
 }

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

@@ -5,38 +5,38 @@ import java.util.List;
 
 /**
  * 
- * Weather can be observed by implementing {@link WeatherObserver} interface and
+ * Weather can be observed by implementing {@link WeatherObserver} interface and registering as
- * registering as listener.
+ * listener.
  * 
  */
 public class Weather {
 
-	private WeatherType currentWeather;
+  private WeatherType currentWeather;
-	private List<WeatherObserver> observers;
+  private List<WeatherObserver> observers;
 
-	public Weather() {
+  public Weather() {
-		observers = new ArrayList<>();
+    observers = new ArrayList<>();
-		currentWeather = WeatherType.SUNNY;
+    currentWeather = WeatherType.SUNNY;
-	}
+  }
 
-	public void addObserver(WeatherObserver obs) {
+  public void addObserver(WeatherObserver obs) {
-		observers.add(obs);
+    observers.add(obs);
-	}
+  }
 
-	public void removeObserver(WeatherObserver obs) {
+  public void removeObserver(WeatherObserver obs) {
-		observers.remove(obs);
+    observers.remove(obs);
-	}
+  }
 
-	public void timePasses() {
+  public void timePasses() {
-		WeatherType[] enumValues = WeatherType.values();
+    WeatherType[] enumValues = WeatherType.values();
-		currentWeather = enumValues[(currentWeather.ordinal() + 1) % enumValues.length];
+    currentWeather = enumValues[(currentWeather.ordinal() + 1) % enumValues.length];
-		System.out.println("The weather changed to " + currentWeather + ".");
+    System.out.println("The weather changed to " + currentWeather + ".");
-		notifyObservers();
+    notifyObservers();
-	}
+  }
 
-	private void notifyObservers() {
+  private void notifyObservers() {
-		for (WeatherObserver obs : observers) {
+    for (WeatherObserver obs : observers) {
-			obs.update(currentWeather);
+      obs.update(currentWeather);
-		}
+    }
-	}
+  }
 }

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

@@ -7,6 +7,6 @@ package com.iluwatar.observer;
  */
 public interface WeatherObserver {
 
-	void update(WeatherType currentWeather);
+  void update(WeatherType currentWeather);
 
 }

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

@@ -7,11 +7,10 @@ package com.iluwatar.observer;
  */
 public enum WeatherType {
 
-	SUNNY, RAINY, WINDY, COLD;
+  SUNNY, RAINY, WINDY, COLD;
-
-	@Override
-	public String toString() {
-		return this.name().toLowerCase();
-	}
 
+  @Override
+  public String toString() {
+    return this.name().toLowerCase();
+  }
 }

observer/src/main/java/com/iluwatar/observer/generic/GHobbits.java

@@ -8,23 +8,23 @@ import com.iluwatar.observer.WeatherType;
  *
  */
 public class GHobbits implements Race {
-    @Override
+  @Override
-    public void update(GWeather weather, WeatherType weatherType) {
+  public void update(GWeather weather, WeatherType weatherType) {
-        switch (weatherType) {
+    switch (weatherType) {
-            case COLD:
+      case COLD:
-                System.out.println("The hobbits are shivering in the cold weather.");
+        System.out.println("The hobbits are shivering in the cold weather.");
-                break;
+        break;
-            case RAINY:
+      case RAINY:
-                System.out.println("The hobbits look for cover from the rain.");
+        System.out.println("The hobbits look for cover from the rain.");
-                break;
+        break;
-            case SUNNY:
+      case SUNNY:
-                System.out.println("The happy hobbits bade in the warm sun.");
+        System.out.println("The happy hobbits bade in the warm sun.");
-                break;
+        break;
-            case WINDY:
+      case WINDY:
-                System.out.println("The hobbits hold their hats tightly in the windy weather.");
+        System.out.println("The hobbits hold their hats tightly in the windy weather.");
-                break;
+        break;
-            default:
+      default:
-                break;
+        break;
-        }
     }
+  }
 }

