Jay Edit

jEdit is a programmer's text editor developed by Slava Pestov and others. It is released under the GnuGeneralPublicLicense. It is a very good OpenSource editor (not just for JavaLanguage), that becomes an IDE in conjunction with the available plugins. jEdit requires Java 1.3 or greater.

jEdit has an easy to use interface that resembles that of many other Windows and MacOS text editors.

jEdit is extremely customizable, and has an extensive feature set, that includes, among other things:

Syntax highlighting for more than 50 file types
Auto indent with support for intelligent indent in Java, C and Python source
Search and replace with support for regular expressions, searching in multiple files, and reverse search
Bracket matching
Abbreviations
Multiple clipboards
Rectangular selection
Split-window operation
Word wrap
Macro recording
BeanShell scripting
Folding
Multiple selection (only in jEdit 3.2 or greater)

However, the feature list doesn't stop there; jEdit also supports plugins which extend the editor's functionality. Plugins currently exist for

editing files on FTP servers (and SFTP servers)
editing files inside zip and tar archives
browsing Java source
code completion
compilation
one-click compiler error go to
viewing RSS feeds
XML completion and validation (XmlSucks less with jEdit :-)
transforming XML with XSLT
checking spelling
bookmarking locations in files
embedded PythonLanguage interpreter
getting word definitions from online dictionaries
VersionControl integration for various systems
installing macros from an online user-contributed repository

and much more.

Plugins can be managed from within the editor.

http://jedit.org/

jEdit has a wiki: http://community.jedit.org/cgi-bin/TWiki/view/Main/ProgrammingJavaInJEdit