为什么我收到错误“java.util.NoSuchElementException”？

Question

我的错误消息如下所示：

Exception in thread "main" java.util.NoSuchElementException: No line found
    at java.util.Scanner.nextLine(Scanner.java:1540)
    at GPA3.answer(GPA3.java:364)
    at GPA3.main(GPA3.java:355)

我有我的main方法，其余代码工作正常但是一旦我添加这段代码就会抛出错误。它不允许我在扫描仪中输入任何内容。

import java.util.Scanner;
public class GPA3 {

    public static void main(String[] args) 
    {
        System.out.println("Hello! Welcome to the GPA Calculator.");

        int Math;
        double mathGpa = 0;

        System.out.println("Math = ");
        Scanner input = new Scanner(System.in);
        Math= input.nextInt();

        if (Math >100){
            System.out.println("You have mistyped something");
        }
        if (Math >= 94){
            System.out.println("You have an A");
            mathGpa = 4.0;
            System.out.println(mathGpa);
        }
        if (Math < 94 && Math >=90){
            System.out.println("You have an A-");
            mathGpa = 3.7;
            System.out.println(mathGpa);
        }
        if (Math < 90 && Math >=87){
            System.out.println("You have a B+");
            mathGpa = 3.3;
            System.out.println(mathGpa);
        }
        if (Math < 87 && Math >=80){
            System.out.println("You have a B");
            mathGpa = 3.0;
            System.out.println(mathGpa);
        }
        if (Math < 80 && Math >=77){
            System.out.println("You have a B-");
            mathGpa = 2.7;
            System.out.println(mathGpa);
        }
        if (Math < 77 && Math >=73){
            System.out.println("You have a C+");
            mathGpa = 2.3;
            System.out.println(mathGpa);
        }
        if (Math < 73 && Math >=70){
            System.out.println("You have a C");
            mathGpa = 2.0;
            System.out.println(mathGpa);
        }
        if (Math < 70 && Math >=67){
            System.out.println("You have a C-");
            mathGpa = 1.7;
            System.out.println(mathGpa);
        }
        if (Math < 67 && Math >=67){
            System.out.println("You have a D+");
            mathGpa = 1.3;
            System.out.println(mathGpa);
        }
        if (Math < 67 && Math >=63){
            System.out.println("You have a D");
            mathGpa = 1.0;
            System.out.println(mathGpa);
        }
        if (Math < 63 && Math >=60){
            System.out.println("You have a D-");
            mathGpa = 0.7;
            System.out.println(mathGpa);
        }
        if (Math < 60){
            System.out.println("You have a F");
            mathGpa = 0.0;
            System.out.println(mathGpa);
        }//End of Math

        int English;
        double englishGpa = 0;
        System.out.println("English = ");
        English= input.nextInt();

        if (English >100){
            System.out.println("You have mistyped something");
        }
        if (English >= 94 && English <101){
            System.out.println("You have an A");
            englishGpa = 4.0;
            System.out.println(englishGpa);
        }
        if (English < 94 && English >=90){
            System.out.println("You have an A-");
            englishGpa = 3.7;
            System.out.println(englishGpa);
        }
        if (English < 90 && English >=87){
            System.out.println("You have a B+");
            englishGpa = 3.3;
            System.out.println(englishGpa);
        }
        if (English < 87 && English >=80){
            System.out.println("You have a B");
            englishGpa = 3.0;
            System.out.println(englishGpa);
        }
        if (English < 80 && English >=77){
            System.out.println("You have a B-");
            englishGpa = 2.7;
            System.out.println(englishGpa);
        }
        if (English < 77 && English >=73){
            System.out.println("You have a C+");
            englishGpa = 2.3;
            System.out.println(englishGpa);
        }
        if (English < 73 && English >=70){
            System.out.println("You have a C");
            englishGpa = 2.0;
            System.out.println(englishGpa);
        }
        if (English < 70 && English >=67){
            System.out.println("You have a C-");
            englishGpa = 1.7;
            System.out.println(englishGpa);
        }
        if (English < 67 && English >=67){
            System.out.println("You have a D+");
            englishGpa = 1.3;
            System.out.println(englishGpa);
        }
        if (English < 67 && English >=63){
            System.out.println("You have a D");
            englishGpa = 1.0;
            System.out.println(englishGpa);
        }
        if (English < 63 && English >=60){
            System.out.println("You have a D-");
            englishGpa = 0.7;
            System.out.println(englishGpa);
        }
        if (English < 60){
            System.out.println("You have a F");
            englishGpa = 0.0;
            System.out.println(englishGpa);
        }//End of English

