Developers, have I got a treat for you today: AIDE - Android Java IDE. AIDE is a self-contained integrated development environment that allows devs to write, compile, and run Android apps on their Android devices. Normally, if you want to write Android apps, you do it on a separate machine running Eclipse (or an alternative IDE). Now... well, you probably still do for major projects (especially ones involving complex library dependencies), but you can edit or create smaller ones without ever leaving the Android ecosystem.
AIDE really is more than just an editor - it supports code completion, real-time error checking and highlighting, code refactoring, formatting, and smart navigation, as well as compilation and execution of APKs.