Tuesday, January 22, 2008

The taste of Java Generics

As the closure debate flames are rising, people are attacking Generics in order to attack closures. Some use it as a negative example against particular closure proposal, some try to discourage Java language changes in general and some to promote other languages. When I read articles that start with "Generics are hard" and lead into "Generics are bad", I can't help thinking of the fox and the grapes. Yeah, they are hard. So is concurrency, NIO and many other things. So? That's why people create frameworks on top of Java.

Don't get me wrong - Java Generics have faults, and they are long known. Here's a hit-parade of my biggest complaints, but I will also mention some solutions I have used:
1. Erasure
The way to work around it is by using type token or super-type token. As any workaround, it is limited, but it can solve part of the problem - Class#cast and Class#newInstance don't issue the annoying warnings.
2. Generic parameters not covariant
It is usually a good idea to use bound wildcards extensively.
3. No lower bounds support (except wildcards)
We can use static methods instead (ala extensions) with <T extends Super> rather than <S super Sub>
4. Verbosity, instead of more aggressive type inference
Not much to do, hm, learn to type faster? :-)
5. The angle brackets
Yeah, I hate them most when typing on blogger, luckily I am old enough to have been coding HTML in plain text editor a long time ago, so... back to GT and LT escapes.

BTW Java didn't die, it has simply grown beyond its hipness age. And I am glad that it spawned even better things, such as Scala. But there is a difference between "good" and "popular". Java is popular and not that bad, other languages may be better, but not as popular. Will Scala be willing to sacrifice some of its expressive power and shortcuts (gee, stuff like that reminds me why I don't code in Perl) to become simpler to learn/read and potentially more popular? Should it? (Ruby consciously didn't and ... didn't.) We shall see.


Anonymous said...

Return types of overridden methods are covariant.

In terms of overloaded methods' parameters, you can make them covariant with this tip.

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It seems that the type parameter cannot be used in the declaration of static variables or in static methods. Static variables and static methods are "outside" of the scope of the class's parameterized types.

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