Re: Exception Names

From:

Tom Anderson <twic@urchin.earth.li>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 28 Mar 2009 14:49:43 +0000

Message-ID:

<alpine.DEB.1.10.0903281439430.19324@urchin.earth.li>

On Fri, 27 Mar 2009, Thomas Pornin wrote:

According to Tom Anderson <twic@urchin.earth.li>:

InputStream.read should throw an EOFException instead of returning -1
at the end of a stream.

There are two kinds of conceptual "read" operations on a stream. One is
some kind of "get me the next byte(s), or end-of-stream, whichever comes
first". The other is more on the lines of "get me the next byte, which
had better be present, because it is expected, and early EOF is an
error". A single read() method cannot implement both semantics
simultaneously.

I'm going to repeat what i said about maps, and point out that:

int nextByte = in.read();
if (nextByte != -1) {
handleByte(nextByte);
}
else {
handleEnd();
}

Can trivially be rewritten as:

try {
int nextByte = in.read();
handleByte(nextByte);
}
catch(EOFException e) {
handleEnd();
}

Or another common idiom:

int nextByte = in.read();
if (nextByte == -1) {
handleEnd();
return
}
handleNextByte(nextByte);

try {
int nextByte = in.read();
handleNextByte(nextByte);
}
catch (EOFException e) {
handleEnd();
return;
}

Sun could possibly add some readFully() methods to InputStream, such
as:

    public int readFully()
        throws IOException
    {
        int x = read();
        if (x < 0)
            throw new EOFException();
        return x;
    }

    public void readFully(byte[] buf)
        throws IOException
    {
        readFully(buf, 0, buf.length);
    }

    public void readFully(byte[] buf, int off, int len)
        throws IOException
    {
        while (len > 0) {
            int rlen = read(buf, off, len);
            if (rlen < 0)
                throw new EOFException();
            off += rlen;
            len -= rlen;
        }
    }

but with some extra thinking about what should be done with
multi-threaded access, and possibly some prior checks on provided array
offsets and lengths.

These methods are already in DataInput(Stream):

http://java.sun.com/javase/6/docs/api/java/io/DataInput.html#readByte()
http://java.sun.com/javase/6/docs/api/java/io/DataInput.html#readFully(byte[])
http://java.sun.com/javase/6/docs/api/java/io/DataInput.html#readFully(byte[],%20int,%20int)

So i suppose that if i had a burning desire for them, i could just wrap my
stream in a DataInputStream.

However, it is somewhat delicate to add such methods to InputStream
because there are many projects out there which extend InputStream and
may have added methods named readFully(). Source-code compatibility may
be altered.

Oh yes - it's definitely far too late to add these methods to existing
classes. I'm just moaning about them not being there from the start.

tom

--
Hesgadin. It was in two parts - both of them silent. I remember this map
came with a letter accusing me of stealing eggs. I had never understood
the relationship of the map to the accusation. I still don't, but I'm
grateful for the map.