Problem with simple read from standard input

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Jonathan - 17 Feb 2005 06:52 GMT

I havn't been using java for long, but I don't remember having a problem
with this before. I'm trying to do a simple read from the System.in, and for
some reason my BufferedReader.readLine() method returns instantly with a
null... it never actually prompts me for input. Why is this????

String cmd = "0";
System.out.print("Enter a command: ");
try {
BufferedReader readerIn = new BufferedReader(new
InputStreamReader(System.in));
cmd = readerIn.readLine();
} catch (IOException e) {
System.out.println("error occured");
}
System.out.println("Command entered was " + cmd);

//the above program prints "Enter a command: Command entered was null"

thanks
jonathan

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Jonathan - 17 Feb 2005 07:50 GMT

Just a followup. I am thinking that perhaps this problem is somehow caused
by my IDE, NetBeans? I'd still appreciate help/comments from anyone.

> I havn't been using java for long, but I don't remember having a problem
> with this before. I'm trying to do a simple read from the System.in, and for
[quoted text clipped - 16 lines]
> thanks
> jonathan

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Roland - 17 Feb 2005 10:47 GMT

> Just a followup. I am thinking that perhaps this problem is somehow caused
> by my IDE, NetBeans? I'd still appreciate help/comments from anyone.
[quoted text clipped - 22 lines]
>>thanks
>>jonathan

Netbeans 4 perhaps?

NB4.0 appears to have a problem with reading input from System.in when
the application is run from within NB. I'm not up to speed with Netbeans
(normally use Eclipse), but the help on "Output Window" mentions the
following:
<quote>
When you run a program that requires user input, a new tab appears in
the Output window. This tab includes a cursor. You can enter information
in the Output window as you would on a command line.
</quote>
This input tab, however, does not appear when I tried a program that
reads from System.in. Probably with the new build system of NB4 (using
Ant), input to commandline programs has become difficult, or maybe
impossible.

Someone with experience in NB4 maybe knows how to enter keyboard input
for a command line program. Otherwise, if Netbeans has support forums
(undoubtly they have), you might want to ask there.

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Regards,

Roland de Ruiter
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Jonathan Halterman - 17 Feb 2005 19:42 GMT

> > Just a followup. I am thinking that perhaps this problem is somehow caused
> > by my IDE, NetBeans? I'd still appreciate help/comments from anyone.
[quoted text clipped - 42 lines]
> for a command line program. Otherwise, if Netbeans has support forums
> (undoubtly they have), you might want to ask there.

Yes, it appears I wasn't going crazy and that this was indeed a bug in
NetBeans 4 apparently caused by Ant. It's disappointing though to see that
it doesn't seem to be taken very seriously.

jonathan

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Oscar kind - 17 Feb 2005 17:09 GMT

> I havn't been using java for long, but I don't remember having a problem
> with this before. I'm trying to do a simple read from the System.in, and for
> some reason my BufferedReader.readLine() method returns instantly with a
> null... it never actually prompts me for input. Why is this????

See the API docs for java.io.BufferedReader#readLine(), regarding the
return value:
    A String containing the contents of the line, not including any
    line-termination characters, or null if the end of the stream has been
    reached

It appears System.in has reached its end, which probably means it's
closed. Did you start the program that contains your code snippet from the
command line?

Also, I suggest you either bookmark the following link, or download the API
docs from Sun. It describes all standard classes, and what they do.

    http://java.sun.com/j2se/1.5.0/docs/api/index.html

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Oscar Kind http://home.hccnet.nl/okind/
Software Developer for contact information, see website

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Problem with simple read from standard input

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