在 Java 中从 System.in 读取的最快方法是什么? [英] What's the fastest way to read from System.in in Java?

问题描述

我正在使用 Scanner(System.in) 从标准中读取由空格或换行符分隔的一堆整数.

I am reading bunch of integers separated by space or newlines from the standard in using Scanner(System.in).

在 Java 中是否有更快的方法?

Is there any faster way of doing this in Java?

推荐答案

在 Java 中是否有更快的方法?

是的.扫描仪相当慢(至少根据我的经验).

Yes. Scanner is fairly slow (at least according to my experience).

如果您不需要验证输入，我建议您将流包装在 BufferedInputStream 中并使用类似 String.split/Integer.parseInt 的内容.

If you don't need to validate the input, I suggest you just wrap the stream in a BufferedInputStream and use something like String.split / Integer.parseInt.

一个小的比较:

使用此代码读取 17 兆字节(4233600 个数字)

Reading 17 megabytes (4233600 numbers) using this code

Scanner scanner = new Scanner(System.in);
while (scanner.hasNext())
    sum += scanner.nextInt();

在我的机器上3.3 秒.而这个片段

took on my machine 3.3 seconds. while this snippet

BufferedReader bi = new BufferedReader(new InputStreamReader(System.in));
String line;
while ((line = bi.readLine()) != null)
    for (String numStr: line.split("\s"))
        sum += Integer.parseInt(numStr);

用了 0.7 秒.

通过进一步弄乱代码(使用 String.indexOf/String.substring 遍历 line)，您可以将其缩减为大约0.1 秒很容易，但我想我已经回答了你的问题，我不想把它变成一些代码高尔夫球.

By messing up the code further (iterating over line with String.indexOf / String.substring) you can get it down to about 0.1 seconds quite easily, but I think I've answered your question and I don't want to turn this into some code golf.

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