How Java and Android work

After we write a game in Java for Android, we click on a button in Android Studio to change our code into another form, a form that is understood by Android devices. We call this "other form" Dalvik EXecutable (DEX) code, and the transformation process is called compiling.

Compiling takes place on the development machine after we click on that button. We will see this work right after we set up our development environment in a minute.

Android is a complex system, but you do not need to understand it in depth, in fact, it is designed to hide the complexity, all operating systems are, and Android does this better than most.

The part of the Android system that executes (runs) our compiled DEX code is called the Dalvik Virtual Machine (DVM). The DVM itself is a piece of software that runs on a specially adapted version of the Linux operating system. So, what the user sees of Android, is, Android just as an app running on yet another operating system. Therefore the apps and games that we write are apps running on top of the app which is Android itself.

The purpose of the DVM is to hide the complexity and diversity of the hardware and software that Android runs on but, at the same time, its purpose is to expose all its useful features. This exposing of features works in two ways.

The DVM itself must have access to the hardware, which it does, but this access must be programmer friendly and easy to use. The way the DVM allows us access is indeed easy to use because of the Android Application Programming Interface (API).

This API is primarily designed to use with Java. In fact, most of the Android API, is itself, Java code. As I may have mentioned already, this makes Android games the most fun and thorough way to learn Android, Java and game development.

If you want to see the relationship between The Android API, DEX code, DVM and an Android device, look at this picture.

Let's set up Android Studio.