Use a static nested class with the same generic type as the enclosing class

Question

I have a setup like this:

public final class RequestContext<T extends Cache> {
     T roleSpecificCache;

     public static final class Spec implements Supplier<RequestContext> {
          private Spec() {

          }

          T roleSpecificCache; // << Getting error here
     }

     private RequestContext(Spec b) {
        this.roleSpecificCache = b.roleSpecificCache; // << I want to do this
     }
   }

However on the line T roleSpecificCache, I get the following error :

RequestContext.this cannot be referenced from a static context

I understand the reason why I'm getting this error (i.e. there's no direct link between the two classes), but don't know how to fix it. I want to to be able to do what I'm doing at the end.

Also, I cannot make Spec non-static (out of my hands).

score 2 · Accepted Answer · answered Jul 20 '18 at 01:39

You would need to parameterize Spec:

public final class RequestContext<T extends Cache> {
     T roleSpecificCache;

     public static final class Spec<T extends Cache>
     implements Supplier<RequestContext<T>> {
          private Spec() {
          }

          T roleSpecificCache;
     }

    private RequestContext(Spec<T> b) {
        this.roleSpecificCache = b.roleSpecificCache;
    }
}

It kind of seems like it should have been that way to begin with, because of the raw type argument to Supplier, which should be avoided.

Use a static nested class with the same generic type as the enclosing class

1 Answers1