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

below 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 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 node during creation of node.              */             private boolean lock;              lockablenode(t item, dblylinklist<t>.dlistnode<t> p,                     dblylinklist<t>.dlistnode<t> n) {                 super(item, p, n); // 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 above code, error:the constructor dblylinklist<t>.dlistnode<t>(t, dblylinklist<t>.dlistnode<t>, dblylinklist<t>.dlistnode<t>) undefined occurs @ line super(item, p, n)

this error resolved saying: class lockablenode<t> extends dblylinklist<t>.dlistnode<t>

how understand error? why got resolved?

you redeclaring type variable t in inner class. means within inner class, t of outer class hidden , cannot referred anymore.

since have non-static inner class, can remove type variable t there:

class dlistnode { ... } 

because inherits containing class (and mean variables same, anyway).