added ex A

src/exercicses/ex_a/HelloRunnable.java

@@ -0,0 +1,8 @@
+package exercicses.ex_a;
+
+public class HelloRunnable implements Runnable {
+    @Override
+    public void run() {
+        System.out.println("Hello from a class implementing the Runnable interface");
+    }
+}

src/exercicses/ex_a/HelloThread.java

@@ -0,0 +1,8 @@
+package exercicses.ex_a;
+
+public class HelloThread extends Thread {
+    @Override
+    public void run() {
+        System.out.println("Hello from a class extending the Thread class");
+    }
+}

src/exercicses/ex_a/TestingSimpleThreads.java

@@ -0,0 +1,8 @@
+package exercicses.ex_a;
+
+public class TestingSimpleThreads {
+    public static void main(String[] args) {
+        new HelloThread().start();
+        new Thread(new HelloRunnable()).start();
+    }
+}