Bean annotations like @ManagedProperty and @PostConstruct doesn't work when manually instantiating the bean from another bean

Question

I instantiated a request bean from another request bean,

new LoginManager();

But the property which is annotated with @ManagedProperty doesn't get the value from the asked reference, only in case of instantiation through the above way. It just contains null, causing NPE later in code. Also @PostConstruct won't be invoked. Why is it so & how should I deal with this?

@ManagedBean(name = "loginManager")
@RequestScoped
public class LoginManager {

    private String userid;
    private String password;

    @ManagedProperty(value="#{currentSession}")
    private UserSessionManager userSession;

}

But userSession can't read from the session scoped bean when this bean was instantiated using: new LoginManager();

However I can read the value using FacesContext!