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

Question

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

Is there any faster way of doing this in Ja

Answer 1

You can read from System.in in a digit by digit way. Look at this answer: https://stackoverflow.com/a/2698772/3307066.

I copy the code here (barely modified). Basically, it reads integers, separated by anything that is not a digit. (Credits to the original author.)

private static int readInt() throws IOException {
    int ret = 0;
    boolean dig = false;
    for (int c = 0; (c = System.in.read()) != -1; ) {
        if (c >= '0' && c <= '9') {
            dig = true;
            ret = ret * 10 + c - '0';
        } else if (dig) break;
    }
    return ret;
}

In my problem, this code was approx. 2 times faster than using StringTokenizer, which was already faster than String.split(" "). (The problem involved reading 1 million integers of up to 1 million each.)