Re: Bytes coming through as -1

From:
dsjoblom@abo.fi
Newsgroups:
comp.lang.java.programmer
Date:
2 Aug 2006 09:04:16 -0700
Message-ID:
<1154534656.950579.176500@m73g2000cwd.googlegroups.com>
AndrewTK wrote:

I am trying to read binary data from a network input stream but am
having a hard time at it. Consider the following:

    public static void main(String[] args) throws Exception {
        ServerSocket serversock = new ServerSocket(1234);

        while(true) {
            try {
                Socket s = serversock.accept();
                test(s.getInputStream(), s.getOutputStream() );
            } catch(Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void test(InputStream in, OutputStream out) throws
IOException {
        byte[] trash = new byte[10];
        int rcount;
        while( (rcount = in.read(trash)) != -1) {
            for(byte b : trash) {
                if(b ==-1) {System.out.print(".");}
            }
        }
    }

So far straightforward. It reads from the input stream and discards the
bytes. It also prints a full stop each time it encounters a byte
/inside the buffer/ that comes through as -1.

In theory, this should never happen: if a byte is -1, it comes out of
the read() method as such, which is normally a flag for read(byte[],
int, int) to stop reading.


Note that the read methods return an int, not a byte. Java bytes are
signed, having a range of -128 to 127, so a value of -1 is a perfectly
good value for a byte read from a socket. For more info about
conversions between different types, see
http://java.sun.com/docs/books/jls/third_edition/html/conversions.html#5.1

Regards,
Daniel Sj=F6blom

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