java - 线程中的异常 "main"java.util.NoSuchElementException : No line found at java. util.Scanne

Question

这个问题已经有答案了:

java util scanner throwforunknown source error (cant type input) (1 个回答)

已关闭 8 年前。

为学校期末项目制作此程序。当我尝试运行时出现错误，并且不确定需要做什么来修复它。错误说:

Exception in thread "main" java.util.NoSuchElementException: No line found

at java.util.Scanner.nextLine(Scanner.java:1585)

at BusinessCardMaker.getName(BusinessCardMaker.java:41)

at BusinessCardMaker.instructions(BusinessCardMaker.java:28)

at BusinessCardMaker.main(BusinessCardMaker.java:131)

我做错了什么。我可以改变什么来使程序变得更好？我的代码有什么问题导致了这些错误？

提前感谢大家!

import java.util.Scanner;
import java.io.*;
import java.util.Random;
public class BusinessCardMaker{
    private static String wholeName;
    private static String firstLineAddress;
    private static String secondLineAddress;
    private static String company;
    private static String location;
    private static String jobTitle;
    private static int officePhoneNum;
    private static String extNum;
    private static int input;
    private static String email;
    private static int cellNum;
    private static int cardNumber;
    public static void instructions()  throws IOException{
        System.out.println("Welcome to your very own Business Card Maker");
        System.out.println("\nTo access the program please type 1");
        Scanner keyboard = new Scanner(System.in);
        int startProgram = keyboard.nextInt();
        keyboard.close();
        if(startProgram == 1)
        {
            getName();
            getAddress();
            getDepartment();
            getPhoneNums();
            getEmail();
            generateCardNum();
            cardMaker();
        }
    }
    public static void getName()
    {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Please input your whole name in this format (First M. Last)");
        wholeName = keyboard.nextLine();
        keyboard.close();
    }
    public static void getAddress(){
        Scanner keyboard = new Scanner(System.in);
        System.out.println("What is the first line of your address?");
        firstLineAddress = keyboard.nextLine();
        System.out.println("What is the second line of your address?");
        secondLineAddress = keyboard.nextLine();
        keyboard.close();
    }
    public static void getDepartment(){
        Scanner keyboard = new Scanner(System.in);
        System.out.println("What company do you work for?");
        company = keyboard.nextLine();
        System.out.println("What particular location of company do you work for?");
        location = keyboard.nextLine();
        System.out.println("What is your primary position?");
        jobTitle = keyboard.nextLine();
        keyboard.close();
    }
    public static void getPhoneNums()
    {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("What is your cell phone number?");
        cellNum = keyboard.nextInt();
        System.out.println("What is your office phone number?");
        officePhoneNum = keyboard.nextInt();
        System.out.println("Do you have and office extention? If yes enter 1, if no enter 0");
        input = keyboard.nextInt();
        if (input == 1) {
            Scanner keyboardExt = new Scanner(System.in);
            System.out.println("What is your extention number?");
            extNum = keyboardExt.nextLine();
            keyboardExt.close();
        } else {
            extNum = "N/A";
        }
        keyboard.close();
    }
    public static void getEmail(){
        Scanner keyboard = new Scanner(System.in);
        System.out.println("What is your Email Address?");
        email = keyboard.nextLine();
        keyboard.close();
    }
    public static void generateCardNum(){
        System.out.println("We automatically generated a random business card number");
        Random random = new Random();
        cardNumber = random.nextInt(1000) + 1;
    }
    public static void save() throws IOException    {
        String businessCard = "Business_Card.txt";
        File myFile = new File (businessCard);
        PrintWriter writer = new PrintWriter(myFile);
        System.out.println("Your card has been saved to " + businessCard);
        writer.println("\n\n            Your Business Card");
        writer.println("\n*****************************************************************************");
        writer.println("Card Number:" + cardNumber);
        writer.println("\n"+company);
        writer.println("\n\n\n\n\n                               "+wholeName);
        writer.println("                               "+jobTitle);
        writer.println("\n\n\n\n\n");
        writer.println(location+"                                    "+"Office:"+officePhoneNum+"Ext:"+extNum);
        writer.println(firstLineAddress+"                                    "+"Cell:"+cellNum);
        writer.println(secondLineAddress+"                                    "+"Email:"+email);   
        writer.close();
        }
    public static void checkForFile() throws IOException{
    String businessCard = "Business_Card.txt";
    File myFile = new File (businessCard);
    if(!myFile.exists()){
        myFile.createNewFile();
    }
    }
    public static void cardMaker() throws IOException   {
        System.out.println("\n\n            Your Business Card");
        System.out.println("\n*****************************************************************************");
        System.out.println("Card Number:" + cardNumber);
        System.out.println("\n"+company);
        System.out.println("\n\n\n\n\n                               "+wholeName);
        System.out.println("                               "+jobTitle);
        System.out.println("\n\n\n\n\n");
        System.out.println(location+"                                    "+"Office:"+officePhoneNum+"Ext:"+extNum);
        System.out.println(firstLineAddress+"                                    "+"Cell:"+cellNum);
        System.out.println(secondLineAddress+"                                    "+"Email:"+email);          
        checkForFile();
        save();
    }
    public static void main (String[]args)  throws IOException{
        instructions();
    }
}

Answer 1

keyboard.hasNextLine() 必须在调用 keyboard.nextLine() 之前返回 true

根据您真正想要实现的目标，您可能希望像这样使用它:

if(keyboard.hasNextLine()) {
  String line = keyboard.nextLine();
}

.hasNextLine() 被动地阻塞等待行出现(新行字符出现)，因此下一个解决方案是将调用包围起来

keyboard.nextLine()

使用 try/catch。