Basic CRUD

Goal

In this mini project you will:

• Store user data in memory.

• Practice full CRUD: Create, Read, Update, Delete.

• Use Map, List, String, and simple I/O concepts together.

User.java

java
public class User {
    private int id;
    private String name;
    private String email;

    public User(int id, String name, String email) {
        this.id = id;
        this.name = name;
        this.email = email;
    }

    // Getters
    public int getId() { return id; }
    public String getName() { return name; }
    public String getEmail() { return email; }

    // Setters
    public void setName(String name) { this.name = name; }
    public void setEmail(String email) { this.email = email; }

    @Override
    public String toString() {
        return "User{" +
               "id=" + id +
               ", name='" + name + '\'' +
               ", email='" + email + '\'' +
               '}';
    }
}

UserRepository.java

java
import java.util.HashMap;
import java.util.Map;

public class UserRepository {
    private Map<Integer, User> storage = new HashMap<>();
    private int nextId = 1;

    // CREATE
    public User create(String name, String email) {
        User user = new User(nextId++, name, email);
        storage.put(user.getId(), user);
        return user;
    }

    // READ
    public User read(int id) {
        return storage.get(id);
    }

    // UPDATE
    public boolean update(int id, String newName, String newEmail) {
        User user = storage.get(id);
        if (user == null) return false;

        user.setName(newName);
        user.setEmail(newEmail);
        return true;
    }

    // DELETE
    public boolean delete(int id) {
        return storage.remove(id) != null;
    }

    // LIST ALL
    public void listAll() {
        for (User user : storage.values()) {
            System.out.println(user);
        }
    }
}

Main.java

java
public class Main {
    public static void main(String[] args) {
        UserRepository repo = new UserRepository();

        // CREATE users
        User u1 = repo.create("Alice", "alice@example.com");
        User u2 = repo.create("Bob", "bob@example.com");

        // LIST all users
        System.out.println("All users:");
        repo.listAll();

        // READ one user by ID
        System.out.println("Read ID 1: " + repo.read(1));

        // UPDATE user
        repo.update(1, "Alice Smith", "alice.smith@example.com");
        System.out.println("Updated ID 1: " + repo.read(1));

        // DELETE user
        repo.delete(2);
        System.out.println("After deletion:");
        repo.listAll();
    }
}