在接口方法中声明子类型捕获

Question

I am basically trying to achieve the following syntax (currently, doesn't compile). If someone can explain how to achieve this, I would appreciate it. Complicating matters is I have the 'add' method overloaded repeatedly

public interface Organization {
    Organization add(Hub hub);
}

public class JpaOrganization implements Organization {


    @OneToMany(mappedBy = "organization", cascade = CascadeType.ALL)
    private Set<JpaHub> hubs = new LinkedHashSet<>();


    @Override
    public JpaOrganization add(JpaHub hub) {
        hub.setOrganization(this);
        hubs.add(hub);
        return this;
    }
}

  public interface Hub {
    void setOrganization(Organization organization);
  }


public class JpaHub implements Hub {
    @Override
    public void setOrganization(JpaOrganization organization) {
        this.organization = organization;
    }
}

I am trying to do this to abstract a DAO layer away for an expected migration. So, all "JPA" implementations can assume they are dealing with JPA implementations, which is essential for all the reflection to work.

I need to capture the types but the syntax for this particular arrangement evades me.

I have tried something like:

<O extends Organization, H extends Hub> O foo(H hub);

implementation:

   @Override
    public JpaOrganization add(Hub hub) {
        return this;
    }

And this compiles but gives me a checked warning which indicates to me I might be doing something wrong. Based on what I am reading I am not sure I can do this without some warnings.

Answer 1

Define the type variables at class level:

public interface Organization<O extends Organization, H extends Hub> {
  O add(H hub);
}