Re: Java language and library suggestions

From:

Tom Anderson <twic@urchin.earth.li>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 20 Jul 2009 08:44:45 +0100

Message-ID:

<alpine.DEB.1.10.0907200841370.15895@urchin.earth.li>

On Sun, 19 Jul 2009, Arne Vajh?j wrote:

Tom Anderson wrote:

On Sun, 19 Jul 2009, Arne Vajh?j wrote:

Tomas Mikula wrote:

The designer of the API may as well state that the declared exception
will only be thrown under certain circumstances. If I avoided these
circumstances, then the exception won't be thrown. I will provide an
example:

class WriterEncoder {
   public WriterEncoder(Writer w);

   /** @throws IOException if and only if the write() methods of
underlying Writer throw an exception. */
   public void writeEncoded(MyClass obj) throws IOException;
}

Now if I construct the WriterEncoder with StringWriter which does not
throw IOException on write, I can be sure that
WriterEncoder.writeEncoded() won't throw IOException either.

Yes.

But it is very bad code.

The safe construct is relying on knowledge about implementation of both
the calling and the called code instead of just relying on the exposed
API's.

But this is complete nonsense! That example DOES only rely on the exposed
APIs!

No.

It relies on:
1) that it is indeed a StringWriter and not another writer that gets
passed in as argument
2) that writeEncoded only throws IOException if the passed Writer
throws IOException.

Bad code.

Every, *every*, line of code you write relies on the lines of code right
before it. That's how code works. Your argument is utterly specious.

WriterEncoder.writeEncoded's API specifies that it throws the same checked
exceptions as the writer's write method.

No it does not.

WriterEncoder.writeEncoded's API specifies that it throw IOException. It
does not say anything about when it does it.

Flat out wrong. From the code above:

/** @throws IOException if and only if the write() methods of underlying Writer throw an exception. */

Anyway, i don't think there's any point in us arguing about this any more,
because we're clearly living in different universes. Have a good week!

tom

--
a blood-spattered Canadarm flinging goat carcasses into the void