Check if the user is typing in the console window

Question

Is there a way to check if the user is typing in the console window in Java?

I want the program print whatever I type if I type something, otherwise print out "No input".

The tricky part is I want the program keep looping and printing out "No input", and then when I type "abc", it would immediately print out "abc".

I tried to use Scanner to do this as:

Scanner s = new Scanner(System.in);
while(1){
    if(s.hasNext()) System.out.println(s.next());
    else System.out.println("No input");
}

But when I ran it, if I did not type anything, the program just stuck there without printing "No input". Actually, "No input" was never printed.

Something along these lines: http://stackoverflow.com/questions/9545388/how-can-i-detect-arrow-keys-in-java-console-not-in-gui — Darius X., Mar 06 '15 at 12:57
while (1 ) ... how is 1 a condition? Against what are you comparing it? — Stultuske, Mar 06 '15 at 12:57
if its java, your code wont compile, while(1) is invalid syntax — user902383, Mar 06 '15 at 12:58
Yeap, while(1) works for C/C++ but in java you need to put while(true) — Razib, Mar 06 '15 at 12:59
Sorry, I wrote it wrong, it should be while(true). But it does not matter, after changing, it's still not working! — Michelle, Mar 07 '15 at 01:06

score 1 · Answer 1 · answered Apr 27 '15 at 19:56

From a command line, I see no chance to receive the input before hitting the "enter button". (unlike "onKeyDown/Up")

But considering & accepting this restriction, a simple solution is to use Reader.ready():

(..returns) True if the next read() is guaranteed not to block for input, false otherwise.

import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.util.Scanner;

public class Solution {

    public static void main(String[] args) throws IOException {
        final Reader rdr = new InputStreamReader(System.in);
        final Scanner s = new Scanner(rdr);
        while (true) {
            if (rdr.ready()) {
                System.out.println(s.next());
            } else {
                // use Thread.sleep(millis); to reduce output frequency
                System.out.println("No input");
            }
        }
    }
}

Check if the user is typing in the console window

1 Answers1