added ex N

src/exercises/ex_n/News.java

@@ -0,0 +1,21 @@
+package exercises.ex_n;
+
+import java.time.LocalDateTime;
+
+public class News {
+    private String news;
+    private LocalDateTime date;
+
+    public News(String news) {
+        this.news = news;
+        this.date = LocalDateTime.now();
+    }
+
+    @Override
+    public String toString() {
+        return "News{" +
+        "news='" + news + '\'' +
+        ", date=" + date +
+        '}';
+    }
+}

src/exercises/ex_n/NewsFeed.java

@@ -0,0 +1,37 @@
+package exercises.ex_n;
+
+import java.util.Stack;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+public class NewsFeed {
+    private final Stack<News> newsStack = new Stack<>();
+    private final ReadWriteLock lock = new ReentrantReadWriteLock();
+    private final Lock writeLock = lock.writeLock();
+    private final Lock readLock = lock.readLock();
+
+    public NewsFeed() {
+
+    }
+
+    public void put(News news) {
+        try {
+            writeLock.lock();
+            newsStack.push(news);
+        } finally {
+            writeLock.unlock();
+        }
+    }
+
+    public News read() {
+        News news;
+        try {
+            readLock.lock();
+            news = newsStack.peek();
+        } finally {
+            readLock.unlock();
+        }
+        return news;
+    }
+}

src/exercises/ex_n/TestingReentrantReadWriteLock_News.java

@@ -0,0 +1,34 @@
+package exercises.ex_n;
+
+public class TestingReentrantReadWriteLock_News {
+    public static void main(String[] args) {
+        NewsFeed newsFeed = new NewsFeed();
+        newsFeed.put(new News("START OF NEWS"));
+
+        // Create one writing thread
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                for (int i=0;i<200;i++) {
+                    newsFeed.put(new News("News " + i));
+                }
+            }
+        }).start();
+
+        // Create several reading threads
+        for (int i=0; i<20;i++) {
+            new Thread((new Runnable() {
+                @Override
+                public void run() {
+                    for (int i=0;i<20;i++) {
+                        News news = newsFeed.read();
+                        if (news != null) {
+                            System.out.println("News read : "
+                            + newsFeed.read());
+                        }
+                    }
+                }
+            })).start();
+        }
+    }
+}