谁能解释我为什么会收到这个错误?
这是我使用双向链表实现的堆栈类:
import java.util.Iterator;
public class Stack<Item> implements Iterable<Item>{
private Node first;
private int N;
private class Node{
private Node next;
private Node prev;
private Item item;
}
public Iterator<Item> iterator(){
return new ReverseIterator<Item>();
}
private class ReverseIterator<Item> implements Iterator<Item>{
private Node x;
private ReverseIterator(){
if (first != null)
x = first.prev;
}
public boolean hasNext(){
return x != null;
}
public Item next(){
Item i = x.item;
x = x.prev;
return i;
}
public void remove(){
}
}
public void push(Item i){
if (isEmpty()){
first = new Node();
first.item = i;
first.next = first;
first.prev = first;
}
else{
Node x = new Node();
x.item = i;
x.next = first;
x.prev = first.prev;
first.prev.next = x;
first.prev = x;
}
N++;
}
public Item pop(){
assert !isEmpty() : "Stack is empty";
Item i = first.prev.item;
if (N == 1)
first = null;
else{
first.prev.prev.next = first;
first.prev = first.prev.prev;
}
N--;
return i;
}
public boolean isEmpty(){
return N == 0;
}
public int size(){
return N;
}
public static void main(String[] args){
}
}
Item i = x.item;
编译器说,预期的项目,找到的项目中存在错误。解决方案是替换ReverseIterator<Item>
为ReverseIterator
. 有人可以解释为什么我通过添加得到错误<Item>
吗?
谢谢