feat: Add comprehensive examples from multithreading and hashing lectures

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

@@ -0,0 +1,31 @@
+package lecture.multithreading.basics;
+
+public class IsAliveExample {
+    public static void main(String[] args) throws InterruptedException {
+        Thread worker = new Thread(new Runnable() {
+            @Override
+            public void run() {
+                System.out.println("👷 Worker started...");
+                try {
+                    Thread.sleep(15000); // Runs for 15 seconds
+                } catch (InterruptedException e) {
+                    e.printStackTrace();
+                }
+                System.out.println("👷 The worker is done!");
+            }
+        });
+
+        System.out.println("before start: " + worker.isAlive()); // false
+
+        worker.start();
+
+        System.out.println("Immediately after start: " + worker.isAlive()); // true
+
+        Thread.sleep(1000); // We wait 1 second
+        System.out.println("After 1 second: " + worker.isAlive()); // true (still works)
+
+        worker.join(); // We wait for the worker to finish
+
+        System.out.println("After completion of work: " + worker.isAlive()); // false
+    }
+}