In the "Why didn't someone think of this sooner?" category,
JBrownie 1.2
Onyxbits has released JBrownie 1.2, a "a wrapper around the system default javac Java compiler, that monitors Java sourcecode and automatically recompiles any files found changed.
The focus of this tool is to assist software developers, who prefer to use a plain text editors over a resourcehungry IDE, but still want their code to be autocompiled on the fly without delay and without having to manually start javac over and over again. Checking for syntax errors becomes now as easy as just saving the file in question."
Java 6 or later is required. JBrownie is published under the Apache 2.0 license.