Re: Printing only an 'A' to System.out

Eric Sosman <>
Wed, 22 Apr 2009 11:24:12 -0400
Stefan Ram wrote:

 [... is a '\n' required at the end of every text output line? ...]

  Now, my question regarding Java: Is anything wrong with
  the following Java program?

public class Main
{ public static void main( final java.lang.String[] args )
  { java.lang.System.out.print( "A" ); }}

  The output might look ugly, because it might not be separated
  from text following it properly, but is there a wording
  similar to ISO/IEC 9899:1999 (E), 7.19.2#2 somewhere in a Java
  specification that might condemn this program in a similar
  manner to ISO/IEC 9899:1999 (E), 7.19.2#2?

  (7.19.2 is in C because the I/O facilities offered by the
  environment (operating system) might require a terminating
  linefeed. If a Java implementation is running in the same
  environment, it should inherit the same limitations from the
  same environment. So, if Java guarantees that the last line
  never requires a terminating new-line character, how does it
  do that? [One answer would be: by excluding those environments
  that require a terminating new-line character.])

     Perhaps someone can find a more definitive answer, but it seems
to me that the question comes down to the behavior of the flush()
method of whatever OutputStream subclass ultimately underlies the
PrintStream. The Javadoc for OutputStream#flush() says

    If the intended destination of this stream is an abstraction
    provided by the underlying operating system, for example a
    file, then flushing the stream guarantees only that bytes
    previously written to the stream are passed to the operating
    system for writing; it does not guarantee that they are
    actually written to a physical device such as a disk drive.

 From this, I'd say that if the platform requires a trailing '\n' and
you don't write one, you're on shaky ground. Perhaps the platform
will synthesize a '\n' for you, or perhaps it will just lose the final
line of output. And the behavior may vary depending on the nature of
the destination: Files, pipes, sockets, and printers might all behave
idiosyncratically in the absence of the '\n'.

     Maybe a less roundabout (or even contradictory) answer exists
somewhere, but I haven't found it.


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