The DataInputStream class seems appropriate.

Your description does not match:

(a)

(b)

(c)

(a) says you have fixed-length records, (b) suggests you have
variable-length records. What is it?

If you have binary fixed-length records, then RandomeAccess file might
be a good start for accessing and skipping records.

If you have binary variable-length records, a FileInputStream plus a
BufferedInputStream are a good start. Depending on the individual data
encoding, a DataInputStream might help, too. Or you need to program the
decoding by hand.

(a) says you have binaries, in (b) and (c) you seem to talk about text
files. What is it?

If you have indeed a text file, then FileReader and a BufferedReader are
a good start.

Clarify your requirements.

/Thomas

Take some time out to get your head properly around the difference between
textual information and binary data.  As a C (or C++) programmer, you have
probably spent your life thus far without having to consider the difference
between the two (assuming you use char, or unisgned char, for both).  In Java
the two are (correctly) not conflated, and you will /have/ to be aware at all
times which you are dealing with.

A recent thread, entitled "Strings and bindary data", (this will probably
wrap):
http://groups.google.co.uk/group/comp.lang.java.programmer/browse_frm/thread/1df
0f881855c6d8f
might be an effective starting point.  It contains an over-long post from
myself on the topic, plus -- probably more helpful -- several links to further
info.

Beyond that, it's simple as long as you keep your head straight.  Represent
binary data as binary (byte[] arrays, or ints, etc), and textual data as text
(Stings, char[] arrays, etc).  If the input is binary read it using a
ReadStream (or one of its variants), if it is textual use a Reader (or one of
the variants).  You can't easily mix the two, so if the data is actually mixed,
then read it as binary, treat it as binary while you identify the textual
subsequences, and then convert them to some suitable textual represention (for
which you will need to understand the basics of charsets/character
encodings/code-pages).

DataInputStream is occasionally useful, but not -- in my experience -- very
often.

   -- chris

   There are too many "ors" and "etcs." here for me to make much sense of
the nature of your files. If it's arbitrary binary data, what's wrong with
using java.io.FileInputStream to turn your file into a stream of bytes, and
working from there?

   I don't understand what you mean by "I'll need to find/recognize/skip
'\n' etc." Why would the '\n' character be treated specially in arbitrary
binary data? It's fixed length, so surely this character isn't acting as a
seperator, right?

   - Oliver