observer/src/main/java/com/iluwatar/observer/generic/GOrcs.java

@@ -8,24 +8,24 @@ import com.iluwatar.observer.WeatherType;
  *
  */
 public class GOrcs implements Race {
-	
+
-    @Override
+  @Override
-    public void update(GWeather weather, WeatherType weatherType) {
+  public void update(GWeather weather, WeatherType weatherType) {
-        switch (weatherType) {
+    switch (weatherType) {
-            case COLD:
+      case COLD:
-                System.out.println("The orcs are freezing cold.");
+        System.out.println("The orcs are freezing cold.");
-                break;
+        break;
-            case RAINY:
+      case RAINY:
-                System.out.println("The orcs are dripping wet.");
+        System.out.println("The orcs are dripping wet.");
-                break;
+        break;
-            case SUNNY:
+      case SUNNY:
-                System.out.println("The sun hurts the orcs' eyes.");
+        System.out.println("The sun hurts the orcs' eyes.");
-                break;
+        break;
-            case WINDY:
+      case WINDY:
-                System.out.println("The orc smell almost vanishes in the wind.");
+        System.out.println("The orc smell almost vanishes in the wind.");
-                break;
+        break;
-            default:
+      default:
-                break;
+        break;
-        }
     }
+  }
 }

observer/src/main/java/com/iluwatar/observer/generic/GWeather.java

@@ -9,16 +9,16 @@ import com.iluwatar.observer.WeatherType;
  */
 public class GWeather extends Observable<GWeather, Race, WeatherType> {
 
-    private WeatherType currentWeather;
+  private WeatherType currentWeather;
 
-    public GWeather() {
+  public GWeather() {
-        currentWeather = WeatherType.SUNNY;
+    currentWeather = WeatherType.SUNNY;
-    }
+  }
 
-    public void timePasses() {
+  public void timePasses() {
-        WeatherType[] enumValues = WeatherType.values();
+    WeatherType[] enumValues = WeatherType.values();
-        currentWeather = enumValues[(currentWeather.ordinal() + 1) % enumValues.length];
+    currentWeather = enumValues[(currentWeather.ordinal() + 1) % enumValues.length];
-        System.out.println("The weather changed to " + currentWeather + ".");
+    System.out.println("The weather changed to " + currentWeather + ".");
-        notifyObservers(currentWeather);
+    notifyObservers(currentWeather);
-    }
+  }
 }

observer/src/main/java/com/iluwatar/observer/generic/Observable.java

@@ -12,20 +12,20 @@ import java.util.concurrent.CopyOnWriteArrayList;
  */
 public abstract class Observable<S extends Observable<S, O, A>, O extends Observer<S, O, A>, A> {
 
-    protected List<O> observers;
+  protected List<O> observers;
 
-    public Observable() {
+  public Observable() {
-        this.observers = new CopyOnWriteArrayList<>();
+    this.observers = new CopyOnWriteArrayList<>();
-    }
+  }
 
-    public void addObserver(O observer) {
+  public void addObserver(O observer) {
-        this.observers.add(observer);
+    this.observers.add(observer);
-    }
+  }
 
-    @SuppressWarnings("unchecked")
+  @SuppressWarnings("unchecked")
-    public void notifyObservers(A argument) {
+  public void notifyObservers(A argument) {
-        for (O observer : observers) {
+    for (O observer : observers) {
-            observer.update((S) this, argument);
+      observer.update((S) this, argument);
-        }
     }
+  }
 }

observer/src/main/java/com/iluwatar/observer/generic/Observer.java

@@ -10,5 +10,5 @@ package com.iluwatar.observer.generic;
  */
 public interface Observer<S extends Observable<S, O, A>, O extends Observer<S, O, A>, A> {
 
