open "yes" and try to wait for it to finish

POpen.java

// According to http://git.savannah.gnu.org/cgit/coreutils.git/tree/src/yes.c,
// yes is supposed to exit when writing to its stdout stream returns EOF. So
// why does this program hang on #waitFor?

import java.io.InputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class POpen {
    public static void main(String[] args) {
        try {
            Process p = Runtime.getRuntime().exec("yes");
            InputStream s = p.getInputStream();
            BufferedReader r = new BufferedReader(new InputStreamReader(s));

            for (int i = 0; i < 5; i++) {
                System.out.println(r.readLine());
            }

            s.close();
            p.getErrorStream().close();
            p.getOutputStream().close();
            int result = p.waitFor(); // hangs here, why?
            System.out.println("exit: " + result);
            System.exit(result);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}