What does scanner.close() do?

Question

Say I have the following example code:

Scanner scan1 = new Scanner(System.in);    // declaring new Scanner called scan1
int x = scan1.nextInt();    // scan f         


        

Answer 1

Yes, it does mean that System.in will be closed. Test case:

import java.util.*;

public class CloseScanner {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        scanner.close();
        System.in.read();
    }
}

This code terminates with

$ java CloseScanner 
Exception in thread "main" java.io.IOException: Stream closed
    at java.io.BufferedInputStream.getBufIfOpen(BufferedInputStream.java:162)
    at java.io.BufferedInputStream.fill(BufferedInputStream.java:206)
    at java.io.BufferedInputStream.read(BufferedInputStream.java:254)
    at CloseScanner.main(CloseScanner.java:7)

Once closed, you won't be able to use System.in for the rest of your program. The fact that close() is passed through is nice because it means you don't have to maintain a separate reference to the input stream so that you can close it later, for example:

scanner = new Scanner(foo.somethingThatMakesAnInputStream());

You can do that and call .close() on the scanner to close the underlying stream.

In most cases you won't want to close System.in, so you won't want to call .close() in that case.