为什么错了啊链表问题
package step3;
/**
* Created by zengpeng on 2017/12/25.
*/
public class MyLinkedList {
private Node first;//头结点，不存数据
private Node last;//指向链表的最后一个节点
private int size;
public MyLinkedList() {
size = 0;
first = new Node(0, null);
last = null;
}
/**
* 添加到链表尾部
*
* @param item
*/
public void add(int item) {
/********** Begin *********/
if(first == null){
first = new Node(item,null);
}else{
Node current = first;
while(current.next != null) {
current = current.next;
}
current.next = new Node(item,null);
}
size++;
/********** End *********/
}
/**
* 添加数据item到指定位置index
* index从0开始
* @param index
* @param item
*/
public void add(int index, int item) {
checkPosIndex(index);
/********** Begin *********/
Node previous;
Node current;
Node newnode = new Node(item,null);
if(index == 0){
newnode.next = first;
first = newnode;
size++;
}else{
current = first;
previous = null;
int j= 0;
while(current != null && j<index){
previous = current;
current = current.next;
j++;
}
if(j == index){
previous.next = newnode;
newnode.next = current;
size++;
}
}
/********** End *********/
}
/**
* 删除指定位置index处的元素并返回, index从0开始
* @param index
* @return
*/
public int remove(int index) {
checkPosIndex(index);
/********** Begin *********/
int oldValue = 0;
Node current = first;
if(index == 0){
oldValue = current.item;
first = current.next;
size--;
}else{
Node previous = null;
int j = 1;
while(current.next != null && j<=index){
previous = current;
current = current.next;
j++;
}
previous.next = current.next;
oldValue = current.item;
current = null;
size--;
}
return oldValue;
/********** End *********/
}
public int size() {
return size;
}
private void checkPosIndex(int index) {
if (index < 0 || index > size) {
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
}
}
//结点内部类
private static class Node {
int item;
Node next;
Node(int item, Node next) {
this.item = item;
this.next = next;
}
}
}