feat(generic-exceptions): add custom exception with error codes (non-generic example)

WHAT:
- Implemented a `CustomException2` class extending `Exception` to demonstrate how to enrich exceptions
  with additional contextual data (like error codes).
- Added `Main3` class with example usage where `throwException()` throws the custom exception, and the
  `main` method catches and prints the error code.

WHY:
- Standard Java exceptions often carry only a message, making it hard to attach structured metadata
  like error codes or identifiers.
- By extending `Exception` and adding fields (e.g., `errorCode`), we can provide more diagnostic
  information without relying on generics (since generic exceptions are restricted due to type erasure).

HOW:
- `CustomException2` includes:
  - `String message`: passed to `super(message)` for compatibility with existing exception handling.
  - `int errorCode`: a custom field to store a numeric identifier for the error.
  - `getErrorCode()`: accessor to retrieve the code during exception handling.
- In `Main3`:
  - `throwException()` method always throws a `CustomException2` with error code `1001`.
  - `main` catches the exception, extracts the error code, and prints it.

BENEFITS:
- Developers can differentiate between exceptions not only by type or message but also by structured
  fields (like error codes).
- Facilitates better logging, debugging, and mapping to user-friendly error responses in applications.

REAL-WORLD USE CASES:
- Banking/Finance: Attach transaction IDs or error codes for failed operations.
- REST APIs: Use error codes to map to HTTP status codes and provide consistent client responses.
- Enterprise apps: Internal error catalog where each error is assigned a unique code for support teams.

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

Author: Someshdiwan

Section24JavaGenerics/src/GenericExceptions/Main3.java

@@ -0,0 +1,29 @@
+package GenericExceptions;
+
+// Custom Exception without generics
+class CustomException2 extends Exception {
+    private final int errorCode;
+
+    public CustomException2(String message, int errorCode) {
+        super(message);
+        this.errorCode = errorCode;
+    }
+
+    public int getErrorCode() {
+        return errorCode;
+    }
+}
+
+public class Main3 {
+    public static void main(String[] args) {
+        try {
+            throwException();
+        } catch (CustomException2 e) {
+            System.out.println("Caught an exception with error code: " + e.getErrorCode());
+        }
+    }
+
+    public static void throwException() throws CustomException2 {
+        throw new CustomException2("Something went wrong", 1001);
+    }
+}