refactor(banking-demo): introduce DemoApplication orchestrator and add controlled lifecycle management

- Replace DemoFactory with DemoApplication to centralize system setup, execution, and shutdown
- Move ExecutorService and ScheduledExecutorService lifecycle management into application layer
- Ensure proper shutdown sequence for worker and monitoring threads
- Simplify Main class to a minimal entry-point wrapper
- Improve clarity of execution flow: build → run → shutdown
- Prevent resource leakage by explicitly awaiting termination of thread pools

src/main/java/dev/banking/DemoApplication.java

@@ -0,0 +1,108 @@
+package dev.banking;
+
+import dev.banking.model.*;
+import dev.banking.monitor.LiveMonitor;
+import dev.banking.processor.TransactionProcessor;
+import dev.banking.service.BankingSystem;
+
+import java.util.*;
+import java.util.concurrent.*;
+
+/**
+ * DemoApplication is responsible for:
+ * - Building the system
+ * - Running the simulation
+ * - Managing lifecycle (threads, schedulers)
+ *
+ * This class replaces DemoFactory as a full runner.
+ */
+public final class DemoApplication {
+
+    private DemoApplication() {
+    }
+
+    public static void run() {
+
+        System.out.println("Initializing Banking Simulation...\n");
+
+        /*
+         * 1. Create bank accounts
+         */
+        BankAccount acc1 = new BankAccount(1, 1000);
+        BankAccount acc2 = new BankAccount(2, 2000);
+        BankAccount acc3 = new BankAccount(3, 1500);
+
+        Map<Integer, BankAccount> accounts = new HashMap<>();
+        accounts.put(1, acc1);
+        accounts.put(2, acc2);
+        accounts.put(3, acc3);
+
+        /*
+         * 2. Create transactions
+         */
+        List<Transaction> transactions = List.of(
+                new DepositTransaction(1, 200),
+                new WithdrawTransaction(2, 300),
+                new TransferTransaction(1, 2, 150),
+                new TransferTransaction(2, 3, 400),
+                new DepositTransaction(3, 500),
+                new WithdrawTransaction(1, 100),
+                new TransferTransaction(3, 1, 250)
+        );
+
+        /*
+         * 3. Thread pool (workers)
+         */
+        ExecutorService executor = Executors.newFixedThreadPool(4);
+
+        /*
+         * 4. Processor
+         */
+        TransactionProcessor processor = new TransactionProcessor(accounts);
+
+        /*
+         * 5. Banking system
+         */
+        BankingSystem bankingSystem = new BankingSystem(executor, processor);
+
+        /*
+         * 6. Live monitor (UI simulation)
+         */
+        LiveMonitor monitor = new LiveMonitor();
+
+        ScheduledExecutorService monitorExecutor = Executors.newSingleThreadScheduledExecutor();
+
+        monitorExecutor.scheduleAtFixedRate(() -> {
+            monitor.update(accounts.values());
+            System.out.println("----------------------");
+        }, 0, 1, TimeUnit.SECONDS);
+
+        /*
+         * 7. Run simulation
+         */
+        bankingSystem.processTransactions(transactions);
+
+        /*
+         * 8. Shutdown / lifecycle management
+         */
+        shutdown(executor, monitorExecutor);
+
+        System.out.println("\nSimulation completed.");
+    }
+
+    private static void shutdown(
+            ExecutorService executor,
+            ScheduledExecutorService monitorExecutor
+    ) {
+        try {
+            executor.shutdown();
+            executor.awaitTermination(5, TimeUnit.SECONDS);
+
+            monitorExecutor.shutdown();
+            monitorExecutor.awaitTermination(5, TimeUnit.SECONDS);
+
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+        }
+    }
+}

src/main/java/dev/banking/DemoFactory.java

@@ -1,55 +0,0 @@
-package dev.banking;
-
-import dev.banking.service.BankingSystem;
-
-/**
- * Creates a ready-to-run demonstration environment.
- *
- * Students do not need to modify this class.
- */
-public final class DemoFactory {
-
-    private DemoFactory() {
-    }
-
-    /**
-     * Builds a fully configured banking simulation system.
-     *
-     * This includes:
-     * - Bank accounts
-     * - Transaction stream generator / loader
-     * - ExecutorService (thread pool)
-     * - Transaction processor
-     * - Live monitoring system
-     *
-     * @return configured BankingSystem instance
-     */
-    public static BankingSystem createDemoSystem() {
-
-        /*
-         * TODO (Instructor Implementation Only)
-         *
-         * Example responsibilities:
-         *
-         * 1. Create bank accounts:
-         *    - Account(1, 1000)
-         *    - Account(2, 2000)
-         *    - Account(3, 1500)
-         *
-         * 2. Create transaction list or stream
-         *
-         * 3. Initialize ExecutorService:
-         *    Executors.newFixedThreadPool(n)
-         *
-         * 4. Create TransactionProcessor
-         *
-         * 5. Create BankingSystem and inject dependencies
-         *
-         * 6. Attach LiveMonitor (optional)
-         */
-
-        throw new UnsupportedOperationException(
-                "Instructor implementation required."
-        );
-    }
-}

src/main/java/dev/banking/Main.java

@@ -1,17 +1,11 @@
 package dev.banking;
 
-import dev.banking.service.BankingSystem;
-import dev.banking.DemoFactory;
-
 /**
  * Entry point of the application.
  *
- * This class is provided for demonstration purposes only.
- *
  * IMPORTANT:
- * - Do NOT modify this file.
- * - This file is NOT used during grading.
- * - All grading is performed through the provided JUnit tests.
+ * - Do NOT modify this file in student assignment.
+ * - This is only a wrapper for running the demo.
  */
 public final class Main {
 
@@ -22,25 +16,19 @@ public final class Main {
 
         System.out.println("=================================");
         System.out.println(" Advanced Banking System");
-        System.out.println("=================================");
+        System.out.println("=================================\n");
 
         try {
 
-            BankingSystem bankingSystem =
-                    DemoFactory.createDemoSystem();
-
-            System.out.println("System initialized...");
-            System.out.println("Running simulation with concurrent workers...\n");
-
-//            bankingSystem.start();
+            DemoApplication.run();
 
             System.out.println("\n=================================");
-            System.out.println("Simulation completed successfully.");
+            System.out.println(" System finished successfully ");
             System.out.println("=================================");
 
         } catch (Exception e) {
 
-            System.err.println("\nUnexpected error occurred:");
+            System.err.println("Unexpected error occurred:");
             e.printStackTrace();
         }
     }

src/main/java/dev/banking/model/BankAccount.java

@@ -31,7 +31,7 @@ public class BankAccount {
      * TODO
      * Implement a thread-safe deposit operation.
      */
-    public void deposit(int amount) {
+    public void deposit(long amount) {
         throw new UnsupportedOperationException();
     }
 
@@ -39,7 +39,7 @@ public class BankAccount {
      * TODO
      * Implement a thread-safe withdrawal operation.
      */
-    public void withdraw(int amount) {
+    public void withdraw(long amount) {
         throw new UnsupportedOperationException();
     }
 
@@ -47,7 +47,7 @@ public class BankAccount {
      * TODO
      * Implement an atomic and deadlock-free transfer.
      */
-    public void transfer(BankAccount target, int amount) {
+    public void transfer(BankAccount target, long amount) {
         throw new UnsupportedOperationException();
     }
 }

src/main/java/dev/banking/model/TransactionType.java

@@ -1,7 +0,0 @@
-package dev.banking.model;
-
-public enum TransactionType {
-    DEPOSIT,
-    WITHDRAW,
-    TRANSFER
-}