Recap - Validated User

Part of the Object Oriented Programming section of Coddy's Java journey — lesson 63 of 87.

Challenge

Easy

Let's build a complete user registration system that validates input data and uses custom exceptions to communicate exactly what went wrong! You'll combine everything from this chapter: custom checked and unchecked exceptions, the exception hierarchy, and try-with-resources with an auto-closeable validator.

You'll organize your code across five files:

ValidationException.java: Create a checked exception that serves as the base for all validation errors. This exception should extend Exception and include a constructor that accepts a message.
InvalidUsernameException.java: Create a checked exception for username validation failures. This should extend your ValidationException class, creating a small exception hierarchy. Include a constructor that accepts a message and passes it to the parent.
InvalidAgeException.java: Create an unchecked exception for age-related errors (like negative ages, which represent programming errors). This should extend RuntimeException with a constructor that accepts a message.
UserValidator.java: Create a class that implements AutoCloseable to simulate a validation session that should be properly closed. Your validator should:
Print Validator session started in the constructor.

Have a validateUsername(String username) method that throws InvalidUsernameException if the username is null, empty, or less than 3 characters (with message "Username must be at least 3 characters"). Otherwise, print Username '[username]' is valid.

Have a validateAge(int age) method that throws InvalidAgeException if age is negative (with message "Age cannot be negative: [age]"). If age is less than 13, throw ValidationException with message "Must be at least 13 years old". Otherwise, print Age [age] is valid.

Implement close() to print Validator session closed.
Main.java: Bring your validation system together! You'll receive two inputs: a username (String) and an age (integer).
Use try-with-resources to create a UserValidator. Inside the try block, first validate the username, then validate the age. If both pass, print User registration successful!

Catch InvalidUsernameException and print Username error: [message]. Catch InvalidAgeException and print Age error: [message]. Catch ValidationException (the parent) and print Validation error: [message].

The validator should automatically close regardless of whether validation succeeds or fails!

You will receive two inputs in order: username (String) and age (integer).

This challenge brings together the entire chapter: you'll build an exception hierarchy with ValidationException as a parent, use both checked and unchecked exceptions appropriately, and ensure your validator resource is always cleaned up with try-with-resources. Notice how catching the parent ValidationException after its child InvalidUsernameException lets you handle specific cases first while still catching other validation errors!

Try it yourself

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        
        // Read inputs
        String username = scanner.nextLine();
        int age = scanner.nextInt();
        
        // TODO: Use try-with-resources to create a UserValidator
        // Inside the try block:
        //   1. Validate the username
        //   2. Validate the age
        //   3. If both pass, print "User registration successful!"
        
        // TODO: Catch InvalidUsernameException and print "Username error: [message]"
        
        // TODO: Catch InvalidAgeException and print "Age error: [message]"
        
        // TODO: Catch ValidationException (parent) and print "Validation error: [message]"
        
        // Note: The validator should automatically close regardless of success or failure!
    }
}