stdin consumed where shouldn't

[kzidane]

A Scanner object may buffer all data in System.in, preventing subsequent Scanner(s) from accessing the rest of the lines (since they were consumed by previous Scanner), and therefore losing those lines. This can be replicated by redirecting stdin to a file.

http://stackoverflow.com/a/4232614/1797347

Foo.java:

import edu.harvard.CS50;

class Foo {
    public static void main(String[] args) {
        String s = CS50.getString("");
        while (s != null) {
            System.out.println(s);
            s = CS50.getString("");
        }
    }
}

data.txt:

foo
bar
baz

Output:

$ javac Foo.java
$ java Foo < data.txt
foo

[dmalan]

@kzidane, how about this?

https://github.com/cs50/libcs50-java/pull/18/commits/d8d023a7daae4c40ff1766fa5fec1ccb82b4e762#diff-acf6a41e9d226f255b68a55d3b0e193dR66

Since all get* methods call getString, seems okay to initialize Scanner once up top?

[kzidane]

I mean this still creates a Scanner instance unnecessarily if the user just imports edu.harvard.CS50, and never calls any of the get*, but probably nbd. Let's :shipit:!

On Sun, May 14, 2017, 6:45 PM David J. Malan notifications@github.com wrote:

@kzidane https://github.com/kzidane, how about this?

cs50/libcs50-java@d8d023a#diff-acf6a41e9d226f255b68a55d3b0e193dR66 https://github.com/cs50/libcs50-java/commit/d8d023a7daae4c40ff1766fa5fec1ccb82b4e762#diff-acf6a41e9d226f255b68a55d3b0e193dR66

Since all get* methods call getString, seems okay to initialize Scanner once up top?

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub https://github.com/cs50/libcs50-java/issues/17#issuecomment-301324573, or mute the thread https://github.com/notifications/unsubscribe-auth/AG5TA88hcB-4ggTz8eSVlTBWuW5f9hbvks5r5y-jgaJpZM4NaD32 .

[dmalan]

Just did a test, actually, and scanner should only be initialized if the class is actually referenced, not just imported!

[kzidane]

Ah, it seems to be instantiated when class is initialized per http://docs.oracle.com/javase/specs/jls/se7/html/jls-12.html#jls-12.4.1. Sorry I forgot! :innocent: