双链表的实现原理与单链表的基本一致，不同之处只是在于双链表的结点增加了一个前驱指针域，用来指向它的前驱结点，可以实现链表的双向遍历，在插入和删除结点是也更方便
可以参考单链表来看https://blog.csdn.net/qq_34517044/article/details/102817627
package Datastruct; class DoubleLinkList<Item>{ private class Node{ Item item; Node prenext; Node latnext; } private Node first; private Node last; private int N; public boolean isEmpty() { return first==null; } public int size() { return N; } public void put(Item item) { Node oldlast=last; last=new Node(); last.item=item; if(isEmpty()) first=last; else { oldlast.latnext=last; last.prenext=oldlast; } N++; } public void search(int i) { if(isEmpty()) { System.out.println("List is Empty,Search fail"); return; } if(i<1||i>N) { System.out.println("Search Exceed"); return; } else { Node x=first; int count=0; for(;x!=null;x=x.latnext) { count++; if(i==count) break; } System.out.println(x.item); } } public void change(int i,Item item) { if(isEmpty()) { System.out.println("List is Empty,Change fail"); return; } if(i<1||i>N) { System.out.println("Change Exceed"); return; } else { Node x=first; int count=0; for(;x!=null;x=x.latnext) { count++; if(count==i) break; } x.item=item; } } public void insert(Item item,int i) { if(i==1) { Node oldfirst=first; first=new Node(); first.item=item; first.latnext=oldfirst; oldfirst.prenext=first; } else { Node x=first; int count=0; for(;x!=null;x=x.latnext) { count++; if(i==count) break; } Node n=new Node(); n.item=item; n.prenext=x.prenext; n.latnext=x; x.prenext.latnext=n; x.prenext=n; } N++; } public void delete(int i) { if(isEmpty()) { System.out.println("List is Empty,delete fail"); return; } if(i==1) { first=first.latnext; first.prenext=null; } else if(i==N) { Node x=first; int count=0; for(;x!=null;x=x.latnext) { count++; if(count==i) break; } x.prenext.latnext=null; last=x.prenext; } else { Node x=first; int count=0; for(;x!=null;x=x.latnext) { count++; if(i==count) break; } x.prenext.latnext=x.latnext; x.latnext.prenext=x.prenext; } N--; } public void show() { if(isEmpty()) { System.out.println("链表为空"); return; } else { Node x=first; for(;x!=null;x=x.latnext) { System.out.print(x.item+" "); } System.out.println(); } } } public class DoubleLinkListTest { public static void main(String[] args) { DoubleLinkList<Integer> l=new DoubleLinkList<Integer>(); l.put(1); l.put(3); l.put(2); l.put(5); l.change(3,7); l.show(); System.out.println("链表大小:"+l.size()); l.insert(8,2); l.show(); l.delete(2); l.show(); } }因为用的是泛型，测试时可以任意指定基本对象类型
测试结果是对的，可以自行测试
