Question

I have a superclass with its own nested class which is passed (/injected as provider) in the constructor.

Similarly i have a subclass with its own nested class which is injected (as a provider) in the constructor. Subclass.NestedClass extends Superclass.NestedClass.

public class SuperClass {
  @Inject SuperClass(Provider<SuperClass.Parameters> superParam) {
  }

  public class Parameters {
    int a;  
  }
}

public class Sub extends SuperClass {
  @Inject Sub(Provider<Sub.Parameters> subParam) {
     // Need to call super here with the appropriate superclass's provider
  }

  public class Parameters extends SuperClass.Parameters {
    int b;
  }
}

Is there a way i can convert the Provider of Sub.Parameters to SuperClass.Parameters’s provider so that i can call super(with that provider) in the constructor of Sub.

Answer 1

Java generics helped me here.

Solution:

public class SuperClass {
  // Constructor
  @Inject SuperClass(Provider<? extends SuperClass.Parameters> superParam) {
  }

  public class Parameters {
    int a;  
  }
}

public class Sub extends SuperClass {
  @Inject Sub(Provider<Sub.Parameters> subParam) {
     super(subParam);
  }

  public class Parameters extends SuperClass.Parameters {
    int b;
  }
}

Observe the difference in the super class constructor’s parameter “? extends”.