This post and the plugin is outdated. Please use plugin from this link which is updated and allows customization of shortcut key mappings and much more.
Notepad++ is a great free editor. I like notepad++ because its a light weight editor and loads instantly. I use notepad++ for editing many files everyday. One plugin I always wanted was a plugin which lets me compile my java files and execute them from editor itself, but I couldn't find it so I wrote a myself. This plugin can be downloaded from this link.
I am working on this plugin to make it more effective, so that if user have more than one installations of JDK or JRE then user should be able to choose which one to use etc.
This is a simple plugin which has two commands-
Compile - compiles a java file.
Run - executes a java file.
For using this plugin Java must be installed on the system.