如何停止使用Scanner从stdin读取多行? [英] How to stop reading multiple lines from stdin using Scanner?

问题描述

我正在处理JAVA分配，应该处理多行输入.指示信息为从标准输入中读取输入".

I'm working on an JAVA assignment should process multiple lines of input. The instructions read "Input is read from stdin."

给出了示例输入示例:

one 1
two 2
three 3

我不明白上面的示例输入从stdin读取"是什么意思.

I don't understand what the above sample input "read from stdin" means.

这是我编写的一个测试程序，可以消除我的困惑:

Here's a test program I wrote that isolates my confusion:

import java.io.*;
import java.util.Scanner;

class Test
{
public static void main(String[] args)
{   
    Scanner stdin = new Scanner(System.in);
    while(stdin.hasNextLine())
    {
        String line = stdin.nextLine();
        String[] tokens = line.split(" ");
        System.out.println(Integer.parseInt(tokens[1]));
    }
}

当我在控制台中运行该程序时，它会等待我的输入，并且每当我输入一行时，它就会像预期的那样回显它.因此，我认为也许可以通过以这种方式输入3条线中的每条线来实现上面的示例输入.但是，似乎没有办法结束该过程.输入3行后，如何终止输入?我尝试只按两次Enter键，但这似乎读为仅包含换行符的行，这会导致错误，因为该行不符合预期的2个标记格式.

When I run this program in the console, it waits for my input and each time I input a line it echos it back as I would expect. So I thought perhaps the sample input above would be achieved by entering each of the 3 lines in this fashion. However, there seems to be no way to end the process. After I enter the 3 lines, how do I terminate the input? I tried just pressing enter twice, but that seems to read as a line consisting of only the newline character, which causes an error because the line doesn't fit the 2 token format it expects.

这是控制台交互的样子:

Here's what the console interaction looks like:

javac Test.java
java Test
one 1
1
two 2
2
three 3
3

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
    at Test.main(Test.java:13)

如果能帮助我指出我的理解方面的空白，我将不胜感激.

I'd appreciate any help in pointing out the gap in my understanding.

推荐答案

您可以尝试要求输入空值

import java.util.Scanner;

public class Test
{
    public static void main(String[] args)
    {   
        String line;
        Scanner stdin = new Scanner(System.in);
        while(stdin.hasNextLine() && !( line = stdin.nextLine() ).equals( "" ))
        {
            String[] tokens = line.split(" ");
            System.out.println(Integer.parseInt(tokens[1]));
        }
        stdin.close();
    }
}

• 您的代码即将完成.您要做的就是退出while循环.在此代码示例中，我向其添加了一个条件，该条件首先将读取的输入值设置为line，然后检查返回的String是否为空.如果是，则while循环的第二个条件返回false并使其停止.
• 仅在不输入两个值(由空格分隔)的最小值时，才会获得数组索引超出范围的异常.如果您不尝试获取第二个值，则> token [1]<通过静态索引可以避免此错误.
• 使用阅读器时，请记住在使用阅读器后将其关闭.
• 最后但并非最不重要的-您是否尝试过使用通常的Ctrl + C热键终止控制台中的进程?
• Your code is almost completed. All that you have to do is to exit the while loop. In this code sample I added a condition to it that first sets the read input value to line and secondly checks the returned String if it is empty; if so the second condition of the while loop returns false and let it stop.
• The array index out of bounds exception you will only get when you're not entering a minimum of two values, delimitted by whitespace. If you wouldn't try to get the second value >token[1]< by a static index you could avoid this error.
• When you're using readers, keep in mind to close after using them.
• Last but not least - have you tried the usual Ctrl+C hotkey to terminate processes in consoles?

祝你好运！

这篇关于如何停止使用Scanner从stdin读取多行?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！