Java实现双向链表(两个版本)

public class LinkedList<E> {
private Node head;
public LinkedList() {
}
public E getFirst(){
if(head==null){
return null;
}
return head.value;
}
public LinkedList<E> addFirst(E e){
head.pre=new Node(e, null, head);
head=head.pre;
return this;
}
public LinkedList<E> addNode(E e){
Node lst=head;
if(lst==null){
this.head=new Node(e, null, null);
return this;
}else{
while(true){
if(lst.next==null){
break;
}else{
lst=lst.next;
}
}
lst.next=new Node(e, lst, null);
return this;
}
}
public LinkedList<E> remove(E e){
Node lst=head;
if(lst==null){
throw new NullPointerException("the LinkedList is empty.");
}else{
while(true){
if(e.equals(lst.value)){
//移除这个元素
if(lst.pre!=null){
lst.pre.next=lst.next;
}
if(lst.next!=null){
lst.next.pre=lst.pre;
}
lst=null;
break;
}
lst=lst.next;
}
return this;
}
}
@Override
public String toString() {
StringBuffer buff=new StringBuffer("[");
Node lst=this.head;
while(lst!=null){
buff.append(lst.value+",");
lst=lst.next;
}
return buff.substring(0, buff.length()-1)+"]";
}
/**节点信息*/
private class Node{
public Node pre;
public E value;
public Node next;

public Node(E value,Node pre,Node next) {
this.value=value;
this.pre=pre;
this.next=next;
}
} 
}

public class LinkedList<E> {
private Node head;
private Node last;
public LinkedList() {
}
public E getFirst(){
if(head==null){
return null;
}
return head.value;
}
public E getLast(){
if(last==null){
return null;
}
return last.value;
}
public LinkedList<E> addFirst(E e){
head.pre=new Node(e, null, head);
head=head.pre;
return this;
}
public LinkedList<E> addNode(E e){
Node lst=last;
if(lst==null){//如果最后一个节点是空的则这个链表就是空的
this.last=new Node(e, null, null);
this.head=this.last;
return this;
}else{
while(true){
if(lst.next==null){//
break;
}else{
lst=lst.next;
}
}
lst.next=new Node(e, lst, null);
last=lst.next;
return this;
}
}
public LinkedList<E> remove(E e){
Node lst=head;
if(lst==null){
throw new NullPointerException("the LinkedList is empty.");
}else{
while(true){
if(e.equals(lst.value)){
//移除这个元素
if(lst.pre!=null){
lst.pre.next=lst.next;
}
if(lst.next!=null){
lst.next.pre=lst.pre;
}
lst=null;
break;
}
lst=lst.next;
}
return this;
}
}
@Override
public String toString() {
StringBuffer buff=new StringBuffer("[");
Node lst=this.head;
while(lst!=null){
buff.append(lst.value+",");
lst=lst.next;
}
return buff.substring(0, buff.length()-1)+"]";
}
/**节点信息*/
private class Node{
public Node pre;
public E value;
public Node next;

public Node(E value,Node pre,Node next) {
this.value=value;
this.pre=pre;
this.next=next;
}
}
}