Programming Android

Chapter 3. The Ingredients of an Android Application

Based on the foundation laid in the last chapter for writing robust Java code, this chapter introduces the major high-level concepts involved in programming for the Android platform.

Traditional Programming Models Compared to Android

When starting applications, operating systems traditionally use a single entry point, often called main, which might parse some command-line arguments and then proceed to execute a loop that would read user input and produce output. The OS would load the program code into a process and then start executing it. Conceptually, this kind of process would look something like Figure 3-1.

Figure 3-1. A simple application in a process

With programs written in Java, it gets a little more complex: a Java virtual machine (VM) in a process loads bytecode to instantiate Java classes as the program uses them. This process looks something like Figure 3-2. If you use a rich graphical user interface system like Swing, you might start a UI system and then write callbacks to your code that process events.

Figure 3-2. A Java application, running in a Java virtual machine, in a process

Android introduces a richer and more complex approach by supporting multiple application entry points. Android programs should expect the system ...