public class Feature {

   String name;

   String value;

}

public class InternalFeature extends Feature{

    Integer priority;

}

InternalFeature internalFeature = new InternalFeature();

internalFeature.setName("length");
internalFeature.setValue("56 Unit");
internalFeature.setPriority(1);

Feature feature = internalFeature;

InternalFeature(priority=1)