What’s the fastest way to read from System.in in Java?

Is there any faster way of doing this in Java?

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

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.

A small comparison:

Reading 17 megabytes (4233600 numbers) using this code

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

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);

took 0.7 seconds.

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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