How to read byte correctly from file using Java RandomAccessFile?

I have a binary file with the byte 88 (which is 136 decimal).

I'm using Java's RandomAccessFile class and the "read" method to read this byte via a pre-defined buffer. I also tried "readUnsignedByte()" but get the same issue as below.

RandomAccessFile randomAccessFile = new RandomAccessFile(inputFile, "r");
byte[] headerBuffer = new byte[32];
randomAccessFile.read(headerBuffer);

The code above gives me -120 for 88, not 136.

I realize that the high-order bit or whatever is set, but I still need to be able to read the file and either get 88 or 136.

The issue is that this byte is the offset into the binary file where I can find the first record so a negative number won't work.

Would appreciate suggestions.

Thanks,

Just do b & 0xFF to convert it to positive integer.

You can use the Byte.toUnsignedInt method to convert a byte into an int in an "unsigned" way.

jshell> byte b = (byte) 0x88;
b ==> -120
jshell> Byte.toUnsignedInt(b);
$57 ==> 136

The operation is the same as b & 0xff but doesn't invoke magic numbers or knowledge about bitwise operators.

Issue with bulk-read

The method read(byte[]) you use for reading multiple bytes at-once actually reads a signed byte as in readByte(). Thus you're right, the first bit represents the sign and will thus be interpreted by Java potentially leading to negative number.

Use offset and read unsigned

Benefit of random-access is to jump to the position/offset in file using seek(long).
So, if you know the exact position of that record-pointer byte, you can jump there and proceed reading the desired byte as unsigned using readUnsignedByte().

See also

https://stackoverflow.com/questions/5144080/how-can-i-read-a-file-as-unsigned-bytes-in-java