feat(callable): demonstrate Callable with ExecutorService using invokeAll()

WHAT was added:
- Implemented `CallableMethod` class that:
  • Creates 3 Callable tasks (`callable1`, `callable2`, `callable3`) returning integers.
  • Uses `ExecutorService` with a fixed thread pool of size 3.
  • Submits all tasks at once via `invokeAll()`, ensuring all complete or timeout within 1000ms.
  • Collects `Future<Integer>` objects and retrieves results using `get()`.
- Gracefully shuts down the executor and prints confirmation ("Hello World").

WHY this matters:
- Demonstrates difference between `Runnable` and `Callable`:
  • `Runnable` → no return value.
  • `Callable<T>` → returns a result (via `Future<T>`).
- Shows how `invokeAll()` simplifies batch task submission and synchronization.
- Adds timeout support (`1000ms`) to prevent indefinite blocking if tasks take too long.

HINTS / NEXT STEPS:
- Experiment with `invokeAny()` to return the result of the first successfully completed task.
- Replace `System.out.println(f.get())` with proper aggregation or result processing.
- Explore behavior when one task exceeds the timeout (task gets cancelled).
- Compare with individual `submit(callable)` + `Future.get()` calls.

KEYWORDS:
callable invokeall future executorservice multithreading threadpool concurrency java.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Section19MultiThreading/ThreadPooling/src/ExecutorsFramework/CallableMethod.java renamed to Section19MultiThreading/ThreadPooling/RunnableVsCallable/src/CallableMethod.java

@@ -1,5 +1,3 @@
-package ExecutorsFramework;
-
 import java.util.Arrays;
 import java.util.List;
 import java.util.concurrent.*;
@@ -31,9 +29,7 @@ public static void main(String[] args) throws Exception {
         for (Future<Integer> f : futures) {
             System.out.println(f.get());
         }
-
         executorService.shutdown();
         System.out.println("Hello World");
     }
 }
-//InvokeALL() method done.