Custom Exceptions

In Java, you can create custom exceptions by extending the `Exception` class or one of its subclasses like `RuntimeException`. Custom exceptions are useful when you want to define your own exception types to represent specific error conditions in your application.

Syntax for creating a custom exception:

public class CustomException extends Exception {

    // Constructors, methods, and additional members can be defined here

}

Example of a custom exception:

public class InvalidAgeException extends Exception {

    public InvalidAgeException(String message) {

        super(message);

    }

}

public class AgeValidator {

    public static void validateAge(int age) throws InvalidAgeException {

        if (age < 0) {

            throw new InvalidAgeException("Age cannot be negative");

        }

        if (age < 18) {

            throw new InvalidAgeException("Must be at least 18 years old");

        }

        System.out.println("Age is valid");

    }

    public static void main(String[] args) {

        try {

            validateAge(20);

            validateAge(-5); // This will throw an InvalidAgeException

        } catch (InvalidAgeException e) {

            System.out.println("InvalidAgeException: " + e.getMessage());

        }

    }

}

In this example:

- We create a custom exception `InvalidAgeException` by extending the `Exception` class and providing a constructor to set the error message.

- The `validateAge` method throws `InvalidAgeException` if the age is negative or less than 18.

- In the `main` method, we catch `InvalidAgeException` and handle it appropriately.

Analogy:

Think of a custom exception as a specialized tool or equipment designed for a specific task. For example, in a carpentry workshop, if you encounter a particular type of material that requires a unique cutting technique, you might design a custom saw blade specifically for that material. Similarly, in Java, custom exceptions allow you to create specialized error-handling mechanisms tailored to specific error conditions in your application.