        int Science;
        double SciGpa = 0;
        System.out.println("Science = ");
        Science= input.nextInt();

        if (Science >100){
            System.out.println("You have mistyped something");
        }
        if (Science >= 94 && Science <101){
            System.out.println("You have an A");
            SciGpa = 4.0;
            System.out.println(SciGpa);
        }
        if (Science < 94 && Science >=90){
            System.out.println("You have an A-");
            SciGpa = 3.7;
            System.out.println(SciGpa);
        }
        if (Science < 90 && Science >=87){
            System.out.println("You have a B+");
            SciGpa = 3.3;
            System.out.println(SciGpa);
        }
        if (Science < 87 && Science >=80){
            System.out.println("You have a B");
            SciGpa = 3.0;
            System.out.println(SciGpa);
        }
        if (Science < 80 && Science >=77){
            System.out.println("You have a B-");
            SciGpa = 2.7;
            System.out.println(SciGpa);
        }
        if (Science < 77 && Science >=73){
            System.out.println("You have a C+");
            SciGpa = 2.3;
            System.out.println(SciGpa);
        }
        if (Science < 73 && Science >=70){
            System.out.println("You have a C");
            SciGpa = 2.0;
            System.out.println(SciGpa);
        }
        if (Science < 70 && Science >=67){
            System.out.println("You have a C-");
            SciGpa = 1.7;
            System.out.println(SciGpa);
        }
        if (Science < 67 && Science >=67){
            System.out.println("You have a D+");
            SciGpa = 1.3;
            System.out.println(SciGpa);
        }
        if (Science < 67 && Science >=63){
            System.out.println("You have a D");
            SciGpa = 1.0;
            System.out.println(SciGpa);
        }
        if (Science < 63 && Science >=60){
            System.out.println("You have a D-");
            SciGpa = 0.7;
            System.out.println(SciGpa);
        }
        if (Science < 60){
            System.out.println("You have a F");
            SciGpa = 0.0;
            System.out.println(SciGpa);
        }//End of Science

        int Spanish;
        double SpanGpa = 0;
        System.out.println("Spanish = ");
        Spanish= input.nextInt();

        if (Spanish >100){
            System.out.println("You have mistyped something");
        }
        if (Spanish >= 94 && Spanish <101){
            System.out.println("You have an A");
            SpanGpa = 4.0;
            System.out.println(SpanGpa);
        }
        if (Spanish < 94 && Spanish >=90){
            System.out.println("You have an A-");
            SpanGpa = 3.7;
            System.out.println(SpanGpa);
        }
        if (Spanish < 90 && Spanish >=87){
            System.out.println("You have a B+");
            SpanGpa = 3.3;
            System.out.println(SpanGpa);
        }
        if (Spanish < 87 && Spanish >=80){
            System.out.println("You have a B");
            SpanGpa = 3.0;
            System.out.println(SpanGpa);
        }
        if (Spanish < 80 && Spanish >=77){
            System.out.println("You have a B-");
            SpanGpa = 2.7;
            System.out.println(SpanGpa);
        }
        if (Spanish < 77 && Spanish >=73){
            System.out.println("You have a C+");
            SpanGpa = 2.3;
            System.out.println(SpanGpa);
        }
        if (Spanish < 73 && Spanish >=70){
            System.out.println("You have a C");
            SpanGpa = 2.0;
            System.out.println(SpanGpa);
        }
        if (Spanish < 70 && Spanish >=67){
            System.out.println("You have a C-");
            SpanGpa = 1.7;
            System.out.println(SpanGpa);
        }
        if (Spanish < 67 && Spanish >=67){
            System.out.println("You have a D+");
            SpanGpa = 1.3;
            System.out.println(SpanGpa);
        }
        if (Spanish < 67 && Spanish >=63){
            System.out.println("You have a D");
            SpanGpa = 1.0;
            System.out.println(SpanGpa);
        }
        if (Spanish < 63 && Spanish >=60){
            System.out.println("You have a D-");
            SpanGpa = 0.7;
            System.out.println(SpanGpa);
        }
        if (Spanish < 60){
            System.out.println("You have a F");
            SpanGpa = 0.0;
            System.out.println(SpanGpa);
        }//End of Spanish

