优点：易于插入和删除，内存利用率高
缺点：和数组相比需要更多内存，遍历困难，反向遍历更难。（双链表内存消耗更大）
创建节点 class Node {
private int data;
private Node next;
public Node(int data) {
this.data = data;
this.next = next;
}
}
链表的增删改查
(20条消息) Java 实现单链表的基本操作_近未来-CSDN博客_java链表的基本操作https://blog.csdn.net/qq_40933663/article/details/93497914?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522164466592116780255235165%2522%252C%2522scm%2522%253A%252220140713.130102334..%2522%257D&request_id=164466592116780255235165&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~sobaiduend~default-1-93497914.pc_search_result_positive&utm_term=%E9%93%BE%E8%A1%A8%E7%9A%84%E5%9F%BA%E6%9C%AC%E6%93%8D%E4%BD%9Cjava&spm=1018.2226.3001.4187
链表的头结点一般为null，不算进链表长度
