我只是做一些练习,从我的书之一,我很好奇为什么我收到以下错误在日食:无法将节点<E>转换成节点<E>?
Type mismatch: cannot convert from type DoublyLinkedList.Node<E> to DoublyLinkedList.Node<E>
代码:
import java.util.Iterator;
import java.util.ListIterator;
import java.util.NoSuchElementException;
public class DoublyLinkedList<E extends Comparable<E>> implements Iterable<E>{
private int size = 0;
private Node<E> head;
private Node<E> tail;
/** Returns a list iterator object for the list at
* the specified index
*/
public DoublyLinkedList(){
}
private static class Node<E> {
Node<E> next = null;
Node<E> prev = null;
E data;
public Node(E dataItem){
data = dataItem;
}
public Node(E dataItem, Node<E> previous, Node<E> nextNode){
this(dataItem);
prev = previous;
next = nextNode;
}
}
private class MyListIter<E> implements ListIterator<E>{
private Node<E> lastReturned; // a link reference to the last item that was returned
private Node<E> nextItem; // a link reference to the next item in the list
/** The index of the current position */
private int index = 0;
public MyListIter(int pos){
if (pos < 0 || pos > size)
throw new IndexOutOfBoundsException("Invalid index: " + index);
lastReturned = null;
if (pos == size){
index = size;
nextItem = null;
} else { // otherwise we will start at the beginning of the list, and loop until the position in the argument
nextItem = head; // ERROR
for (index = 0; index < pos; index++){
nextItem = nextItem.next; // next item will always reference the list node that is called by the next method
}
}
}
@Override
public void add(E element) {
if (head == null){
Node<E> newNode = new Node<E>(element);
head = newNode; // ERROR
tail = head;
}
}
@Override
public boolean hasNext() {
return nextItem != null; // just checks to make sure there is a node following the current node
}
@Override
public boolean hasPrevious() {
return (nextItem == null && size != 0) || nextItem.prev != null;
}
@Override
public E next() {
if (!hasNext())
throw new NoSuchElementException("There is no node at that location");
lastReturned = nextItem;
nextItem = nextItem.next;
index++;
return lastReturned.data;
}
@Override
public int nextIndex() {
// TODO Auto-generated method stub
return 0;
}
@Override
public E previous() {
if (!hasPrevious())
throw new NoSuchElementException();
if (nextItem == null) // the iterator is at the end of the list
nextItem = tail; // therefore, the nextItem is at the tail, so the previous is the tail. ERROR HERE TOO
else
nextItem = nextItem.prev;
lastReturned = nextItem;
index--;
return lastReturned.data;
}
@Override
public int previousIndex() {
// TODO Auto-generated method stub
return 0;
}
@Override
public void remove() {
// TODO Auto-generated method stub
}
@Override
public void set(E arg0) {
// TODO Auto-generated method stub
}
}
@Override
public Iterator<E> iterator() {
// TODO Auto-generated method stub
return null;
}
}
我作了评论正是我在3个不同的位置得到错误。如果你能提供任何反馈,我会很感激。我的书没有解决它,我已经搜索过,并且看起来无法得到我正在寻找的答案。
+1好点关于'E extends Comparable super E>' –
哇。我永远不会知道。我认为这固定了一切。这本书写得很糟糕。我的印象是,如果DoublyLinkedList类型为,则该类别中的所有内容也应该是,使它们全部属于同一类型。但我猜它不是? –
TMGunter
@TMGunter:如果声明了一个不带'static'关键字的内部类,则该内部类的所有实例都必须属于包含类的特定_instance_。因此,它们自动访问为包含类声明的泛型类型(在这种情况下为'E')。我实际上不确定'Node'在这里是一个问题,因为它有'static'关键字,因此它是一个嵌套类,它不会继承'E'的定义。 'MyListIter'在这里可能是真正的问题,因为它继承了'E'的定义,但也声明了它自己的(冲突的)定义。 – ColinD