就是不知道input.naxtLine();什么意思

package com.sun.one;
import java.util.*;
public class BookSystem {
    static Scanner input=new Scanner(System.in);
    static String[] bookName={"小王子","追风筝的人","野火集"};
    
    public static void main(String[] args) {
        welcome();
    }
    
        public static void welcome(){
        System.out.println("输入命令：1-按照名称查找图书    2-按照序号查找图书");
        try{
        switch(input.nextInt()){
        case 1:
            searchName();
            break;
        case 2:
            searchNum();
            break;
        default:
            System.out.println("命令输入有误，请根据提示输入数字命令");    
            input.nextLine();
             welcome();
        }    
    }catch(Exception e){
            System.out.println("命令输入有误，请根据提示输入数字命令");
            input.nextLine();
             welcome();
          }
    }
    public static void searchName(){
        System.out.print("请输入您要查找的书名：");
        String name=input.next();
        @SuppressWarnings("unused")
        Boolean key=false;
        for(int i=0;i<bookName.length;i++){
            if(name.equals(bookName[i]))
                key=true;
            }
        if(key=true){
                System.out.println("book:"+name);
        }else{
                System.out.println("图书不存在！");
                input.nextLine();
                welcome();
            }
            
        }
     
    public static void searchNum(){
        try{System.out.println("请输入您要查找的书序号：");
        int num=input.nextInt();
        System.out.println(bookName[num-1]);
        
        }catch(InputMismatchException e){
            System.out.println("命令输入有误，请根据提示输入数字命令");
            input.nextLine();
            searchNum();
        }catch(Exception e){
            System.out.println("图书不存在！");
            input.nextLine();
            welcome();
        }
        
        
    }

}