        int Religion;
        double RGpa = 0;
        System.out.println("Religion = ");
        Religion= input.nextInt();
        input.close();

        if (Religion >100){
            System.out.println("You have mistyped something");
        }
        if (Religion >= 94 && Religion < 101){
            System.out.println("You have an A");
            RGpa = 4.0;
            System.out.println(RGpa);
        }
        if (Religion < 94 && Religion >=90){
            System.out.println("You have an A-");
            RGpa = 3.7;
            System.out.println(RGpa);
        }
        if (Religion < 90 && Religion >=87){
            System.out.println("You have a B+");
            RGpa = 3.3;
            System.out.println(RGpa);
        }
        if (Religion < 87 && Religion >=80){
            System.out.println("You have a B");
            RGpa = 3.0;
            System.out.println(RGpa);
        }
        if (Religion < 80 && Religion >=77){
            System.out.println("You have a B-");
            RGpa = 2.7;
            System.out.println(RGpa);
        }
        if (Religion < 77 && Religion >=73){
            System.out.println("You have a C+");
            RGpa = 2.3;
            System.out.println(RGpa);
        }
        if (Religion < 73 && Religion >=70){
            System.out.println("You have a C");
            RGpa = 2.0;
            System.out.println(RGpa);
        }
        if (Religion < 70 && Religion >=67){
            System.out.println("You have a C-");
            RGpa = 1.7;
            System.out.println(RGpa);
        }
        if (Religion < 67 && Religion >=67){
            System.out.println("You have a D+");
            RGpa = 1.3;
            System.out.println(RGpa);
        }
        if (Religion < 67 && Religion >=63){
            System.out.println("You have a D");
            RGpa = 1.0;
            System.out.println(RGpa);
        }
        if (Religion < 63 && Religion >=60){
            System.out.println("You have a D-");
            RGpa = 0.7;
            System.out.println(RGpa);
        }
        if (Religion < 60){
            System.out.println("You have a F");
            RGpa = 0.0;
            System.out.println(RGpa);
        }//End of Religion 
        answer();
    }//End of Main

    public static double answer()
        {//Begin answer
        double sClass=0;
        System.out.println("Do you have gym this semester?");
        Scanner input = new Scanner(System.in);
        String yes = "yes";
        String answer = input.nextLine();

        if (answer.equals(yes)){

        }
        input.close();
        return sClass;
    }//End answer

}

Answer 1

问题是您尝试在同一个流上同时打开两个不同的Scanner对象 - System.in - 两个都同时打开，这导致第二个扫描程序出现问题试图从流中读取。

您可以做的是让answer()函数接受Scanner对象作为参数，然后使用它而不是在同一个流上创建一个新对象。

示例 -

    .... // Lots of logic till here
    }//End of Religion 
    answer(input);
}//End of Main

public static double answer(Scanner input)
    {//Begin answer
    double sClass=0;
    System.out.println("Do you have gym this semester?");
    String yes = "yes";
    String answer = input.nextLine();

    if (answer.equals(yes)){

    }
    input.close();
    return sClass;
}//End answer

您还需要删除input.close();，因为它会关闭System.in的基础流。