链表图书管理系统

import java.util.Scanner;
abstract class Manager{
	abstract void add(Book book);
	abstract void del(String ISBN);
	abstract void check(String ISBN);
	abstract void amen(String ISBN);
}
class Book{
	String ISBN;
	String name;
	String author;
	Book next;	
	public Book(){		
	} 
	public Book(Book book,Book next){
		this.ISBN=book.ISBN;
		this.name=book.name;
		this.author=book.author;
		this.next=next;
	}
	public Book(String iSBN, String name, String author, Book next) {
		super();
		ISBN = iSBN;
		this.name = name;
		this.author = author;
		this.next = next;
	}
}
public class LinkedBookManger extends Manager{
	Book list;
	Book last;
	int size=0;
	public LinkedBookManger(){
		list=new Book();
		list.next=list;
		last=list;
	}
	void add(Book book) {
		Book s=new Book(book,last.next);
		last.next=s;
		last=s;
		size++;
	}
	void del(String ISBN) {
		Book p=list.next;
		Book var = list;
		while(p != list) {
			if(p.ISBN.equals(ISBN)) {
				var.next = p.next;
				System.out.println("已删除");
				size--;
				return;
			}			
			var = p;
			p = p.next;
		}
		System.out.println("");
	}
	void check(String ISBN) {	
		Book p=list;
		while(p.next!=list) {
			p=p.next;
			if(p.ISBN.equals(ISBN)) {
				System.out.println("书的ISBN:"+p.ISBN+"，书名："+p.name+"，作者："+p.author);
				return;
			}	
		}
		System.out.println("没有找到:"+ISBN);
	}
	void amen(String ISBN){
		Scanner sc=new Scanner(System.in);
		Book p=list;
		while(p.next!=list) {
			p=p.next;
			if(p.ISBN.equals(ISBN)) {
				System.out.println("请输入您要修改的信息：");
				String book=sc.next();
				if(book.equals("ISBN")) {
					System.out.println("请输入修改后的ISBN：");
					book=sc.next();
					p.ISBN=book;
					System.out.println("修改成功");
				}
				else if(book.equals("书名")) {
					System.out.println("请输入修改后的书名：");
					book=sc.next();
					p.name=book;
					System.out.println("修改成功");
				}
				else if(book.equals("作者")) {
					System.out.println("请输入修改后的作者：");
					book=sc.next();
					p.author=book;
					System.out.println("修改成功");
				}
				else {
					System.out.println("没有此类信息！");
				}
			}	
		}
	}
}

import java.util.Scanner;
public class Test {
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		LinkedBookManger link=new LinkedBookManger();
		System.out.print("增加请按1；删除请按2；查找请按3；修改请按4；程序结束请按5：");
		int a=sc.nextInt();
		while(a>=1||a<=4) {										
			if(a==1) {
				System.out.print("请输入您要添加的书本数量：");
				int b=sc.nextInt();
				Book[] books=new Book[b];
				for(int i=0;i 
测试：