Re: Project5Read
In article <j8nc55hoi5gqse8maumm7adb5lmf7bamve@4ax.com>,
rossum <rossum48@coldmail.com> wrote:
On Thu, 09 Jul 2009 12:06:56 -0400, "John B. Matthews"
<nospam@nospam.invalid> wrote:
In article
<6ef5e6dd-0da7-45ac-85d7-548f119b29e3@t13g2000yqt.googlegroups.com>,
matt <mweppler@gmail.com> wrote:
With Project5Write I am creating binary data using writeUTF and
writeInt. When it comes to Project5Read I would like to read the
data using readUTF and readInt one record at a time. I thought the
while ((c = istream.read()) != -1) would accomplish this but what
I really need in the while loop is a way to read each record and
then go to the next and so on. I wish I could explain myself
better but at this point Im just unsure of a number of things with
programming.
Here is the dat file when opened with a text editor:
I was curious what a DataOutputStream looked like inside:
$ hd test.dat
[...]
Well, you _could_ catch the EOFException to exit the loop, but
that's considered bad form. If only DataInputStream had a way to
determine if there was more data "available", perhaps something
inherited from it's superclass:
<http://java.sun.com/javase/6/docs/api/java/io/FilterInputStream.html>
No joy. According to the Sun tutorials that standard way to detect
EoF is to catch an EoF exception.
http://www.j2ee.me/docs/books/tutorial/essential/io/datastreams.html
"Notice that DataStreams detects an end-of-file condition by catching
EOFException, instead of testing for an invalid return value. All
implementations of DataInput methods use EOFException instead of
return values."
The sample code looks like:
try {
while (true) {
price = in.readDouble();
unit = in.readInt();
desc = in.readUTF();
System.out.format("You ordered %d units of %s at $%.2f%n",
unit, desc, price);
total += unit * price;
}
} catch (EOFException e) {
}
Thank you for amplifying on this. I hate to use exceptions for flow
control, but this may be an exception [sic] to the rule. I would have
liked to use FilterInputStream's available() method:
DataInputStream dis = new DataInputStream( ... );
while (dis.available() > 0) { ... }
It works, but I see it's really only an estimate.
Clunky, but it looks like the only way to do it. Ugh. Now I know why
I usually use text streams rather than data streams.
Better to amend Project5Write to output the number of records in the
file and to use that to determine EoF.
This is appealing, if permitted to the OP.
--
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>