Adavance Exception Handling

Let’s go deeper and professional with multi-catch, try-with-resources, and best practices — these are must-knows if you’re aiming to become a top-tier Java coach or preparing students for real-world and enterprise-grade coding.

1️⃣ Multi-Catch (catch (Exception1 | Exception2 e))#

✅ Purpose:#

Handle multiple exception types with a single catch block, introduced in Java 7.

✅ Benefits:#

• Cleaner code (no duplication)
• Easier maintenance

📦 Example:#

public class MultiCatchExample {
    public static void main(String[] args) {
        try {
            String s = null;
            System.out.println(s.length()); // NullPointerException
            int x = 5 / 0;                  // ArithmeticException
        } catch (NullPointerException | ArithmeticException e) {
            System.out.println("Caught an exception: " + e.getClass().getSimpleName());
        }
    }
}

⚠️ Note: The exception types must not be parent-child (like IOException and FileNotFoundException) because it causes ambiguity.

2️⃣ Try-With-Resources (Automatic Resource Management)#

✅ Purpose:#

Auto-close resources like files, sockets, DB connections without needing finally.

Introduced in Java 7 and enhanced in Java 9.

✅ Works with classes that implement AutoCloseable or Closeable.#

📦 Example:#

import java.io.*;

public class TryWithResources {
    public static void main(String[] args) {
        try (BufferedReader br = new BufferedReader(new FileReader("test.txt"))) {
            System.out.println(br.readLine());
        } catch (IOException e) {
            System.out.println("IO Error: " + e.getMessage());
        }
    }
}

✅ Java 9+ Enhancement#

You can use an already declared variable (that is final or effectively final):

BufferedReader br = new BufferedReader(new FileReader("test.txt"));
try (br) {
    System.out.println(br.readLine());
}

3️⃣ Enterprise-Level Exception Handling: Best Practices#

Here’s what separates average developers from professionals:

✅ A. Don’t Swallow Exceptions#

Bad:

try {
    // risky code
} catch (Exception e) {
    // swallowed silently!
}

Good:

catch (Exception e) {
    logger.error("Exception occurred", e);
    throw e; // or wrap and throw
}

✅ B. Wrap Checked Exceptions (if appropriate)#

Use custom exceptions to hide implementation details.

try {
    // risky code
} catch (IOException e) {
    throw new DataAccessException("Failed to load data", e);
}

✅ C. Always Log Before Rethrowing#

catch (SQLException e) {
    logger.error("DB failure on loadUser()", e);
    throw e;
}

✅ D. Prefer Specific Exceptions#

catch (NumberFormatException e) {
    // Better than generic catch
}

✅ E. Use Custom Business Exceptions#

Make your code meaningful to the domain.

class InsufficientBalanceException extends RuntimeException {
    public InsufficientBalanceException(String message) {
        super(message);
    }
}

✅ F. Use Exception Hierarchy in Custom Exceptions#

class ApplicationException extends Exception {}
class ServiceException extends ApplicationException {}
class DataAccessException extends ApplicationException {}

This makes it easy to handle at different layers (UI, Service, DAO).

✅ G. Avoid Overusing Checked Exceptions#

Too many checked exceptions make APIs hard to use. Favor RuntimeException for programming errors.

🧠 Why This Matters#

✅ In real-world apps:

• You often need to log, rethrow, or convert exceptions
• You deal with IO, DB, and APIs — exception handling is everywhere
• Clean exception handling reflects clean system architecture

🏠 Homework for Students (Advanced)#

1. Create a file-reader method that uses try-with-resources to read and print a file line-by-line.

2. Write a program with a method parseInt(String s) that throws NumberFormatException, and use multi-catch to handle NumberFormatException and NullPointerException.

3. Create a layered architecture simulation:

   • DAO: throws SQLException
   • Service: catches it and throws DataAccessException
   • Controller: logs and shows friendly message

4. Create a custom exception hierarchy for a banking app:

   • BankingException
   • InsufficientFundsException
   • InvalidAccountException

Would you like to now dive into the Object Class Methods (equals(), hashCode(), toString()), or something like Enums, Annotations, or Wrapper classes vs primitives next?