-    void update(S subject, A argument);
+  void update(S subject, A argument);
 }

observer/src/test/java/com/iluwatar/observer/AppTest.java

@@ -11,9 +11,9 @@ import com.iluwatar.observer.App;
  */
 public class AppTest {
 
-	@Test
+  @Test
-	public void test() {
+  public void test() {
-		String[] args = {};
+    String[] args = {};
-		App.main(args);
+    App.main(args);
-	}
+  }
 }

pom.xml

@@ -56,6 +56,7 @@
 		<module>execute-around</module>
 		<module>property</module>
 		<module>intercepting-filter</module>
+		<module>producer-consumer</module>
 		<module>poison-pill</module>
 		<module>lazy-loading</module>
 		<module>service-layer</module>

producer-consumer/etc/producer-consumer.ucls

@@ -0,0 +1,74 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
+  realizations="true" associations="true" dependencies="false" nesting-relationships="true">  
+  <class id="1" language="java" name="com.iluwatar.producer.consumer.Item" project="producer-consumer" 
+    file="/producer-consumer/src/main/java/com/iluwatar/producer/consumer/Item.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="415" y="378"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="2" language="java" name="com.iluwatar.producer.consumer.Producer" project="producer-consumer" 
+    file="/producer-consumer/src/main/java/com/iluwatar/producer/consumer/Producer.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="150" y="191"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="3" language="java" name="com.iluwatar.producer.consumer.Consumer" project="producer-consumer" 
+    file="/producer-consumer/src/main/java/com/iluwatar/producer/consumer/Consumer.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="675" y="186"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="4" language="java" name="com.iluwatar.producer.consumer.ItemQueue" project="producer-consumer" 
+    file="/producer-consumer/src/main/java/com/iluwatar/producer/consumer/ItemQueue.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="415" y="187"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <association id="5">    
+    <end type="SOURCE" refId="3" navigable="false">      
+      <attribute id="6" name="queue"/>      
+      <multiplicity id="7" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="4" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <association id="8">    
+    <end type="SOURCE" refId="4" navigable="false">      
+      <attribute id="9" name="queue"/>      
+      <multiplicity id="10" minimum="0" maximum="2147483647"/>    
+    </end>    
+    <end type="TARGET" refId="1" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <association id="11">    
+    <end type="SOURCE" refId="2" navigable="false">      
+      <attribute id="12" name="queue"/>      
+      <multiplicity id="13" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="4" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+    sort-features="false" accessors="true" visibility="true">    
+    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
+    <operations public="true" package="true" protected="true" private="true" static="true"/>  
+  </classifier-display>  
+  <association-display labels="true" multiplicity="true"/>
+</class-diagram>

producer-consumer/index.md

@@ -0,0 +1,22 @@
+---
+layout: pattern
+title: Producer Consumer
+folder: producer-consumer
+permalink: /patterns/producer-consumer/
+categories: Other
+tags: Java
+---
+
+**Intent:** Producer Consumer Design pattern is a classic concurrency or threading pattern which reduces
+ coupling between Producer and Consumer by separating Identification of work with Execution of
+ Work..
+
+
+
+![alt text](./etc/producer-consumer.png "Producer Consumer")
+
+**Applicability:** Use the Producer Consumer idiom when
+
+* decouple system by separate work in two process produce and consume.
+* addresses the issue of different timing require to produce work or consuming work
+

producer-consumer/pom.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0"?>
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.7.0</version>
+  </parent>
+  <artifactId>producer-consumer</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

producer-consumer/src/main/java/com/iluwatar/producer/consumer/App.java

@@ -0,0 +1,57 @@
+package com.iluwatar.producer.consumer;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Producer Consumer Design pattern is a classic concurrency or threading pattern which reduces
+ * coupling between Producer and Consumer by separating Identification of work with Execution of
+ * Work.
+ * <p>
+ * In producer consumer design pattern a shared queue is used to control the flow and this
+ * separation allows you to code producer and consumer separately. It also addresses the issue of
+ * different timing require to produce item or consuming item. by using producer consumer pattern
+ * both Producer and Consumer Thread can work with different speed.
+ * 
+ */
+public class App {
+
+  /**
+   * Program entry point
+   * 
+   * @param args command line args
+   */
+  public static void main(String[] args) {
+
+    ItemQueue queue = new ItemQueue();
+
+    ExecutorService executorService = Executors.newFixedThreadPool(5);
+    for (int i = 0; i < 2; i++) {
+
+      final Producer producer = new Producer("Producer_" + i, queue);
+      executorService.submit(() -> {
+        while (true) {
+          producer.produce();
+        }
+      });
+    };
+
+    for (int i = 0; i < 3; i++) {
+      final Consumer consumer = new Consumer("Consumer_" + i, queue);
+      executorService.submit(() -> {
+        while (true) {
+          consumer.consume();
+        }
+      });
+    }
+
+    executorService.shutdown();
+    try {
+      executorService.awaitTermination(10, TimeUnit.SECONDS);
+      executorService.shutdownNow();
+    } catch (InterruptedException e) {
+      System.out.println("Error waiting for ExecutorService shutdown");
+    }
+  }
+}

