调用方法时 NoSuchElementException 不起作用

Question

import java.util.*;

public class Main {
  static void factorFinder() {
    Scanner sc = new Scanner(System.in);
    boolean valid = false;
    int number = 0;
    
    
    while(! valid ){
      System.out.println("Enter the number you want to find the factor of(Numbers only)");
      try {
        number = sc.nextInt(); 
        valid = true;
      } catch (InputMismatchException e) {
            System.out.println("Not a number.");
            sc.next();
    }
      }
    sc.close();
    
    System.out.print("Factors of " + number + " are: ");
    for (int i = 1; i <= number; ++i) {

      // if number is divided by i
      // i is the factor
      if (number % i == 0) {
        System.out.print(i + " ");
      }
    }
  }
  public static void main(String[] args) {
    Scanner choiceScanner = new Scanner(System.in);
    System.out.println("Do you want to use the factor finder? (y/n)");
    String answer = choiceScanner.nextLine();
    choiceScanner.close();
    if(answer.equals("y")){
      factorFinder();
    }else{
      System.exit(0);
    }
    }
}

这是终端输出（通过replit运行）

 sh -c javac -classpath .:target/dependency/* -d . $(find . -type f -name '*.java')
 java -classpath .:target/dependency/* Main
Do you want to use the factor finder? (y/n)
y
Enter the number you want to find the factor of(Numbers only)
Exception in thread "main" java.util.NoSuchElementException
    at java.base/java.util.Scanner.throwFor(Scanner.java:937)
    at java.base/java.util.Scanner.next(Scanner.java:1594)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
    at Main.factorFinder(Main.java:13)
    at Main.main(Main.java:38)
exit status 1
 

我正在制作一个计算器，可以找到给定数字的因数。 计算器部分已完成并且正在工作。 但是，它要求使用计算器的部分不起作用。 它给出了 NoSuchElementException 错误。 有人可以帮助我吗？

Answer 1

关闭Scanner后，您将无法读取另一个 Scanner。

因此，您有两种可能的解决方案（如我所见）：

1（推荐）。 仅使用一台Scanner 。 您可以使其成为类成员或将其作为参数传递给方法。

import java.util.*;

public class Main {
  static Scanner sc = new Scanner(System.in);
  static void factorFinder() {
    boolean valid = false;
    int number = 0;
    
    
    while(! valid ){
      System.out.println("Enter the number you want to find the factor of(Numbers only)");
      try {
        number = sc.nextInt(); 
        valid = true;
      } catch (InputMismatchException e) {
            System.out.println("Not a number.");
            sc.next();
    }
      }
    System.out.print("Factors of " + number + " are: ");
    for (int i = 1; i <= number; ++i) {

      // if number is divided by i
      // i is the factor
      if (number % i == 0) {
        System.out.print(i + " ");
      }
    }
  }
  public static void main(String[] args) {
    System.out.println("Do you want to use the factor finder? (y/n)");
    String answer = choiceScanner.nextLine();
    if(answer.equals("y")){
      factorFinder();
    }else{
      sc.close();
      System.exit(0);
    }
    sc.close();
    }
}

2. 只有在调用factorFinder()方法后才关闭choiceScanner 。

Answer 2

public class Main2 {
    static Scanner sc = new Scanner(System.in);
    static void factorFinder() {
        boolean valid = false;
        int number = 0;


        while(! valid ){
            System.out.println("Enter the number you want to find the factor of(Numbers only)");
            try {
                number = sc.nextInt();
                valid = true;
            } catch (InputMismatchException e) {
                System.out.println("Not a number.");
                sc.next();
            }
        }
        System.out.print("Factors of " + number + " are: ");
        for (int i = 1; i <= number; ++i) {

            // if number is divided by i
            // i is the factor
            if (number % i == 0) {
                System.out.print(i + " ");
            }
        }
    }
    public static void main(String[] args) {
        Scanner choiceScanner = new Scanner(System.in);
        System.out.println("Do you want to use the factor finder? (y/n)");
        String answer = choiceScanner.nextLine();
        if(answer.equals("y")){
            factorFinder();
        }else{
            sc.close();
            System.exit(0);
        }
        sc.close();
    }
}