SpringBootLearning/springDataJpa/src/main/java/org/example/UserService.java

package org.example;

import java.util.List;

public interface UserService {
    public List<User> listUsers();

    public void saveUser(Long id, String name, int age);

    public void updateUser(Long id, String name, int age);

    public void deleteUser(Long id);

    public User getUserById(Long id);
}