Re: MappedByteBuffer and corrupted data
- From: Daniele Futtorovic <da.futt.newsLOVELYSPAM@xxxxxxxxxxx>
- Date: Sat, 16 Feb 2008 07:21:12 +0100
On 2008-02-15 15:24 +0100, Daniele Futtorovic allegedly wrote:
On 2008-02-15 09:22 +0100, John allegedly wrote:Hi, i've been experiencing somme corruption of data with MappedByteBuffer. My serialisations are pretty simples. I've put "magic" byte for the debug, and some time, the byte i read is not equal to the "magic" value.
So i'm wondering if somebody has already experienced this kind of troubles. If it's not a bug in Java, what can it be ?
TIA
Post a code example (sscce) if you want precise answers.
As a guess, it might be you're trying to compare signed bytes with unsigned byte values and get entangled in promotions and widening conversions. Careful addition of 0xFF masks might solve it.
To illustrate my point:
public static void main(String[] ss) {
int MAGIC = 0xFA;
byte b = (byte) MAGIC;
System.out.println(b == MAGIC);
System.out.println((b & 0xFF) == MAGIC);
}
Yields:
false
true
Likewise:
public static void main(String[] ss) throws Exception {
final byte MAGIC = (byte) 0xFA;
PipedOutputStream pos = new PipedOutputStream();
PipedInputStream pis = new PipedInputStream(pos);
pos.write(MAGIC);
int read = pis.read();
System.out.println(read == MAGIC);
System.out.println(read == (MAGIC & 0xFF));
}
Yields:
false
true
Conclusion: Mind two's complement arithmetic, especially when doing IO!
In Java, bytes are signed, but the "bytes" you read off an InputStream
are unsigned.
df.
.
- Follow-Ups:
- Re: MappedByteBuffer and corrupted data
- From: pcspecialist9@xxxxxxxxx
- Re: MappedByteBuffer and corrupted data
- References:
- MappedByteBuffer and corrupted data
- From: John
- Re: MappedByteBuffer and corrupted data
- From: Daniele Futtorovic
- MappedByteBuffer and corrupted data
- Prev by Date: Re: What are the difference between Descriptor and Signature
- Next by Date: Re: HashMap vs linear table lookup
- Previous by thread: Re: MappedByteBuffer and corrupted data
- Next by thread: Re: MappedByteBuffer and corrupted data
- Index(es):
Relevant Pages
|
|
