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本篇文章介绍如何解决Java中的异常 Exception in thread "main" java.util.NoSuchElementException: No line found。

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

java.util.NoSuchElementException 是运行时未经检查的异常。 当我们使用 next()、nextElement()、迭代器、方法或枚举等方法时，JVM 会引发此异常。

当我们使用扫描仪通过 nextLine(); 等方法获取用户输入时，会出现错误 Exception in thread "main" java.util.NoSuchElementException: No line found 。 当我们尝试使用没有任何边界的方法时，就会发生错误。

让我们尝试一个演示此错误的示例。

package jiyik;

import java.util.Scanner;

public class Example {


    static boolean[][] Articles;
    public static void main(String[] args) {

        // This initiates all array values to be false
        Articles = new boolean[4][4];
        for (int i = 0; i < 4; i++) {
                for (int j = 0; j < 4; j++) {
                    Articles[i][j] = false;
                }

               // Welcome message
                System.out.println("-------------------------");
                System.out.println("Welcome to Jiyik.com.");
                System.out.println("-------------------------\n");

               // Starts program
               Programstart();
        }
    }

    public static void Programstart() {

      // to read users' input
       Scanner sc = new Scanner(System.in);

       //user input
        String Requested_Lanuguage;
        String Requested_Article;

        // Counters for articles array
        int Count_Language = 0;
        int Count_Artciles = 0;

        // User to select their choice of Programming Language
        System.out.print("Please type 1 for Java or 2 for Python: ");

        // Language preference
        Requested_Lanuguage = sc.nextLine();

        switch (Requested_Lanuguage) {
            case "1":
                // User selects Java
                System.out.println(">>> You have selected Java. \n");
                break;

            case "2":
                // User selects Python
                System.out.println(">>> You have selected Python. \n");
                break;

            default:
                // User has not selected a valid Programming Language
                System.out.println(">>> You have not selected a valid choice. Please try again. \n");
                Programstart();
                break;
        }

       // user to select their choice of article
       System.out.print("Please type 1 for Web and 2 for App: ");

       // Article preference
       Requested_Article = sc.nextLine();

       switch (Requested_Article) {
           case "1":
               // User selects Web Articles
               System.out.println(">>> You have selected Web Articles. \n");
               break;

           case "2":
               // User selects App Articles
               System.out.println(">>> You have selected App Articles. \n");
               break;

           default:
                // User has not selected a valid article
                System.out.println(">>> You have not selected a choice. Please try again. \n");
                Programstart();
                break;
            }

        // Closes Scanner
       sc.close();
    }
}

上面代码的输出是：

-------------------------
Welcome to Jiyik.com.
-------------------------

Please type 1 for Java or 2 for Python: 1
>>> You have selected Java.

Please type 1 for Web and 2 for App: 1
>>> You have selected Web Articles.

Exception in thread "main" -------------------------
Welcome to Jiyik.com.
-------------------------

Please type 1 for Java or 2 for Python: java.util.NoSuchElementException: No line found
    at java.base/java.util.Scanner.nextLine(Scanner.java:1651)
    at jiyik.Example.Programstart(Example.java:45)
    at jiyik.Example.main(Example.java:24)

发生错误是因为我们使用没有任何边界的方法 nextLine() 。 为了解决这个问题，我们需要替换代码 Requested_Article = sc.nextLine(); 到以下代码。

while(sc.hasNextLine()){
    Requested_Article = sc.nextLine();
    // Switch condition here
}

让我们尝试一下解决方案。

package jiyik;

import java.util.Scanner;

public class Example {

    static boolean[][] Articles;
    public static void main(String[] args) {

        // This initiates all array values to be false
        Articles = new boolean[4][4];
        for (int i = 0; i < 4; i++) {
                for (int j = 0; j < 4; j++) {
                    Articles[i][j] = false;
                }

               // Welcome message
                System.out.println("-------------------------");
                System.out.println("Welcome to Jiyik.com.");
                System.out.println("-------------------------\n");

               // Starts program
               Programstart();
        }
    }

    public static void Programstart() {

        // to read users' input
        Scanner sc = new Scanner(System.in);

        //user input
        String Requested_Lanuguage;
        String Requested_Article;

        // Counters for articles array
        int Count_Language = 0;
        int Count_Artciles = 0;

        // User to select their choice of Programming Language
        System.out.print("Please type 1 for Java or 2 for Python: ");

        // Language preference
        Requested_Lanuguage = sc.nextLine();

        switch (Requested_Lanuguage) {
            case "1":
                // User selects Java
                System.out.println(">>> You have selected Java. \n");
                break;

            case "2":
                // User selects Python
                System.out.println(">>> You have selected Python. \n");
                break;

            default:
                // User has not selected a valid Programming Language
                System.out.println(">>> You have not selected a valid choice. Please try again. \n");
                Programstart();
                break;
        }

       // user to select their choice of article
       System.out.print("Please type 1 for Web and 2 for App: ");

       // Article preference
       while(sc.hasNextLine()){
            Requested_Article = sc.nextLine();

       switch (Requested_Article) {
           case "1":
               // User selects Web Articles
               System.out.println(">>> You have selected Web Articles. \n");
               break;

           case "2":
               // User selects App Articles
               System.out.println(">>> You have selected App Articles. \n");
               break;

           default:
                // User has not selected a valid article
                System.out.println(">>> You have not selected a choice. Please try again. \n");
                Programstart();
                break;
            }
        }
        // Closes Scanner
       sc.close();
    }
}

上面的代码不会抛出 Exception in thread "main" java.util.NoSuchElementException: No line found now。 查看输出：

-------------------------
Welcome to Jiyik.com.
-------------------------

Please type 1 for Java or 2 for Python: 1
>>> You have selected Java.

Please type 1 for Web and 2 for App: 1
>>> You have selected Web Articles.

1
>>> You have selected Web Articles.


>>> You have not selected a choice. Please try again.

Please type 1 for Java or 2 for Python: