Inside Google's mobile future

Google's foray into the handheld OS realm follows a path well trodden by others, but will it succeed?

Android is Google's foray into the handheld OS realm. It follows a path trodden by -- among others -- Symbian's Quartz, the SavaJe operating system, and J2ME. In fact, one of Android's stated goals is to overcome some of J2ME's shortcomings. Whether or not Android succeeds, either at that specific goal, or in general, remains to be seen.

This article addresses a specific question: What is it like to work with the Android SDK? And to a lesser extent: What is under the Android hood? As these questions are answered, bear in mind that the version of the Android SDK I used was not in final form. Some of the problems described may have -- in fact, I hope will have -- been corrected by the time you read this. In addition, while Android development is supported on Linux, Mac OS X, and Windows, I did all my testing on Windows systems.

Inside an Android

Peel away Android's carapace, dig down to its marrow, and you'll find a Linux kernel. Libraries are a layer above, a variety of frameworks above that, and a final layer of applications sits on the top. The library layer is home to code for entities such as media processors for playback and recording of audio and video, the core of the Web browser, font rendering, and the SQLite relational database engine. The Android runtime also lives in the library layer.

Above the libraries reside frameworks, which are sets of reusable services and common components available to applications. For example, one sort of framework is a content provider, which is any service that handles the storage and retrieval of data. The application interface into the SQLite engine is a specific instance of a content provider.

Applications run at the top of the OS stack. Android will ship (assuming that it eventually does ship) with a set of core applications, including an e-mail client, a calendar, a Web browser, and more. And, of course, it is toward this topmost layer that all of the faculties of the Android SDK are directed.

When a developer writes an Android application, that developer codes in Java. The Java source is compiled to Java bytecodes, but -- to execute the application on Android -- the developer must execute a tool called dx. This tool converts Java bytecode to what is referred to as dex bytecodes. "Dex" is short for "Dalvik executable," Dalvik being the virtual machine that actually executes Android applications.

From a developer's perspective, Dalvik looks like a Java Virtual Machine, but strictly speaking, Dalvik is not a JVM. As stated above, Dalvik executes dex bytecode, not Java bytecode. And there are differences in the structure of Dalvik class files as compared to Java class files. Nevertheless, for all intents and purposes, building an Android application is really an exercise in building a peculiar sort of Java application.

Join the newsletter!

Or

Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.
Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Rick Grehan

InfoWorld
Show Comments

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Tom Pope

Dynabook Portégé X30L-G

Ultimately this laptop has achieved everything I would hope for in a laptop for work, while fitting that into a form factor and weight that is remarkable.

Tom Sellers

MSI P65

This smart laptop was enjoyable to use and great to work on – creating content was super simple.

Lolita Wang

MSI GT76

It really doesn’t get more “gaming laptop” than this.

Jack Jeffries

MSI GS75

As the Maserati or BMW of laptops, it would fit perfectly in the hands of a professional needing firepower under the hood, sophistication and class on the surface, and gaming prowess (sports mode if you will) in between.

Taylor Carr

MSI PS63

The MSI PS63 is an amazing laptop and I would definitely consider buying one in the future.

Christopher Low

Brother RJ-4230B

This small mobile printer is exactly what I need for invoicing and other jobs such as sending fellow tradesman details or step-by-step instructions that I can easily print off from my phone or the Web.

Featured Content

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?