Thread: Reading a files header, hex

What code have you done so far. It would be easier to know what you are talking about with a "visual" of your process.

I have been able to print out the hex of a whole file but not managed to set a maximum read limit

It should be easy to stop reading on any given byte. Can you explain what the problem is with limiting the number of bytes read and displayed?

This ccoding gets all the hex of a file but its just the 47 49 46 38 that i want

Change the while loop to a for loop that loops 4 times.

Please edit your post and wrap your code with
[code=java]
<YOUR CODE HERE>
[/code]
to get highlighting and preserve formatting.

If a while loop that reads to the end of the file works for all the bytes in a file, replacing the while loop with a for loop can limit the number of bytes read and displayed.

problem is that i want to be able to open a file from a directory

Please explain what problem you are having? What does: from a directory" mean?
Are you having problems getting the path to the folder that contains the file?
Do you want the user to select it? See the JFileChooser class.

read the file's first four hex digits

Are you asking how to read the first 4 bytes of a file and convert each byte to a 2 character String of hex digits?


Is this related to: http://www.javaprogrammingforums.com...html#post99670

tried using a for loop on it so that it just loops to get the amount of bytes i want but ive had no luck with it,

Please post the code and explain what the problem with it was.

Can you isolate the code like the code in post#3 and post it here?

tried using a for loop on it so that it just loops to get the amount of bytes i want but ive had no luck with it,

Where is the for loop?

Do you know how to write a for loop that will loop 4 times? Try using that kind of a loop to read and reformat the bytes that are read from the file instead of a while loop that goes until the end of the file.

Completely replace the while loop with a for loop.

need the coding to read into the file and get the hex that tells us what the files type is

That should be a small method that reads the first few bytes of a file and returns them.

i need is to be able to put a string of hex that has been got from the file into the method

Same answer as above.

Where is the small method you have been working on to do this? All the code that has been posted has much more than is needed for reading the first few bytes of a file, formatting the bytes into a String and returning that String.


This thread is a continuation of your other threads:
http://www.javaprogrammingforums.com...ad-string.html
http://www.javaprogrammingforums.com...html#post99670

Please finish those other threads and don't start new ones for the same topic.

The advice is the same as the last 3 or 4 times: use a for loop to read the first 4 bytes from the file.
Get rid of the while() loop!

Try writing the method in several steps:
1) write a loop to read bytes as int and display them
2) convert the ints to a hex string
3) concat the hex Strings
4)return the String

i have tried the for loop thing and it wont work,

Post the code with the for loop that won't work.

The steps the code should take for step 1:
loop 4 times
read next byte
if byte is -1 quit -> the file is too short
print the byte
end loop

//not sure what goes here

Inside the loop are these 3 steps:
read next byte
if byte is -1 quit -> the file is too short
print the byte

    if (i != -1) {

The loop control varialbe: i will never be -1. It will count the number of loops: 0,1,2,3

There needs to be a new int variable defined that will receive the byte that is read from the file.