Java双向链表实现

本文实现了java双链表的基本的增删改查功能。有不足之处，望不吝赐教。

 

双链表 注意要点

1  双链表实现时第一个节点的前驱为空，最后一个节点的后驱为空。

2  删除尾节点 不需要从头开始遍历 从结尾开始遍历 复杂度变为O(1)

3  删除节点的本质是取消其他节点对该节点的引用

4  无论是删除指定位置的节点还是删除指定数据的节点 本质上是删除current指向的节点

5  插入节点本质上是在current 以及 current之前的prior  之间插入节点

6 searchItem 方法的while内部的判断条件为 while(current.data!=data&&current.next!=null) 为的是保证下面的current.data不会抛出NullPoiterException 。搜索到最后一个位置时，current为最后节点，判断此前的节点的info是否等于data，等于data，则返回，不等，则不存在该元素。

7 这里pos与current同步，pos从1开始，删除节点就是删除current。 

 

package com.marthevin.linkedlist;public class DoublyListTest {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubDoublyList doublyListTest = new DoublyList();doublyListTest.addFirstNode(32);doublyListTest.addFirstNode(23);doublyListTest.addFirstNode(56);doublyListTest.addFirstNode(212);doublyListTest.addFirstNode(6565);doublyListTest.addFirstNode(986);doublyListTest.addFirstNode(345);doublyListTest.addLastNode(3434);//System.out.println("链表原长度："+doublyListTest.lenth());//doublyListTest.insertNodeByPos(2, 555);//doublyListTest.addFirstNode(555);//doublyListTest.deleteNodeByData(345);//doublyListTest.deleteNodeByPos(5);//System.out.println("链表现有长度："+doublyListTest.lenth());doublyListTest.deleteNodeByData(3434);doublyListTest.displayForward();}}class DNode{DNode next,back;int data;public DNode(int data){this.data = data;this.next = null;this.back = null;}}class DoublyList{DNode first,last;int count = 0;int pos = 1;public DoublyList(){this.first = null;this.last = null;this.count = 0;}//确定链表是否为空public boolean isEmpty(){return this.count==0;}//确定链表的长度public int lenth(){return this.count;}//正向输出链表public void displayForward(){DNode current = first;if(first==null){System.out.println("空链表！");}else{while(current!=null){System.out.print(" "+current.data);current = current.next;}}}//反向输出链表public void displayBackward(){DNode current = last;if(first==null){System.out.println("空链表！");}else{while(current!=null){System.out.print(" "+current.data);current = current.back;}}}//搜索链表的元素 返回pos  下标从1开始 OKpublic int searchItem(int data){if(first == null){System.out.println("空链表！");return 0;}else{DNode current = first;int dataPos = 0;while(current.data!=data&¤t.next!=null){current = current.next;this.pos++;}if(current.data == data){dataPos = this.pos;this.pos = 1;return dataPos;}else{System.out.println("不存在该元素！");this.pos = 1;return 0;}}}//向链表中插入元素 下标从1之后开始public boolean insertNodeByPos(int pos, int data){boolean flag = false;DNode newnode = new  DNode(data);DNode current=null,prior=null;if(pos<=1||pos>count+1){System.out.println("Pos error!");return flag;}if(pos==count+1){ //在末尾插入节点newnode.back = last;last.next = newnode;last = newnode;count++;flag = true;}else //在其他位置插入节点{current = first;prior = first;while(this.pos<pos){prior = current;current = current.next;this.pos++;}prior.next = newnode;newnode.back = prior;newnode.next = current;current.back = newnode;this.count++;this.pos = 1;flag = true;}return flag;}//在链表前插入元素public void addFirstNode(int data){DNode newnode = new DNode(data);if(first == null){first = newnode;last = newnode;count++;}else{newnode.next = first;first.back = newnode;first = newnode;count++;}}//在链表后插入元素public void addLastNode(int data){DNode newnode = new DNode(data);if(first==null){first = newnode;last = newnode;count++;}else{newnode.back = last;last.next = newnode;last = newnode;count++;}}//删除指定位置的元素public boolean deleteNodeByPos(int pos){boolean flag = false;if(pos<1||pos>count){System.out.println("pos error!");return flag;}if(pos==1){ //删除首节点if(count==1)  //只有一个节点 删除之{first = null;last = null;count--;flag = true;}else{  //大于一个节点 删除首节点DNode second = first.next;first = first.next;second.back = null;count--;flag = true;}}else if(pos == count){ //删除尾节点if(count==1)  //只有一个节点 删除之{first = null;last = null;count--;flag = true;}else{  //大于一个节点 删除尾节点DNode lbnl = last.back; //倒数第二个节点last = lbnl;lbnl.next = null;count--;flag = true;}}else{  //删除除首尾节点的其他节点 从头开始搜索或者从最后开始搜索DNode current = first,prior = first;while(this.pos<pos){prior = current;current = current.next;this.pos++;}DNode afterCurrent = current.next;prior.next = afterCurrent;afterCurrent.back = prior;count--;this.pos = 1;flag = true;}return flag;}//给定元素 删除指定节点 删除第一个出现的节点public boolean deleteNodeByData(int data){boolean flag = false;if(first==null){System.out.println("空链表，无法删除！");return flag;}else{DNode current = first,prior = first;while(current.data!=data&¤t.next!=null){prior = current;current = current.next;this.pos++;}if(this.pos==1) //首节点{DNode second = first.next;first = first.next;second.back = null;count--;flag = true;}else if(this.pos == count)//尾节点{if(current.data==data){DNode lbnl = last.back; //倒数第二个节点last = lbnl;lbnl.next = null;count--;flag = true;}else{ //未找到System.out.println("未找到该元素！");flag = false;}}else{DNode afterCurrent = current.next;prior.next = afterCurrent;afterCurrent.back = prior;count--;this.pos = 1;flag = true;}}return flag;}}