How can you create custom exceptions in Java ?

Definition

Custom exceptions in Java are user-defined exceptions created by extending the base Exception class (for checked exceptions) or RuntimeException class (for unchecked exceptions). These exceptions help handle specific error scenarios in a more descriptive and application-specific way.

Example

// Define a custom checked exception
class InvalidAgeException extends Exception {
    public InvalidAgeException(String message) {
        super(message);
    }
}

// Usage of the custom exception
public class CustomCheckedExceptionExample {
    public static void validateAge(int age) throws InvalidAgeException {
        if (age < 18) {
            throw new InvalidAgeException("Age must be 18 or older.");
        } else {
            System.out.println("Age is valid.");
        }
    }

    public static void main(String[] args) {
        try {
            validateAge(16); // This triggers the exception
        } catch (InvalidAgeException e) {
            System.out.println("Caught Exception: " + e.getMessage());
        }
    }
}

Output

Caught Exception: Age must be 18 or older.

Feature

• Custom Messages: Allow developers to define detailed error messages specific to the exception.
• Checked or Unchecked: Developers can choose whether the exception should be checked or unchecked based on the application’s needs.
• Inheritance: Custom exceptions integrate seamlessly with Java’s exception hierarchy.
• Centralized Error Handling: Simplifies debugging by categorizing specific types of errors.

Advantages

• Improved Readability: Provides descriptive and meaningful exception names, helping to understand the problem at a glance.
• Error-Specific Handling: Facilitates handling specific error scenarios distinct from generic exceptions.
• Encapsulation: Encapsulates error logic and conditions in one place, making the code modular and easier to maintain.
• Enhanced Debugging: Helps in debugging by clearly specifying the cause of the exception.
• Code Reusability: Custom exceptions can be reused across the application, promoting consistency in error handling.