为什么nextLine（）返回一个空字符串？ [英] Why is nextLine() returning an empty string?

问题描述

这可能是最简单的事情之一，但我没看到我做错了什么。

This is probably one of the easiest things but I'm not seeing what I'm doing wrong.

我的输入包含一个带数字的第一行（要读取的行数），一堆包含数据的行和一行只包含\ n的行。我应该处理这个输入，在最后一行之后，做一些工作。

My input consist of one first line with a number (the number of lines to read), a bunch of lines with data and a final line only with \n. I should process this input and after the last line, do some work.

我有这个输入：

5
test1
test2
test3
test4
test5
      /*this is a \n*/

为了阅读输入，我有这个代码。

And for reading the input I have this code.

int numberRegisters;
String line;

Scanner readInput = new Scanner(System.in);

numberRegisters = readInput.nextInt();

while (!(line = readInput.nextLine()).isEmpty()) {
    System.out.println(line + "<");
}

我的问题是为什么我不打印任何东西？程序读取第一行，然后什么都不做。

My question is why I'm not printing anything? Program reads the first line and then does nothing.

推荐答案

nextInt 不不要读取以下换行符，所以第一个 nextLine （返回当前行的其余部分）将始终返回一个空字符串。

nextInt doesn't read the following new-line character, so the first nextLine (which returns the rest of the current line) will always return an empty string.

这应该有效：

numberRegisters = readInput.nextInt();
readInput.nextLine();
while (!(line = readInput.nextLine()).isEmpty()) {
    System.out.println(line + "<");
}

但我的建议是不要混合 nextLine with nextInt / nextDouble / next /等因为任何试图维护代码（包括你自己）的人都可能没有意识到或忘记了上述代码，所以可能会对上述代码感到有些困惑。

But my advice is not to mix nextLine with nextInt / nextDouble / next / etc. because anyone trying to maintain the code (yourself included) may not be aware of, or have forgotten, the above, so may be somewhat confused by the above code.

所以我建议：

numberRegisters = Integer.parseInt(readInput.nextLine());

while (!(line = readInput.nextLine()).isEmpty()) {
    System.out.println(line + "<");
}

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