How to inherit parent's inner class in this code?

Question

Below is the parent class DblyLinkList

package JavaCollections.list;

import java.util.Iterator;
import java.util.NoSuchElementException;

public class DblyLinkList<T> implements Iterable<T>{

    class DListNode<T> {

        private T item;
        private DListNode<T> prev;
        private DListNode<T> next;

        DListNode(T item, DListNode<T> p, DListNode<T> n) {
            this.item = item;
            this.prev = p;
            this.next = n;
        }


    }
.....
}

Below is the derived class LockableList,

  package JavaCollections.list;

    import JavaCollections.list.DblyLinkList.DListNode;

    public class LockableList<T> extends DblyLinkList<T> {

        class LockableNode<T> extends DblyLinkList<T>.DListNode<T> {

            /**
             * lock the node during creation of a node.
             */
            private boolean lock;

            LockableNode(T item, DblyLinkList<T>.DListNode<T> p,
                    DblyLinkList<T>.DListNode<T> n) {
                super(item, p, n); // this does not work
                this.lock = false;
            }

        }

        LockableNode<T> newNode(T item, DListNode<T> prev, DListNode<T> next) {
            return new LockableNode(item, prev, next);
        }

        public LockableList() {
            this.sentinel = this.newNode(null, this.sentinel, this.sentinel);
        }


    .....
 }

If class LockableNode<T> extends DListNode<T> in the above code, error:The constructor DblyLinkList<T>.DListNode<T>(T, DblyLinkList<T>.DListNode<T>, DblyLinkList<T>.DListNode<T>) is undefined occurs at line super(item, p, n)

This error is resolved by saying: class LockableNode<T> extends DblyLinkList<T>.DListNode<T>

How do I understand this error? Why it got resolved?

Answer 1

You are redeclaring the type variable T in the inner class. That means that within the inner class, the T of the outer class is hidden and cannot be referred to anymore.

Since you have a non-static inner class, you can just remove the type variable T there:

class DListNode { ... }

because it inherits it from the containing class (and probably you mean that the variables are the same, anyway).