Added Observer

Author: NadavMozeson

src/BehavioralPatterns/Observer/Main.java

@@ -0,0 +1,21 @@
+package BehavioralPatterns.Observer;
+
+public class Main {
+    public static void main(String[] args) {
+        NewsAgency newsAgency = new NewsAgency();
+
+        Observer channel1 = new NewsChannel("Channel 1");
+        Observer channel2 = new NewsChannel("Channel 2");
+        Observer channel3 = new NewsChannel("Channel 3");
+
+        newsAgency.registerObserver(channel1);
+        newsAgency.registerObserver(channel2);
+        newsAgency.registerObserver(channel3);
+
+        newsAgency.publishNews("Breaking news!");
+
+        newsAgency.unregisterObserver(channel2);
+
+        newsAgency.publishNews("Another news!");
+    }
+}

src/BehavioralPatterns/Observer/NewsAgency.java

@@ -0,0 +1,30 @@
+package BehavioralPatterns.Observer;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class NewsAgency implements Subject {
+    private List<Observer> observers = new ArrayList<>();
+
+    @Override
+    public void registerObserver(Observer observer) {
+        observers.add(observer);
+    }
+
+    @Override
+    public void unregisterObserver(Observer observer) {
+        observers.remove(observer);
+    }
+
+    @Override
+    public void notifyObservers(String message) {
+        for (Observer observer : observers) {
+            observer.update(message);
+        }
+    }
+
+    public void publishNews(String news) {
+        System.out.println("Publishing news: " + news);
+        notifyObservers(news);
+    }
+}

src/BehavioralPatterns/Observer/NewsChannel.java

@@ -0,0 +1,14 @@
+package BehavioralPatterns.Observer;
+
+public class NewsChannel implements Observer {
+    private String channelName;
+
+    public NewsChannel(String channelName) {
+        this.channelName = channelName;
+    }
+
+    @Override
+    public void update(String message) {
+        System.out.println("Received news on " + channelName + ": " + message);
+    }
+}

src/BehavioralPatterns/Observer/Observer.java

@@ -0,0 +1,5 @@
+package BehavioralPatterns.Observer;
+
+public interface Observer {
+    void update(String message);
+}

src/BehavioralPatterns/Observer/Subject.java

@@ -0,0 +1,7 @@
+package BehavioralPatterns.Observer;
+
+public interface Subject {
+    void registerObserver(Observer observer);
+    void unregisterObserver(Observer observer);
+    void notifyObservers(String message);
+}