One of the awesome things about dealing with open software is to be able to access to the source code. When you deal with complex systems (so, every fraking day normally) the worst thing are black boxes that you cannot see, check or change their inside. This black boxes use to be closed/privaty systems/libraries/whatever. Lucky we are, android is open source you can get the source easily with repo but for developing applications in eclipse you can just install Android sources plugin and that’s it, really nice.
http://adt-addons.googlecode.com/svn/trunk/source/com.android.ide.eclipse.source.update/