Java scanner frustrations

Question

I have the following method:

private String doEntryScan(InputStream stream)
{
    try (Scanner scanner = new Scanner(stream)) // Reading from System.in
    {
        String readString = scanner.nextLine();
        if (readString.isEmpty())
        {
            readString = "\n";
        }
        scanner.nextLine(); //consume carriage returns if they remain
        scanner.close();
        return readString;
    }
}

The idea is that the user can hit enter to accept defaults. Or they can enter something. If I include the line

scanner.nextLine(); //consume carriage returns if they remain

the method hangs at that point, presumably waiting for more input. If I don't have that line, I get a NoSuchElementException the next time I call this method. I'm assuming this is because there's a carriage return in the stream.

So how does one get around this? scanner.hasNext() doesn't help because it ALSO "sometimes" blocks. By the way, in practice InputStream is System.in.

The try-with-resources **closes** `System.in` **and** so does `scanner.close();` So you are closing it *twice*. — Elliott Frisch, Feb 24 '17 at 17:10
You are. When you close a scanner pointing at System.in, you are also closing the stream. See http://stackoverflow.com/questions/14142853/close-a-scanner-linked-to-system-in — azurefrog, Feb 24 '17 at 17:10
ensure you have enough to consume with method like `if (scanner.hashNextLine())` before consuming from input source and remove close call on your scanner. — SMA, Feb 24 '17 at 17:12
oh goddamit java. just when I expect you to be reasonable. Thanks for the help! — Kevin Milner, Feb 24 '17 at 17:17
this was indeed the cause. Elliot or azurefrog, if you want to write an answer I'll accept it. — Kevin Milner, Feb 24 '17 at 20:03

Java scanner frustrations

0 Answers0