Close a Scanner linked to System.in

Question

I have a Scanner linked to System.in. Now, after using the Scanner, I should close it, as it is bad coding practice to leave it open.

Answer 1

One option is to wrap your System.in stream in a CloseShieldInputStream that prevents it from being closed. Your reader would then use the CloseShieldInputStream rather than the raw System.in stream.

Here is the API for the class: http://commons.apache.org/io/apidocs/org/apache/commons/io/input/CloseShieldInputStream.html

Answer 2

Instead of adding shield classes and stuff like that, just put a nice comment and a

        @SuppressWarnings("resource")

That's good enough. And I don't seem to see a lot of drawbacks to this approach. Don't forget the comment.

Answer 3

According to the API for InputSteam "The close method of InputStream does nothing.", so since System.in is an instance of InputStream, you don't need to worry about close() being called on it.

Answer 4

I have vague memories of strange, undiagnosable problems long ago with using the same Scanner of System.in twice, so this is what I use (even though you should probably just use one scanner for the duration of the program):

static String input() {
    try {
        return new Scanner(System.in).nextLine();
    } catch (NoSuchElementException e) {
        throw e;
    }
}

For some reason this works without warnings, whereas if I don't do the catch-throw, Eclipse will complain Resource leak: '<unassigned Closeable value>' is never closed.

Answer 5

The simplest thing is to not close Scanner if you don't want to close the underlying stream.

Ideally you should create just one Scanner which you use for the life of the program. In any case, it appears you don't have a good reason to close it.