Problems reading from binary file or creating it

Question

When I create the file I use the dataoutputstream to write one 'int' at a time:

Database.write(0)

Of course it doesn't say 0 it's a variable there but I printed it and the first one is 0 so I'm taking that one as an example.

Now I'm not 100% sure, but only using that line of code my file should now contain:

0000 0000 0000 0000 0000 0000 0000 0000

right?

So when I'm trying to read the very first 4 bytes using:

RandomAccessFile raf = new RandomAccessFile("Database", "r");
raf.seek(0);

byte[] ByteArr = new byte[4];
raf.read(ByteArr, 0, ByteArr.length);

ByteArr should contain just 0's?

Well I printed the Byte[] and this is what I get:

Kind Regards Captain Confused

score 2 · Accepted Answer · answered Sep 28 '13 at 01:55

2

The write() method writes a single byte to file. Its parameter is an int, but that int is assumed to be in the range [0, 255].

If you want to write a full 4-byte int to file, use the writeInt() method. Otherwise, to retrieve just the value 0 again, read one byte from the file using read().

As a side note, RandomAccessFile can handle both reads and writes, so you should use it for both.

answered Sep 28 '13 at 01:55

William Gaul

3,181
2
15
21

You were correct! When I hovered over write() in eclipse it said it took an int as variable so I misinterpret the meaning of it! On a side note I'll try using the RAF! Thanks – David Ekermann Sep 28 '13 at 02:04

score 1 · Answer 2 · answered Sep 28 '13 at 01:55

1

The problem is DataOutputStream.write(int b) actually only writes the least significant byte. If you want to write out 4 bytes you need to use DataOutputStream.writeInt(int)

answered Sep 28 '13 at 01:55

dkatzel

31,188
3
63
67

score 0 · Answer 3 · answered Sep 28 '13 at 01:55

You're writing something in Chinese and then trying to read it in English, of course it's not going to make sense. If you want to write using DataOutputStream, you must read using DataInputStream. As you see, a raw read won't understand the encoding that data streams use. Alternatively, you can read raw bytes, but then you'll have to write them as well, not use a DataOutputStream which encodes the data so that DataInputStream can decode it.

Problems reading from binary file or creating it

3 Answers3