I've watched Scala off and on for years. Most recently, I've been toying with making a Scala-look-alike of my own, but far closer to Java. My two biggest problems with Scala have been these:
- Scala is very different from Java, even though you can code in Java style. I'm sometimes willing to learn new, but I've been afraid others wouldn't, and I wanted something with popular support. Also, it would be nice to be able to write Java libraries in "JavaNG".
- It has a 2.5 (plus or minus) MB runtime library. Some people couldn't care less, but I love small. To me, 2.5 MB isn't anywhere close to small. Oh, and then the compiler is 4 MB or so, if you want that.
Side notes, don't say "object Game extends JPanel" since the singleton objects create classes that make a static method for every method in the class or super class. Or at least all visible methods.
Also, even private vars create accessor methods. Closure vars don't, but they bring in the class IntRef (for ints). And simple closures like "(a) => a + 1" create a class with a half dozen methods defined in them. Maybe pack200 and gzip would take care of that, but pack200/gzip doesn't count for the Java 4K Game contest. In real life, it could be useful, though.
Oh, and I definitely used ProGuard.