IntelliJ does actually have a "REPL" built in. Although lately, I've simply been using the Scala REPL and/or Clojure+Slime to verify whether a Java library work

IntelliJ does actually have a "REPL" built in. Although lately, I've simply been using the Scala REPL and/or Clojure+Slime to verify whether a Java library works the way I expect it to. (I also use "perl -d" as a REPL for Perl, which it does quite well)