java - 调用函数给出 "NoSuchElementException"

Question

我正在编写一个简单的 Java 程序来解释循环。我希望每个演示都在一个单独的函数中。现在，每个函数都可以正常工作，但只有在另一个函数未被调用时才能正常工作。如果我同时调用两者，我会在运行时收到以下错误:

Please input a positive integer as the end value: 5
The summation is: 9
How many rows do you want your triangle to be?: Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at loops.exercise2(loops.java:48)
at loops.main(loops.java:11)

代码:

import java.util.Scanner;

public class loops
{

public static void main( String args[] )
{
    exercise1();
    System.out.println();
    exercise2();
}

public static void exercise1()
{

    int limit;
    int i;
    int sum;

    Scanner keyboard = new Scanner(System.in);


    System.out.print ("Please input a positive integer as the end value: ");

    limit = keyboard.nextInt();

    i=1;
    sum = 0;

    while (i <= limit)
    {
        sum = sum + i;
        i = i + 2;          
    }

    System.out.print("The summation is: " + sum);

    keyboard.close();
}

public static void exercise2()
{
    int numRows, i, j;
    Scanner keyboard = new Scanner(System.in);

    System.out.print("How many rows do you want your triangle to be?: ");
    numRows = keyboard.nextInt();

    for(i=0; i<numRows; i++)
    {
        for(j=0; j<=i; j++)
        {
            System.out.print("*");              
        }
        System.out.println();
    }

    keyboard.close();
}

Answer 1

发生这种情况是因为当您关闭 Scanner 时，它也会关闭输入流，在本例中为 System.in。当您尝试在 execise2 方法中实例化 Scanner 时，输入流已关闭。

查看此 SO 帖子...

https://stackoverflow.com/a/13042296/1246574