When is a String not a String?

So I’ve been stumbling along writing this book and today I wrote some code where, rather than using good old Strings, I instead chose to use CharSequences. Why?

Well for one thing, I wanted to be able to process both Strings and StringBuffers alike and, thanks to JDK 1.4 and JSR-51, that’s possible as they both implement CharSequence- very nifty indeed. More importantly though, I wanted to be able to process data from files as well as in-memory.

Now, admittedly I could have written my code to process Readers or InputStreams instead and used a StringReader, etc. But really, when it came down to it, the algorithm I was writing suited strings and characters not bytes and buffers and all that hoo-ha and I wanted to keep it that way.

So, I thought to myself, I would do the opposite. I would write a CharSequence that wrapped a Reader. That shouldn’t be too difficult now should it? But then another thought occured to me. Before I leap into writing a whole bunch of code that I’d need to test and gasp maintain, maybe someone else had already done the hard work for me; maybe even the JDK!?

A quick flick of the wrist and IntelliJ brought up a class heirarchy for me and what do you know? along with String and StringBuffer was the little used CharBuffer from the NIO package. Another little present courtesy of the JSR-51 group.

A CharBuffer facilitates, among other things, memory mapped I/O, meaning you can address a file on disk as if it were a contiguous array of characters in memory. And, because it conveniently implements CharSequence, can be passed into my code just as any of the purely in-memory implementations.

The other thing I like about CharSequence is that it’s an interface. This makes it possible to decorate them and gather performance statistics really easily. Yes, yes, all you AOP weenies sit down and stop waving your arms about. I know your new (ok not so new anymore) fandangled whizzbang toy can do that too. But I don’t have to learn a new language or tools to do it. One day perhaps but not this one in particular. Believe me, my paradigm has been shifted quite enough and I’m giving it a rest for a while ;-)

The only thing missing is that, surprisingly, the Character class doesn’t implement CharSequence. I’m not sure how useful that really would be but I like the idea if only for completeness sake. It certainly wouldn’t be hard.

Anyway, I think I’ll be looking for opportunities to use my new best friend where I would usually have used a String. The only caveat is that a String is guaranteed to be immutable while a CharSequence isn’t. Oh and you can’t be guaranteed that equals will work between them either. No matter, I can still see the glint of those shiny golden nails from here :)