Though my tip though for the long term replacement of javac is Scala. I'm very impressed with it! I can honestly say if someone had shown me the Programming in Scala book by by Martin Odersky, Lex Spoon & Bill Venners back in 2003 I'd probably have never created Groovy. So why Scala? Scala is statically typed and compiles down to the same fast bytecode as Java so its usually about as fast as Java (sometimes a little faster sometimes a little slower). e.g. compare how well Scala does in some benchmarks with groovy or jruby. Or this. Note speed isn't everything - there are times when you might want to trade code thats 10x slower for more productivity and conciseness; but for a long term replacement for javac speed is important.
His dissatisfaction with Groovy concerned more than just its speed, and originated much earlier, see his very last Groovy mailing list posting [2] in Dec 2005 just before he left the Groovy development team:
The MOP and introspection APIs do NOT solve the horribly broken name resolution rules in the current RI of Groovy [...] I see no argument yet for why we have to throw away decades of language research and development with respect to name resolution across the language as a whole [...] It just feels totally wrong to break Closures across the entire language just because of some use cases for Markup.
Groovy is sloooooooow, its recent static typing is buggugguggy and not even used by Grails or Gradle, and its closures are broken. Its "recent surge in popularity" was also probably based on deception [3]:
Groovy, which turned up in the [Tiobe] 18th spot last month [October 2013], slid back down to a number 32 ranking [Nov 2013]. "After a long discussion with one of the Tiobe index readers, it turned out that the data that is produced by one of the Chinese sites that we track is interpreted incorrectly by our algorithms. So this was a bug," Janssen said. "After we had fixed this bug, Groovy lost much of its ratings." The ratings slip takes Groovy from a 0.658 percent rating last month to 0.393 percent this month.
This has happened before. In April 2011, Groovy fell from #25 to #65 on Tiobe in a single month after they increased the number of search engines they monitor. Groovy had begun its short-lived rise just after December 2010 when Groovy tech lead Jochen Theodorou "volunteered" his services to Tiobe to help them improve their algorithms.
[1] http://macstrac.blogspot.com/2009/04/scala-as-long-term-repl...
[2] http://groovy.329449.n5.nabble.com/Paris-write-up-tt395560.h...
[3] http://www.infoworld.com/t/application-development/c-pulls-a...
