Why does hasNextLine() never end?

java java.util.scanner
Helgi picture Helgi · Apr 13, 2011 · Viewed 23k times · Source

Sorry if this sounds too simple. I'm very new to Java.

Here is some simple code I was using to examine hasNextLine(). When I run it, I can't make it stop. I thought if you didn't write any input and pressed Enter, you would escape the while loop.

Can someone explain to me how hasNextLine() works in this situation?

import java.util.*;

public class StringRaw {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNextLine()) {
            String str = sc.nextLine();
        }
        System.out.print("YOU'VE GOT THROUGH");
    }
}

Answer

Lawrence Dol picture Lawrence Dol · Apr 13, 2011

When reading from System.in, you are reading from the keyboard, by default, and that is an infinite input stream... it has as many lines as the user cares to type. I think sending the control sequence for EOF might work, such as CTL-Z (or is it CTL-D?).

Looking at my good-ol' ASCII chart... CTL-C is an ETX and CTL-D is an EOT; either of those should work to terminate a text stream. CTL-Z is a SUB which should not work (but it might, since controls are historically interpreted highly subjectively).

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