UserDaoDb.java

import java.util.ArrayList;
import java.util.List;

public class UserDaoDb implements UserDao {

    private List<User> users;

    public UserDaoDb() {
        users = new ArrayList<User>();
        users.add(new User(1, "user1", "user1", "user1@test.com", "0624141145"));
        users.add(new User(2, "user2", "user2", "user2@test.com", "0652200241"));
        users.add(new User(3, "user3", "user3", "user3@test.com", "0600000025"));
        users.add(new User(4, "user4", "user4", "user4@test.com", "0600000026"));
        users.add(new User(5, "user5", "user5", "user5@test.com", "0652000014"));
    }

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

    public User select(int id) {

        for (User user : users) {
            if (user.getId() == id) {

                return user;
            }
        }

        return null;
    }

    public User select(String username, String password) {

        for (User user : users) {
            if (user.getUsername().equals(username) && user.getPassword().equals(password)) {

                return user;
            }
        }

        return null;
    }

    public void insert(User u) {

        users.add(u);
    }

    public void delete(User u) {

        users.remove(u);
    }

    public void update(User u) {

        if (users.contains(u)) {

            User user = select(u.getId());
            user = u;
            delete(user);
            insert(u);
        }
    }
}