Re: Searching a motivating example for upcasts

From:

Lew <noone@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 19 Dec 2010 16:55:41 -0500

Message-ID:

<ielv0u$gle$1@news.albasani.net>

Peter Duniho wrote:

That's a surprisingly absolute and close-minded statement, even for Usenet.

Personally, I find that it is useful even for local variables to
restrict the type in use. For example:

InputStream stream = new FileInputStream("foo");

This helps document in the code that, while the object is in fact a
FileInputStream, the code is intended only to use the functionality
available in InputStream.

Arne Vajh??j wrote:

I don't think that example is relevant.

I would expect Stefan to be perfectly aware of that type
of code.

It is very basic OOP.

The example he gave had an explicit upcast.

Since Java can do upcasts without an explicit cast operator, it is never
required and therefore always implicit unless for some reason you want to
document its existence. The effect of an implicit or explicit upcast is
precisely identical, so who cares which it is? To talk about one *is* to talk
about the other.

And whether that construct is useful is a lot more
questionable.

Since an upcast is always allowed, an explicit upcast is always redundant.

It doesn't make sense to ask about explicit upcast in isolation, because it is
the same as an implicit upcast in behavior. If there is any question about
the usefulness of an explicit upcast, I'd say no, it's not really ever useful
since other parts of the syntax make it clear if there's upcasting going on.
But it still is going on!

--
Lew
Ceci n'est pas une pipe.