用java实现的双向链表增加删除修改操作

import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.util.Scanner;class Dnode{public int score=-1;public Dnode llink;public Dnode rlink;}class DoubleList{static Dnode pre,ptr,head,current;DoubleList(){ptr=new Dnode();ptr.llink=ptr;ptr.rlink=ptr;head=ptr;}public static void insert(Dnode ptr){Dnode first=head.rlink;ptr.rlink=head.rlink;ptr.llink=head;head.rlink=ptr;first.llink=ptr;} public static void delete(Dnode ptr){ptr.llink.rlink=ptr.rlink;ptr.rlink.llink=ptr.llink;ptr=null;}public static void modify(Dnode ptr,int m){ptr.score=m;}public static int length(){current=head.rlink;int count=0;while(current.rlink!=head){current=current.rlink;count++;}return count;}}public class Main {public static void main(String[] args) throws IOException {DoubleList doublist=new DoubleList();printDoublelist(doublist);//输出当前双向链表Scanner sc=new Scanner(new BufferedReader(new InputStreamReader(System.in)));while(true){System.out.println("1.插入 2.删除  3.修改");System.out.println("请输入要选择的操作序号：");int select=sc.nextInt();if(select==1){insertopp(doublist);}if(select==2){deleteopp(doublist);}if(select==3){modifyopp(doublist);}System.out.println();} }public static void insertopp(DoubleList doublist){//插入操作System.out.println("请输入待插入节点：");Scanner sc=new Scanner(new BufferedReader(new InputStreamReader(System.in)));int a=sc.nextInt();while(a!=0){  Dnode node=new Dnode();node.score=a;doublist.insert(node);a=sc.nextInt();}printDoublelist(doublist);}public static void deleteopp(DoubleList doublist){//删除操作System.out.println("请输入要删除节点序列号：");Scanner sc=new Scanner(new BufferedReader(new InputStreamReader(System.in)));int count=sc.nextInt();Dnode current=doublist.head;for(int i=1;i<=count;i++){  current=current.rlink;}doublist.delete(current);printDoublelist(doublist);}public static void modifyopp(DoubleList doublist){//修改操作System.out.println("请输入要修改节点序列号：");Scanner sc=new Scanner(new BufferedReader(new InputStreamReader(System.in)));int count=sc.nextInt();Dnode current=doublist.head;for(int i=1;i<=count;i++){  current=current.rlink;}System.out.println("请输入要修改的值：");int n=sc.nextInt();doublist.modify(current,n);printDoublelist(doublist);}public static void printDoublelist(DoubleList doublist){System.out.println("双向链表：");System.out.print("head"+"<->");   if(doublist.head.rlink!=doublist.head)   {Dnode current=doublist.head.rlink; int count=0;while(current.rlink!=doublist.head){System.out.print(current.score+"<->");current=current.rlink;}System.out.print(current.score);   }   System.out.println();   } }