Hacking on JDK 1.5 Early Access

After reading Matt Quail’s blog entry on how horribly hard JDK1.5 will be, I downloaded the early access compiler and started hacking on it.

I played around with a few little programs, then got stuck into PragDave’s Kata 6—read a dictionary of words, find all the anagrams, and print them out.

Here is my code. It gives generics and the JSR-201 enhanced for loop a good work out. The other features—enums, autoboxing, meta-data and static imports—aren’t used.

Observations:

• Enhanced for loop is useful. It does away with the boiler plate for getting, testing and next()ing iterators.

• The generics enhancements are way cool. My program contains no casts, despite manipulating a Dictionary of Lists of Strings and a List of Lists of Strings

Digression on Variance

Java JSR-014 generics suffer from a problem. Joshua Bloch (quoted by Michael Coté) gives a good nutshell explanation:

An Integer is a Number, but a List of Integers is not a List of Numbers.

A solution to this problem is the experimental “variance” extension to generics, which ships with the early access compiler. These look really cool: there is little difference to users of the generic classes (except that more things ‘just work’¹), and they aren’t that much harder for writers of generic classes.

Frankly, programmers² will need to be discouraged from writing generic classes. They can be difficult to implement in a correct and maintainable fashion. The newly genericised java.util collections classes should be all the generics most of us need, most of the time.

Overall, I have to disagree with Matt. JDK 1.5 is a step forward. “The Masses” (as Matt refers to them) will find their day-to-day coding simplified³. “The Smart People” will need to learn a slightly bigger language—hardly a problem for them.

¹ Or, to put it another way, fewer things fail mysteriously.

² Especially the smart ones that assume that everybody else is as smart as them.

³ And day-to-day simplicity is good, especially in the face of things like this, this or this.