added ex S3

src/exercises/ex_s3/TestingAtomicLong.java

@@ -0,0 +1,32 @@
+package exercises.ex_s3;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class TestingAtomicLong {
+    public static String[] names = {
+        "Alice", "Bob", "Charlie", "Derek", "Emily",
+        "Fionna", "Greg", "Harry", "Isabella", "Julia"
+    };
+    public static void main(String[] args) throws InterruptedException {
+        List<AbstractTweet> tweets = new ArrayList<>();
+        AbstractTweet tweet1 = new Tweet("Alice", "Java is cool !");
+        AbstractTweet tweet2 = new AtomicTweet("Bob", "ISC is the best !");
+        tweets.add(tweet1);
+        tweets.add(tweet2);
+
+        Thread[] users = new Thread[10];
+
+        for (int i = 0; i < 10; i++) {
+            users[i] = new Thread(new User(names[i], tweets));
+            users[i].start();
+        }
+
+        for (int i = 0; i < 10; i++) {
+            users[i].join();
+        }
+
+        System.out.println(tweet1);
+        System.out.println(tweet2);
+    }
+}