producer-consumer/src/main/java/com/iluwatar/producer/consumer/Consumer.java

@@ -0,0 +1,24 @@
+package com.iluwatar.producer.consumer;
+
+/**
+ * Class responsible for consume the {@link Item} produced by {@link Producer}
+ */
+public class Consumer {
+
+  private final ItemQueue queue;
+
+  private final String name;
+
+  public Consumer(String name, ItemQueue queue) {
+    this.name = name;
+    this.queue = queue;
+  }
+
+  public void consume() throws InterruptedException {
+
+    Item item = queue.take();
+    System.out.println(String.format("Consumer [%s] consume item [%s] produced by [%s]", name,
+        item.getId(), item.getProducer()));
+
+  }
+}

producer-consumer/src/main/java/com/iluwatar/producer/consumer/Item.java

@@ -0,0 +1,27 @@
+package com.iluwatar.producer.consumer;
+
+/**
+ * Class take part of an {@link Producer}-{@link Consumer} exchange.
+ */
+public class Item {
+
+  private String producer;
+
+  private int id;
+
+  public Item(String producer, int id) {
+    this.id = id;
+    this.producer = producer;
+  }
+
+  public int getId() {
+
+    return id;
+  }
+
+  public String getProducer() {
+
+    return producer;
+  }
+
+}

producer-consumer/src/main/java/com/iluwatar/producer/consumer/ItemQueue.java

@@ -0,0 +1,27 @@
+package com.iluwatar.producer.consumer;
+
+import java.util.concurrent.LinkedBlockingQueue;
+
+/**
+ * Class as a channel for {@link Producer}-{@link Consumer} exchange.
+ */
+public class ItemQueue {
+
+  private LinkedBlockingQueue<Item> queue;
+
+  public ItemQueue() {
+
+    queue = new LinkedBlockingQueue<Item>(5);
+  }
+
+  public void put(Item item) throws InterruptedException {
+
+    queue.put(item);
+  }
+
+  public Item take() throws InterruptedException {
+
+    return queue.take();
+  }
+
+}

producer-consumer/src/main/java/com/iluwatar/producer/consumer/Producer.java

@@ -0,0 +1,29 @@
+package com.iluwatar.producer.consumer;
+
+import java.util.Random;
+
+/**
+ * Class responsible for producing unit of work that can be expressed as {@link Item} and submitted
+ * to queue
+ */
+public class Producer {
+
+  private final ItemQueue queue;
+
+  private final String name;
+
+  private int itemId = 0;
+
+  public Producer(String name, ItemQueue queue) {
+    this.name = name;
+    this.queue = queue;
+  }
+
+  public void produce() throws InterruptedException {
+
+    Item item = new Item(name, itemId++);
+    queue.put(item);
+    Random random = new Random();
+    Thread.sleep(random.nextInt(2000));
+  }
+}

producer-consumer/src/test/java/com/iluwatar/poison/pill/AppTest.java

@@ -0,0 +1,20 @@
+package com.iluwatar.poison.pill;
+
+import org.junit.Test;
+
+import com.iluwatar.producer.consumer.App;
+
+/**
+ * 
+ * Application test
+ *
+ */
+public class AppTest {
+
+  @Test
+  public void test() throws Exception {
+    String[] args = {};
+    App.main(args);
+
+  }
+}