Tuesday, February 17, 2009

Crazy Java Puzzler

Here is a puzzle for you. As the title promises, yes, it's quite crazy. It is assumed that you already are a die-hard Java programmer that knows the language better than the skin of his very palm. Ok, maybe not that much, but anyway.

As a little history, I had posted this on the Hellenic (i.e. Greek) Java User Group, which used to have an online forum, now defunct (too bad). So if you happen to be on those few who happened to see the solution there, just restrain yourself, I don't want any stinkin' spoilers!

Enough of intro. Here is the code:

interface id {
  <id> Void read(List<id> list);
  <id> Void read(List<id> list);
  <id> Void read(List<id>... list); //*

The puzzle: What is the shortest edit (measured in inserted/deleted characters) that makes this program compilable? (While keeping the read methods overloaded).

(We're not talking any kind of cheat like compiling with some arbitrary compiler, just the plain Java compiler. Oh, and commenting out lines of code is the wrong answer too).

The problem, obviously, is that the two methods produce a name clash.Well, it's all yours! Hit it hard! Can you nail it?

* [10-Mar-10] As Sureth below points, a solution would be appending "[]" to a list, a 2-character ending. Indeed. Sloppy of me. That basically ruins the fun, so I have to this third overloading to avoid [] and varargs solutions. Now (hopefully) only the intended solution is there, hopefully in not too artificial a puzzle. Oh, by the way, trying this problem is not a waste of time: it reveals a deeper knowledge about the java platform and gives a new (for those unaware of it) technique that can be used in API design. It's already the "magic sauce" of the nice API of a popular testing-related framework.