第一版：增加add方法

package cn.zxg.collection; public class Node {
      Node previous;//上个节点     Node next;//下个节点     Object element;//自己的数据     public Node(Node previous,Node next,Object element){
          this.previous=previous;         this.next=next;         this.element=element;     }     public  Node(Object element){
          this.element=element;     } }

package cn.zxg.collection; /**  * 自定义一个链表，增加一个add方法  */ public class SxtLinkList {
      private Node first;     private  Node last;     private  int size;     public void add(Object obj){
          Node node=new Node(obj);         if(first==null){
              first=node;             last=node;         }else {
              node.previous=last;             node.next=null;             last.next=node;             last=node;         }     }     public String toString() {
          StringBuilder sb=new StringBuilder();         sb.append("[");         Node temp=first;         while (temp!=null){
              sb.append(temp.element+",");             temp=temp.next;         }         sb.setCharAt(sb.length()-1,']');         return sb.toString();     }     public static void main(String[] args) {
          SxtLinkList list=new SxtLinkList();         list.add("a");         list.add("b");         list.add("c");         System.out.println(list.toString());     } } 第二版、添加get方法，传入索引返回对应的内容