So, what is Android? How does one start developing for this platform? This masterclass introduces Android from a development perspective, and guides you to setup the development environment. In order to up hold the programmer’s tradition, we will build a “Hello World” application and run it in an emulator.

Android explained

Android is a platform designed for mobile devices that includes a customised Linux kernel, frameworks, libraries and commonly used applications. The Linux kernel manages the hardware and provides security, resource/file/process management, networking and drivers. A range of libraries sit on top of this kernel to provide functionality such as media playback, 2D/3D graphics, font rendering, data management, and web page rendering.

Figure 1: The Android software stack has a number of different components.

Android unlike most other mobile platforms is completely open, allowing complete access for anyone with the relevant programming skills to build and deploy applications. In fact you can deploy an application to your Android phone over a USB cable — no special permissions, certificates or extra rights needed. The freely available development kit provides full access to most of the hardware sensors and software libraries/frameworks that are part of the platform.

Developers have access to a powerful UI layout engine, a local database management system, a locale-aware resource manager for organising graphical/media/string assets, a notification manager to organise internal and external notifications, a powerful life cycle manager to manage the various processes created as part of an application, and an extensive graphics sub-system to build games. Here is a more in-depth description of the Android platform.

Android Device Hardware and the Interaction Model

Android devices have a minimum of 3 functional buttons unlike the iPhone, which has a single physical button. Android devices have a Home, Back and Menu button. The Home button returns the user to the main phone screen — it is very similar in functionality to the iPhone’s. The menu button permits contextual menus to be added to any screen. The Back button has functionality similar to the back button on a web browser, and takes the user back to the previous screen. In terms of usability, the back button is considered to be effective on a mobile device. Although many applications on Android make use of the Menu button, the options provided in this menu need to be discovered by the user — they literally have to press the menu button on the various screens of an application in order to find the options available within the contextual menus.

The Android platform permits hardware vendors to create additional buttons including keyboards and have different form factors with screens of different sizes — there are even differentiations in terms of the availability of the sensors. This rather generous policy has resulted in the hardware vendors creating a broad range of devices requiring software developers to design software that can cope with this fragmented and diverse world. Thankfully, the Android software development framework is designed to deal with a hardware eco-system that is diverse and continuously evolving. One specific approach the framework uses is to allow developers to tag an application with the hardware/software features required in a target phone.

Android platform is still evolving

The platform is still rapidly evolving with a new major release posted nearly every 6 months. In a way, Android is just like Windows with a range of different versions in active use. Currently most mobile devices run either version 2.1 or 2.2 release of the Android platform (fortnightly reports on usage are posted here by Google ). Newer models often use the 2.3 release, while the newly announced Android tablets run the 3.x release which is designed for the larger screen real-estate that is available on those devices.

Applications are forward-compatible (i.e. If developed for 2.1, they will run fine on 2.2 and 2.3), but are not backward compatible. Although, the platform is open source and freely available, most users do not have sufficient technical knowledge, or the desire to update the operating environment — just like most of us not updating the firmware in the fridge. Sadly, to ensure the application is available to a sufficiently large market, developers have to currently target Android 2.2 release. In this masterclass series, release 2.2 will be the assumed primary target.

Android and Java

Android is a bi-lingual platform. Developers have the choice of using either Java or C/C++ as their primary programming language of choice. However, in practice most of the applications are currently built in Java using the Eclipse IDE. The tooling, documentation, and online community support is also built for programming in Java.

Android developers made two critical changes to the Java environment to ensure that it works well on a mobile device. First, they opted to use the Dalvik virtual machine with optimisations for a mobile device rather than the Oracle/Sun Java Virtual Machine technology. Secondly, they rebuilt the standard library and have intentionally omitted many parts that are found in the Oracle/Sun Java. In a nutshell, they eliminated much of the bloat and provided a library/framework that runs smoothly even on an older generation mobile device — especially, for the UI and graphics library.

Setting up the Android Environment

An Android programming environment requires installing a set of tools all of which are available for Windows, OSX and Linux.

They include

• Oracle/Sun Java 6 Software Development Kit (SDK)
• Eclipse IDE
• Eclipse Android Plug-in

The Android SDK provides an emulator to help developers deploy and test their applications without the need for an external hardware device. The emulator is similar to VM-Ware virtualisation solution, in that it emulates the complete mobile device hardware in a host operating system and literally boots-up the Android operating system on the emulated device. The advantage of an emulator is that developers can test an application for a specific operating system release and screen size. For example, we can create and test for an old release like 1.6 with a 3in screen. The downside of an emulator is that it does not have sensors that a physical phone has and the development tools do not offer a sufficiently useful simulation of these sensors.

Do I need an Android device to get started?

To get started, the emulator is sufficient and for the scope of this masterclass series it will be adequate. However, there are a number of aspects unique to a mobile experience that can only be tested on a real device. Consider a simple question that will illustrate such an experience: “Are the buttons and labels appropriately sized and placed for use while walking?” 

The only way to properly answer this question is to test with a physical device. There are other issues such as occlusion (where the hand may be covering some part of the screen that is needed to complete a task) that are also hard to test on an emulator. The rest of the masterclass covers the process of installing the tools after which we will create the simple Hello World application.

Installing the Java development kit (JDK)

The JDK provides all the tools needed to develop and run Java programs. Download the JDK here (Alternatively, search for 'JDK' and pick the first link). We only need to download the vanilla JDK without any bundles (see highlighted sections in Figure 2 and Figure 3 below). If you are running OSX, Java is installed as part of the operating system. Run the installer once you have downloaded the appropriate package.

Figure 2: The links that you need to download are highlighted.

Figure 3: Windows JDK versions are highlighted, select Windows x86 if you are not sure.

Installing Eclipse IDE

Step 1: Navigate to eclipse.org and select the Downloads link.

Figure 4: Figure highlighting the Eclipse Download link.

Step 2: There are a number of different versions of Eclipse, download ‘Eclipse IDE for Java Developers’ (see image below). Eclipse is shipped as a zip file. Unzip the file, and move the “eclipse” directory into a location where you store your programs (e.g. C:\Program Files). In the Eclipse directory there is an executable file (eclipse.exe), create a shortcut on your desktop or other appropriate location to this file. Eclipse does not use the registry and will initialise when you run it for the first time.

Figure 5: Download the IDE for Java Developers (as highlighted in the figure)

Step 3: Launch Eclipse via shortcut or directly by running eclipse.exe to verify the installation. The initial launch screen will show a welcome message (see Figure 6). Click on the curved arrow icon (centre right) to move into the project view.

Figure 6: The initial launch screen of Eclipse

Eclipse IDE uses views to organise information about projects and files that are currently open. (see Figure 7 for the views you will see on first launch). You can customise and configure the views extensively. For our development task, we do not need the Task List view, and hence that can be closed. The Package Explorer view will show the various projects as we work through them — this is where we can navigate the files within one or more projects. The Outline view shows the methods and fields in a class or other open entities — this view is helpful to quickly navigate the currently open file. In the bottom, we have other views that are helpful to identify any errors, and also to see messages.

Feel free to explore the files in the Hello Android project. Android development is built around a set of simple conventions to help organise a project and increase productivity. We will explore these conventions and build a slightly more interesting application in the next part of the masterclass series.

NEXT: Building a simple Android app