Code Safety and Pedantry

Jun 3, 2016 10:23 AM

Tags: java

Lately, I've been musing a lot on the topic of code "correctness" - that is, beyond the normal case of wanting code to do what I intended, and further into the realm of sweating even extremely-miniscule details. A lot of this is due to my continued watching of the evolution of Apple's Swift language (I highly recommend following Erica Sadun's blog for this). Swift is very much in the camp of "make sure all your 'i's are dotted and 't's crossed" languages, as opposed to more fast-and-loose languages like JavaScript or Ruby.

I've gone back and forth on the overarching concepts from time to time. I've long been a big Ruby fan, and a lot of that is because of a general feeling that, if you let go of a lot of the "strict old aunt of a compiler" restrictions, you gain a tremendous amount of expressiveness and productivity with few real-world problems. On the other hand, being immersed in Java all the time has shifted my brain to appreciating the benefits of stronger compile-time checks (at least on paper). Overall, I'm more on the latter side than the former now, double-edged sword though it is. This is why I've been diving into things like aggressive null analysis in my code. Even when it seems like it's being a pedant, there are certain classes of bugs that it finds that I wouldn't even normally think of on the fly. For example, the null checker flags this as being a potential NPE:

if(this.foo != null) {
	this.foo.doSomething();
}

My first reaction upon seeing that was along the lines of "you're full of crap, Eclipse", but then I noticed the small path a bug could take to creep in: multithreading. If I'm in a situation where the object containing foo is used across threads, there's a possibility where Thread A would evaluate this.foo != null to true and start to step in to the block. Then, Thread B would get its turn on the processor and evaluate this.foo = null in another method. Thread A would then pick up and try to call doSomething() on the newly-minted null. So I've swallowed my pride and started writing safer code like:

SomeObject localFoo = this.foo;
if(localFoo != null) {
	localFoo.doSomething();
}

What I've always admired about Swift is that it takes these sorts of lessons to heart and adapts the syntax to suit. My interest in code-correctness pedantry in Java has led me to write out verbose abominations like this:

private final @NotNull String foo;

Three of the conceptual tokens there are purely to say things that are best practices to start with: I don't want this property accessible outside the class, I want to make sure it's assigned during construction and not change thereafter, and I want to ensure it's not null. The Swift variant is:

let foo: String

Same thing, half the typing. And, as a bonus, since nullability checking is built in to the language and not a by-convention thing like the null annotations in Java, I can be sure that the rules will be applied. That sort of thing is the dream! But, since Java is the best language for the work I'm doing for now, the important thing is that it at least suits, verbose or not. In a lot of languages, it gets much more difficult to have this sort of assurance.

So, hassle as it is, I suggest that other Domino developers, on their paths through Java, consider picking up the same habits. For every time you run into something like Java complaining that it can't convert a List<String> into a List<Object>, diving fully into null checks and immutability will save you a late-night crash report and angry user. As you develop more in Java, give it a try.

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