Reg suffering from high-altitude hypoxia?

Respected Java and XML Guru Elliotte Rusty Harold has posted a very nice discussion of Eiffel's Design by Contract principles. Along the way, he makes a vicious ad hominem attack, accusing me of architecture astronautics (he actually stooped to using using the word "theorist," which means, someone who blogs when they should be coding). But I digress.



The gist of his post is that since we don't have language-level support for Design By Contract, we ought to use final to accomplish as much invariant enforcement as possible. He suggests that final should be the default choice, that interfaces should be rare and concrete classes plentiful in a design, and that support for polymorphism is less-important than enforcing invariants:

Preconditions, postconditions, and invariants are at the core of data encapsulation. They are the first and most important pillar of object oriented programming. Inheritance and polymorphism are second and third respectively, and are less important.

While controversial, this argument is cogent. I would say it is consistent with a specific kind of design philosophy, one that would be as at home in Ada or Modula as it is in Java. This is in marked opposition to the design philosophy of SmallTalk and Squeak, so I would say it is not very object oriented.

Is that a bad thing? I don't think so. Principles like data encapsulization, modularity, contract enforcement, and componentization are extremely valuable and can be realized in many different ways. For example, what do you think the Erlang programming language or the Linda communication and coördination frameworks are are all about? It's not just concurrency, dude.

The large-scale Java applications I've seen have been particularly devoid of true object orientation, and people seem perfectly happy with that. (Rough metric: the OO-ness of a Java application is congruent to the reciprocal of the number of public static methods in the source code).

So my conclusion is that if you want some advice on writing robust, large scale Java applications in a style that has been proven to be useful over the last several decades, you will find Rusty's post informative.

p.s. My tongue was in my cheek when I composed the title and suggested that one of the most socially conscious Java bloggers in the world was vicious. But you knew that.

p.p.s. If you feel that either Rusty or I can be correct but not both of us, please accept my condolences. How long has it been since imagination passed out of your life?

Labels: java

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