XOM API for Processing XML with Java

[Elliotte Rusty Harold <elharo AT metalab.unc.edu>]

At 9:38 AM -0800 11/28/02, Edwin Goei wrote:

> 2) XOM does not allow method call chaining
>
> 3) JDOM: Setter methods don't return void


Setter methods should return void. Partially, this is based on my 
experience with JavaBeans, where returning void is necessary for a 
method to be recognized as a property setter. However, more 
importantly, it's semantically the right thing to do. By invoking a 
setter method (or any adder or mutator method) you are changing an 
existing object. You are not creating a new object. You are not 
getting a reference to some value that you did not have before. 
Nothing has been created that did not exist before. There is no 
justification for returning anything.

This naturally prevents method chaining, but perhaps this is a good 
thing. I find long strings of method chains to be ugly and 
unreadable. For example, consider this JDOM code:

(new Element("word")).appendChild("d").appendChild("o").appendChild("g");

Does this create <word>dog</word> or <word>god</word>? How sure are 
you of your answer? What if the middle method call throws an 
exception? What state is the object left in? Again, how sure are you 
of your answer?

Dividing this statement up into multiple relatively atomic operations 
makes the code cleaner, easier to read, easier to understand. Yes, 
there are classes in the Java class library that don't operate this 
way, most notably StringBuffer. Perhaps this makes sense for 
StringBuffer, where it's basically the equivalent of the + operator. 
Honestly though, this is really just a sop thrown to performance to 
avoid allocating lots of extra strings. Logically, the plus operator 
should do what it does for numbers: return a new object that is 
neither of its operands.

There is simply no logical justification for a setter or mutator 
method returning the object itself. It is a crutch designed to 
support a particular programming idiom, but that idiom is neither 
necessary nor helpful. Method call chaining is not an improvement.
--

+-----------------------+------------------------+-------------------+
| Elliotte Rusty Harold | elharo AT metalab.unc.edu | Writer/Programmer |
+-----------------------+------------------------+-------------------+
|          XML in a  Nutshell, 2nd Edition (O'Reilly, 2002)          |
|              http://www.cafeconleche.org/books/xian2/              |
|  http://www.amazon.com/exec/obidos/ISBN%3D0596002920/cafeaulaitA/  |
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