feat: implement TransactionProcessor with type-based dispatch for all transaction operations

src/main/java/dev/banking/processor/TransactionProcessor.java

@@ -16,29 +16,36 @@ public class TransactionProcessor {
 
     public void process(Transaction tx) {
 
-        BankAccount source =
-                accounts.get(tx.getSourceAccountId());
+        if (tx instanceof DepositTransaction deposit) {
 
-        switch (tx.getType()) {
+            BankAccount account = accounts.get(deposit.getAccountId());
 
-            case DEPOSIT -> {
-                source.deposit(tx.getAmount());
-            }
+            account.deposit(deposit.getAmount());
+        }
 
-            case WITHDRAW -> {
-                source.withdraw(tx.getAmount());
-            }
+        else if (tx instanceof WithdrawTransaction withdraw) {
 
-            case TRANSFER -> {
+            BankAccount account = accounts.get(withdraw.getAccountId());
 
-                BankAccount target =
-                        accounts.get(tx.getTargetAccountId());
+            account.withdraw(withdraw.getAmount());
+        }
 
-                source.transfer(
-                        target,
-                        tx.getAmount()
-                );
-            }
+        else if (tx instanceof TransferTransaction transfer) {
+
+            BankAccount source = accounts.get(transfer.getSourceAccountId());
+
+            BankAccount target = accounts.get(transfer.getTargetAccountId());
+
+            source.transfer(
+                    target,
+                    transfer.getAmount()
+            );
+        }
+
+        else {
+            throw new IllegalArgumentException(
+                    "Unknown transaction type: " + tx.getClass()
+            );
         }
     }
 }