Detecting eof

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jack.smith.sam@gmail.com - 11 Sep 2006 00:58 GMT

Hi All,

I am using this segment to read a file:

String str
while ((str=in.readLine()!=eof)

but I get error because of eof (I want to detect end of file). How can
I use it?
Also is there any way to detect blank lines in a file? for example:
a

b
If I read the second line is it equal to null or something elase?

Thanks for your help
Jack

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Lionel - 11 Sep 2006 01:05 GMT

> Hi All,
>
> I am using this segment to read a file:
>
> String str
> while ((str=in.readLine()!=eof)

What is /in/? BufferedReader? I suspect that you want to do:

while((str = in.readLine()) != null)

/in/ is not a very good variable name either.

> but I get error because of eof (I want to detect end of file). How can
> I use it?
> Also is there any way to detect blank lines in a file? for example:
> a
>
> b

Well str will equal the empty string "". Or, if the line is full of
spaces you can do str = str.stripWhiteSpace() to be sure that str is the
empty string. Then you do str.equals("") to find out if it is empty or not.

Lionel.

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Dale King - 12 Sep 2006 13:48 GMT

>> Also is there any way to detect blank lines in a file? for example:
>
> Well str will equal the empty string "". Or, if the line is full of spaces
> you can do str = str.stripWhiteSpace() to be sure that str is the empty
> string. Then you do str.equals("") to find out if it is empty or not.

The method you wanted is called trim, which removes leading and trailing
whitespace from the string.

Signature

Dale King

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rr news - 11 Sep 2006 01:09 GMT

Try this.

boolean eof;
eof = false;
try {
while (! eof) {
String str = in.readLine();
if (str == null) {
eof = true;
} else {
System.out.println(str);
}
}
} catch (Exception e) {
System.err.println ("Error: " + e.getMessage());
}

Signature

---------------------
Jason Herald
www.cingular.com

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Lionel - 11 Sep 2006 01:34 GMT

> Try this.
>
[quoted text clipped - 12 lines]
> System.err.println ("Error: " + e.getMessage());
> }

That while loop seems a whole lot uglier than:

String str;

while((str = in.readLine()) != null) {
System.out.println(str);
}

It's also easier to make a mistake in the body of the while-loop by
doing it that way.

Lionel.

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Arne Vajhøj - 11 Sep 2006 01:43 GMT

>> boolean eof;
>> eof = false;
[quoted text clipped - 21 lines]
> It's also easier to make a mistake in the body of the while-loop by
> doing it that way.

I would say that the last code is *the standard* way of
doing it.

Arne

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hiwa - 11 Sep 2006 01:54 GMT

Lionel のメッセージ:

> > Try this.
> >
[quoted text clipped - 25 lines]
>
> Lionel.

Yes, yours is the standard idiom for readLine() usage.
Beware, however, if the original resource has one or more non-canonical
line(s) which do not have a '\n' at the end, readLine() could block
forever or weird Exception could be thrown.

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Arne Vajhøj - 11 Sep 2006 01:59 GMT

> Lionel のメッセージ:
>>> boolean eof;
[quoted text clipped - 11 lines]
>>> System.err.println ("Error: " + e.getMessage());
>>> }

>> String str;
>>
>> while((str = in.readLine()) != null) {
>> System.out.println(str);
>> }

> Yes, yours is the standard idiom for readLine() usage.
> Beware, however, if the original resource has one or more non-canonical
> line(s) which do not have a '\n' at the end, readLine() could block
> forever or weird Exception could be thrown.

And your solution is different regarding readLine block
or exception how ??

Arne

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hiwa - 11 Sep 2006 03:31 GMT

Arne Vajhøj のメッセージ:

> > Lionel のメッセージ:
> >>> boolean eof;
[quoted text clipped - 27 lines]
>
> Arne

Oh no. Data canonicalization is often much more important than your
code issue.
I call them 'data bug' issue.

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Karl Uppiano - 11 Sep 2006 07:41 GMT

> Hi All,
>
[quoted text clipped - 13 lines]
> Thanks for your help
> Jack

Why not unconditionally spin in a loop and catch the EOFException to break
out?

Reply to this Message

hiwa - 11 Sep 2006 07:45 GMT

Karl Uppiano のメッセージ:

> Why not unconditionally spin in a loop and catch the EOFException to break
> out?

That should only works on some networking situation. It doesn't have
generality.

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EJP - 12 Sep 2006 08:24 GMT

> Why not unconditionally spin in a loop and catch the EOFException to break
> out?

Because it won't be thrown.

readLine() is defined to return null at EOF, not to throw an EOFException.

Reply to this Message

Lionel - 12 Sep 2006 23:47 GMT

>> Why not unconditionally spin in a loop and catch the EOFException to
>> break out?
>
> Because it won't be thrown.
>
> readLine() is defined to return null at EOF, not to throw an EOFException.

You could catch the NullPointerException :) . . . lol

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Detecting eof

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