The official language for Android development is Java. Large parts of Android are written in Java and its APIs are designed to be called primarily from Java. It is possible to develop C and C++ app using the Android Native Development Kit (NDK), however it isn't something that Google promotes

Unfortunately, learning to develop for Android is actually one of the trickier places to start. Building Android apps requires not only an understanding of Java (in itself a tough language), but also project structure, how the Android SDK works, XML, and more.

As the first course in the Android Developer Nanodegree, Developing Android Apps is the foundation of our advanced Android curriculum. In this course, you'll work with instructors step-by-step to build a cloud-connected Android app, and learn best practices of mobile development,and Android development in particular.

Mobile app development is an exciting career choice. The demand for apps is accelerating and technology is ever-advancing. Not only do app developers work for small, medium and large-sized companies, but on freelance basis as well.

At this point, you could theoretically build native Android apps without learning any Java at all. The summary is: Start with Java. There are much more learning resources for Java and it is still the much more widespread language

The user interface (UI) for an Android app is built as a hierarchy of layouts and widgets. The layouts are ViewGroup objects, containers that control how their child views are positioned on the screen. Widgets are View objects, UI components such as buttons and text boxes.

An Android activity is one screen of the Android app's user interface. In that way an Android activity is very similar to windows in a desktop application. An Android app may contain one or more activities, meaning one or more screens

Is it possible to create a Android activity without UI? Yes it is. Android provides a theme for this requirement.