How do constructor calls with @Autowired work?

Question

I\'m learning the Spring Boot framework and I want to understand how the @Autowired annotation works. I know that in Spring Boot we have a context, and inside that

Answer 1

Long story short

Spring will use the default constructor (the no-args constructor) to construct the components. In your example

@Service
public class MyService {

public MyService() {
   // do something
}
}

the constructor will be called and the // do something will be called.

However, keep in mind that if you added a non-default constructor to the class(a constructor with arguments) then the compiler will not generate a default constructor for you and in this case, spring will fail to instantiate your MyService

For example

  @Service
    public class MyService {

    public MyService(String var) {
       // do something
    }
    }

will throw an exception Parameter 0 of constructor in com.example.MyService required a bean of type 'java.lang.String' that could not be found.