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 exception
class CustomException extends Exception {
    public CustomException(String message) {
        super(message); // Pass message to the superclass constructor
    }
}

// Example usage
public class CustomExceptionExample {
    // Method that throws the custom exception
    public static void checkNumber(int number) throws CustomException {
        if (number < 0) {
            throw new CustomException("Number cannot be negative: " + number);
        }
        System.out.println("Valid number: " + number);
    }

    public static void main(String[] args) {
        try {
            checkNumber(5);  // Valid case
            checkNumber(-3); // This will throw CustomException
        } catch (CustomException e) {
            System.out.println("Caught Exception: " + e.getMessage());
        }
    }
}

Output

Valid number: 5
Caught Exception: Number cannot be negative: -3

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.