User-Defined Exception in Java

User-Defined Exception in Java

📌What is a User-Defined Exception in Java?

In Java, a user-defined exception (also known as a custom exception) is a special type of exception that developers create to handle specific error conditions that are not covered by built-in exceptions. These exceptions are created by extending the Exception class and using the throw keyword to trigger them when needed.

📌Why Use User-Defined Exceptions?

Creating custom exceptions provides several benefits, including:

• Handling Specific Application Errors: Standard exceptions like NullPointerException or ArrayIndexOutOfBoundsException may not always cover the errors in your application. User-defined exceptions help address specific issues.
• Improving Code Readability: By defining meaningful exception names, developers can easily understand and debug errors.
• Enhancing Code Maintainability: With custom exceptions, you can centralize error-handling logic, making future updates easier.
• Following Best Practices: Custom exceptions help maintain clean and structured error-handling mechanisms in Java applications.

📌How to Create a User-Defined Exception in Java:

📌Step 1: Define a Custom Exception Class:

To create a user-defined exception, extend the Exception class and override the toString() method for a meaningful error message.

java

// Custom Exception Class
class InvalidAgeException extends Exception {
    private int age;
    
    // Constructor
    public InvalidAgeException(int age) {
        this.age = age;
    }
    
    // Custom error message
    public String toString() {
        return "InvalidAgeException: Age " + age + " is not valid.";
    }
}

📌Step 2: Use the Custom Exception in Your Code:

Now, use the custom exception in a program and handle it using try-catch.

java

public class CustomExceptionDemo {
    static void checkAge(int age) throws InvalidAgeException {
        if (age < 18) {
            throw new InvalidAgeException(age); // Throw custom exception
        } else {
            System.out.println("Access granted. Age: " + age);
        }
    }

    public static void main(String[] args) {
        try {
            checkAge(16); // This will trigger the custom exception
        } catch (InvalidAgeException e) {
            System.out.println(e);
        }
    }
}

Expected Output:

vbnet

InvalidAgeException: Age 16 is not valid.

📌Best Practices for Using User-Defined Exceptions:

1. Use Meaningful Names: Name your exceptions based on the error scenario (e.g., InvalidTransactionException).
2. Extend the Right Class: Use Exception for checked exceptions and RuntimeException for unchecked exceptions.
3. Provide Constructors: Allow custom messages and error codes for better debugging.
4. Log Exceptions: Always log exceptions to identify issues efficiently.
5. Avoid Overuse: Use custom exceptions only when necessary to prevent unnecessary complexity.

📌Conclusion:

User-defined exceptions in Java allow developers to create meaningful error messages, improve code readability, and enhance maintainability. By defining and handling custom exceptions properly, Java applications become more robust and user-friendly.