Review Core Java Concepts

Review Core Java Concepts

Why Review Matters

Before jumping into web, it’s important to review and connect the core Java pieces you learned:

• Classes & Objects → how web requests map to Java classes.

• Methods → how endpoints call business logic.

• Collections → how you handle request data, query results.

• Exceptions → how you handle bad input or server errors.

• File I/O & DateTime → logging, reading configs, timestamps.

Everything you coded so far is not isolated — it’s exactly the foundation that real web backends use.

✅ Key Bridge:

• Your CRUD logic becomes a service in web.

• Your classes become DTOs (Data Transfer Objects).

• Your collections become in-memory DB → later a real DB.

• Your Main method becomes an HTTP server listening for requests.

Mini Lab: Concept Mapping

java
// Basic CRUD class reused in web
public class User {
    private int id;
    private String name;
    private String email;

    // getters/setters
}

// Service layer logic
public class UserService {
    private List<User> users = new ArrayList<>();

    public void addUser(String name, String email) {
        users.add(new User(users.size() + 1, name, email));
    }

    public List<User> getAllUsers() {
        return users;
    }
}

In a web app:

• You don’t System.out.println the data.

• You return it as JSON to the browser.

• You receive user input as HTTP POST data, not Scanner.