feat: Add comprehensive examples from multithreading and hashing lectures

src/main/java/lecture/multithreading/basics/JoinSimpleExample.java

@@ -0,0 +1,35 @@
+package lecture.multithreading.basics;
+
+
+class WorkerTask implements Runnable {
+    @Override
+    public void run() {
+        System.out.println("👷 Worker started...");
+        try {
+            Thread.sleep(10000); // Runs for 10 seconds
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        System.out.println("👷 The worker finished his work!");
+    }
+}
+
+public class JoinSimpleExample {
+    public static void main(String[] args) {
+        WorkerTask task = new WorkerTask();
+        Thread worker = new Thread(task);
+
+        worker.setName("Worker-Thread");
+        worker.start();
+
+        System.out.println("The main thread waits until the worker finishes...");
+
+        try {
+            worker.join(); // The main thread stops here until the worker finishes
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+
+        System.out.println("Main thread continues - now that the worker is finished!");
+    }
+}