如何在这段代码中继承父类的内部类？ [英] How to inherit parent's inner class in this code?

问题描述

以下是父类 DblyLinkList

  package JavaCollections.list ; 
 
 import java.util.Iterator; 
 import java.util.NoSuchElementException; 
 
 public class DblyLinkList< T>实现Iterable< T> {
 
 class DListNode< T> {
 
私人T项; 
私人DListNode< T>上一张; 
私人DListNode< T>下一个; 
 
 DListNode（T item，DListNode< T> p，DListNode< T> n）{
 this.item = item; 
 this.prev = p; 
 this.next = n; 
} 
 
 
} 
 ..... 
} 
  

下面是派生类 LockableList ，

  package JavaCollections.list; 
 
 import JavaCollections.list.DblyLinkList.DListNode; 
 
公共类LockableList< T>扩展DblyLinkList< T> {
 
 class LockableNode< T>扩展DblyLinkList< T> .DListNode< T> {
 
 / ** 
 *在创建节点时锁定节点。 
 * / 
私人布尔锁定; 
 
 LockableNode（T item，DblyLinkList< T> .DListNode< T> p，
 DblyLinkList< T> .DListNode< T> n） N）; //这不起作用
 this.lock = false; 
} 
 
} 
 
 LockableNode< T> newNode（T item，DListNode< T> prev，DListNode< T> next）{
返回新的LockableNode（item，prev，next）; 
} 
 
 public LockableList（）{
 this.sentinel = this.newNode（null，this.sentinel，this.sentinel）; 
} 
 
 
 ..... 
} 
  

如果 class LockableNode< T>在以上代码中扩展DListNode ， error ：构造函数DblyLinkList< T> .DListNode< T>（T，DblyLinkList< T> （item，p，n） 处出现未定义的 .DListNode< T> ;, DblyLinkList< T> .DListNode< / p>

解决这个错误的方法是： class LockableNode< T>扩展DblyLinkList< T> .DListNode< T>

我如何理解这个错误？为什么它得到解决？

解决方案

您将重新声明类型变量 T 在内部阶层。这意味着在内部类中，外部类的 T 是隐藏的，不能再被引用。

由于你有一个非静态的内部类，你可以在这里删除类型变量 T ：

  class DListNode {...} 
  

因为它从包含类（也许你的意思是变量是相同的，无论如何）。

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?

解决方案

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).

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