BAEL-1497 (#3568)

core-java/src/main/java/com/baeldung/designpatterns/observer/Channel.java

@@ -0,0 +1,5 @@
+package com.baeldung.designpatterns.observer;
+
+public interface Channel {
+    public void update(Object o);
+}

core-java/src/main/java/com/baeldung/designpatterns/observer/NewsAgency.java

@@ -0,0 +1,24 @@
+package com.baeldung.designpatterns.observer;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class NewsAgency {
+    private String news;
+    private List<Channel> channels = new ArrayList<>();
+
+    public void addObserver(Channel channel) {
+        this.channels.add(channel);
+    }
+
+    public void removeObserver(Channel channel) {
+        this.channels.remove(channel);
+    }
+
+    public void setNews(String news) {
+        this.news = news;
+        for (Channel channel : this.channels) {
+            channel.update(this.news);
+        }
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/observer/NewsChannel.java

@@ -0,0 +1,20 @@
+package com.baeldung.designpatterns.observer;
+
+public class NewsChannel implements Channel {
+
+    private String news;
+
+    @Override
+    public void update(Object news) {
+        this.setNews((String) news);
+    }
+
+    public String getNews() {
+        return news;
+    }
+
+    public void setNews(String news) {
+        this.news = news;
+    }
+
+}

core-java/src/main/java/com/baeldung/designpatterns/observer/ONewsAgency.java

@@ -0,0 +1,13 @@
+package com.baeldung.designpatterns.observer;
+
+import java.util.Observable;
+
+public class ONewsAgency extends Observable {
+    private String news;
+
+    public void setNews(String news) {
+        this.news = news;
+        setChanged();
+        notifyObservers(news);
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/observer/ONewsChannel.java

@@ -0,0 +1,22 @@
+package com.baeldung.designpatterns.observer;
+
+import java.util.Observable;
+import java.util.Observer;
+
+public class ONewsChannel implements Observer {
+
+    private String news;
+
+    @Override
+    public void update(Observable o, Object news) {
+        this.setNews((String) news);
+    }
+
+    public String getNews() {
+        return news;
+    }
+
+    public void setNews(String news) {
+        this.news = news;
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/observer/PCLNewsAgency.java

@@ -0,0 +1,28 @@
+package com.baeldung.designpatterns.observer;
+
+import java.beans.PropertyChangeListener;
+import java.beans.PropertyChangeSupport;
+
+public class PCLNewsAgency {
+    private String news;
+
+    private PropertyChangeSupport support;
+
+    public PCLNewsAgency() {
+        support = new PropertyChangeSupport(this);
+    }
+
+    public void addPropertyChangeListener(PropertyChangeListener pcl) {
+        support.addPropertyChangeListener(pcl);
+    }
+
+    public void removePropertyChangeListener(PropertyChangeListener pcl) {
+        support.removePropertyChangeListener(pcl);
+    }
+
+    public void setNews(String value) {
+        support.firePropertyChange("news", this.news, value);
+        this.news = value;
+
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/observer/PCLNewsChannel.java

@@ -0,0 +1,21 @@
+package com.baeldung.designpatterns.observer;
+
+import java.beans.PropertyChangeEvent;
+import java.beans.PropertyChangeListener;
+
+public class PCLNewsChannel implements PropertyChangeListener {
+
+    private String news;
+
+    public void propertyChange(PropertyChangeEvent evt) {
+        this.setNews((String) evt.getNewValue());
+    }
+
+    public String getNews() {
+        return news;
+    }
+
+    public void setNews(String news) {
+        this.news = news;
+    }
+}

core-java/src/test/java/com/baeldung/designpatterns/observer/ObserverIntegrationTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.designpatterns.observer;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+import com.baeldung.designpatterns.observer.NewsAgency;
+import com.baeldung.designpatterns.observer.NewsChannel;
+
+public class ObserverIntegrationTest {
+
+    @Test
+    public void whenChangingNewsAgencyState_thenNewsChannelNotified() {
+
+        NewsAgency observable = new NewsAgency();
+        NewsChannel observer = new NewsChannel();
+
+        observable.addObserver(observer);
+
+        observable.setNews("news");
+        assertEquals(observer.getNews(), "news");
+    }
+
+    @Test
+    public void whenChangingONewsAgencyState_thenONewsChannelNotified() {
+
+        ONewsAgency observable = new ONewsAgency();
+        ONewsChannel observer = new ONewsChannel();
+
+        observable.addObserver(observer);
+
+        observable.setNews("news");
+        assertEquals(observer.getNews(), "news");
+    }
+
+    @Test
+    public void whenChangingPCLNewsAgencyState_thenONewsChannelNotified() {
+
+        PCLNewsAgency observable = new PCLNewsAgency();
+        PCLNewsChannel observer = new PCLNewsChannel();
+
+        observable.addPropertyChangeListener(observer);
+
+        observable.setNews("news");
+        assertEquals(observer.getNews(), "news");
+    }
+}