Because it's written in Tcl/Tk, I found it very easy to
extend august, making the file dialog, for example, look for files
ending in .java first.
J provides another handy editor that also runs on Windows, available
from http://armedbear.org/. J, as you'd probably guess, is written in
Java, and it provides an interface very much like the Windows editor
TextPad, including a side window listing all the files you currently
have open. J seems to run well on Linux, with a more than acceptable
performance. This can be an issue with Java programs, because the Linux
performance of Swing, the Java graphical toolkit, has often been
bemoaned. I've been running j from the IBM 1.1.8 Java runtime and the
Sun Swing library with no problems.
There's no one true editor that works well for everyone. There are
plenty of editors available on Linux, though, so you should be able to
find one that meets your needs.