Android Export File Format?

We are working on a project with a client who is building a portion of an Android app using Unity. We have never used the platform before but they tell us they are going to export the app to Android? I’m assuming that means they will export it as a Java file? Then we can use eclipse to write in our part of the build?

I’m just not sure file formats Unity exports as

The final app will be in .apk file format. APK files are executable on Android devices.

Ahh so the platform does compress it into the apk… so they can’t send me the source code and we open it in something like eclipse? I assume your platform still has to use Java correct?