In my spring boot application. I created a class name Book and annotated that class with @Component annotation. Then I created a AppConfig class with @Configration annotation and in that class created a method name getBook() annotated with @Bean annotation which returns Book object.

So I was accepting a error as : required a single bean, but 2 were found when I will use @Autowird annotation to inject it but it not gave me any error and created two beans. So I observed that if I use the below code to inject it:

@Autowired
Book book;

It not gives me any error as here instance name is book.

But if I inject it as:

@Autowired
Book obj;

It gives me error as : required a single bean, but 2 were found

Can anyone tell me why it is like that.

1. Book class code:

@Component
public class Book {

void readBook() {
    System.out.println("reading book");
}

}

2. AppConfig class code:

@Configuration
public class AppConfig {

@Bean
Book getBook() {
    return new Book();
}

}

3. Main class code where I inject it and gets 2 bean found error:

@SpringBootApplication
public class IntroductionToSpringBootApplication implements CommandLineRunner {

@Autowired
Book obj;




public static void main(String[] args) {

    SpringApplication.run(IntroductionToSpringBootApplication.class, args);
}

@Override
public void run(String... args) throws Exception {      
}

}

4. Main class code where I inject it and gets no error:

@SpringBootApplication
public class IntroductionToSpringBootApplication implements CommandLineRunner {

@Autowired
Book book;




public static void main(String[] args) {

    SpringApplication.run(IntroductionToSpringBootApplication.class, args);
}

@Override
public void run(String... args) throws Exception {      
}

}