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From: me@me
Subject: Re: Ada for numerics computation (i.e. forget Fortran ?)
Date: 1999/04/27
Message-ID: <7g4av3$bgd@drn.newsguy.com>#1/1
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References: <372083A1.45A5EB97@t-online.de>
 <7fqeua$ih8$1@pegasus.csx.cam.ac.uk> <8790bhslfz.fsf@bglbv.my-dejanews.com>
 <7fvbth$4m4$1@news.rz.uni-karlsruhe.de> <7fvpl8$mpm@drn.newsguy.com>
 <7g1e20$t12$1@wanadoo.fr> <7g1n08$8t8$1@news.rz.uni-karlsruhe.de>
 <7g1qcm$o4$2@pegasus.csx.cam.ac.uk>
Organization: Newsguy News Service [http://www.newsguy.com]
Newsgroups: comp.lang.ada
Date: 1999-04-27T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <7g1qcm$o4$2@pegasus.csx.cam.ac.uk>, mgk25@cl.cam.ac.uk says...
>

>The childish hype surrounding "Javajavajava" is what has most of all
>turned me a bit against this language. 

But hype sells !

I think the reason for Java popularity is that people in general were not
happy with C++ (too complicated, etc..) , and wanted a different OO 
language, and Java came at the right time, and it looked like C++ to 
keep the crowds happy.

One thing that I did not see many discuss about java, is its default use
of references.

What I do not like in Java, is that it is not 'value' based by default.

meaning, when I write (where A and B are objects):

A = B;

then I go and modify the value of object B in some other part of 
the program, this results in A's value also being modified.


This is a side effect of the fact that in Java, objects are references,
hence in the above assignment, A takes on the same reference as B, making
A and B references to the same 'object' data on the heap.

(In simpler terms, A and B point to the same object on the heap).

(this one time caused subtle a bug in one of my programs, when I started
learning Java, as I was used to value-based languages, untill I 
noticed this. I was 'saving' objects in a vector, then reading new values
into the source objects, but this was also causing the objects in the
vector to change indirectly).

To make A get its own value of the object B, one needs to be explicit and
write

A = B.clone();

(Assuming B supports the clone() method).

So, in Java, to get the value, you need to be explicit, else you get
the reference (pointer).

In Ada, (and C++), they are value based, i.e. the default in assignment
is to get the value of the object. If you need to get a reference, you
need to be explicit.

Some people might not consider this a big deal, and can get used to it
(as with LISP). For me, I find that I spend more mental energy while 
programming in Java for the above reason, to watch out for when I need
to use clone() or not. I do not have this problem with value based languages,
such as Ada.

What do you like more? or think is better, value-based assignments, or 
reference based?
(I assume you would prefer value-based if you are an Ada programmer).

me.