how does maping work in spring?

I have the following code:

import java.util.List;

import org.springframework.data.repository.Repository;

import net.javabeat.spring.data.domain.Book;

public interface BookNamedQueryRepositoryExample extends Repository<Book, Long> {
    // Query will be used from Named query defined at Entity class
    List<Book> findByPrice(long price);
}

I reviewed the entire project, and there is nowhere to implement the method, but it works when I do the test, what kind of magic is this? Why does it work if there is no implementation?