Architecture of Android
Architecture of Android
In order to understand how Android works, take a look at below Figure , which shows the various layers that make up the Android operating system (OS).
The Android OS is roughly divided into five sections in four main layers:
➤➤ Linux kernel — This is the kernel on which Android is based. This layer contains all the lowlevel device drivers for the various hardware components of an Android device.
➤➤ Libraries — These contain all the code that provides the main features of an Android OS. For example, the SQLite library provides database support so that an application can use it for data storage. The WebKit library provides functionalities for web browsing.
➤➤ Applications — At this top layer, you will find applications that ship with the Android device (such as Phone, Contacts, Browser, etc.), as well as applications that you download and install from the Android Market. Any applications that you write are located at this layer.
Android Devices in the Market
Android devices come in all shapes and sizes. As of late November 2010, the Android OS can be seen powering the following types of devices:
➤➤ Smartphones
➤➤ Tablets
➤➤ E-reader devices
➤➤ Netbooks
➤➤ MP4 players
➤➤ Internet TVs
Chances are good that you own at least one of the preceding devices. Above Figure shows (clockwise) the Samsung Galaxy S, the HTC Desire HD, and the LG Optimus One smartphones.
Another popular category of devices that manufacturers are rushing out is the tablet. Tablet sizes typically start at seven inches, measured diagonally. Figure 1-3 shows the
Samsung Galaxy Tab and the Dell Streak, which is a fiveinch phone tablet.
In addition to these popular mobile devices, Android is also slowly finding its way into your living room. People of Lava, a Swedish company, has developed an Android-based TV, call the Scandinavia Android TV (see below Figure).
Google has also ventured into a proprietary smart TV platform based on Android and co-developed with companies such as Intel, Sony, and Logitech. Figure 1-6 shows Sony’s Google TV.
➤➤ Smartphones
➤➤ Tablets
➤➤ E-reader devices
➤➤ Netbooks
➤➤ MP4 players
➤➤ Internet TVs
Chances are good that you own at least one of the preceding devices. Above Figure shows (clockwise) the Samsung Galaxy S, the HTC Desire HD, and the LG Optimus One smartphones.
Another popular category of devices that manufacturers are rushing out is the tablet. Tablet sizes typically start at seven inches, measured diagonally. Figure 1-3 shows the
Samsung Galaxy Tab and the Dell Streak, which is a fiveinch phone tablet.
In addition to these popular mobile devices, Android is also slowly finding its way into your living room. People of Lava, a Swedish company, has developed an Android-based TV, call the Scandinavia Android TV (see below Figure).
Google has also ventured into a proprietary smart TV platform based on Android and co-developed with companies such as Intel, Sony, and Logitech. Figure 1-6 shows Sony’s Google TV.
The Android market
As mentioned earlier, one of the main factors determining the success of a smartphone platform is the applications that support it. It is clear from the success of the iPhone that applications play a very vital role in determining whether a new platform swims or sinks. In addition, making these applications accessible to the general user is extremely important. As such, in August 2008, Google announced the Android Market, an online application store for Android devices, and made it available to users in October 2008. Using the Market application that is preinstalled on their Android device, users can simply download third-party applications directly onto their devices. Both paid and free applications are supported on the Android Market, though paid applications are available only to users in certain countries due to legal issues.
Similarly, in some countries, users can buy paid applications from the Android Market, but developers cannot sell in that country. As an example, at the time of writing, users in India can buy apps from the Android Market, but developers in India cannot sell apps on the Android Market. The reverse may also be true; for example, users in South Korea cannot buy apps, but developers in South Korea can sell apps on the Android Market.
Obtaining the required tools Now that you know what Android is and its feature set, you are probably anxious to get your hands dirty and start writing some applications! Before you write your fi rst app, however, you need to download the required tools and SDKs.
For Android development, you can use a Mac, a Windows PC, or a Linux machine. All the tools needed are free and can be downloaded from the Web. Most of the examples provided in this book should work fine with the Android emulator, with the exception of a few examples that require access to the hardware.
Let's using a Windows 7 computer to demonstrate all the code samples. If you are using a Mac or Linux computer, the screenshots should look similar; some minor differences may be present, but you should be able to follow along without problems.
As mentioned earlier, one of the main factors determining the success of a smartphone platform is the applications that support it. It is clear from the success of the iPhone that applications play a very vital role in determining whether a new platform swims or sinks. In addition, making these applications accessible to the general user is extremely important. As such, in August 2008, Google announced the Android Market, an online application store for Android devices, and made it available to users in October 2008. Using the Market application that is preinstalled on their Android device, users can simply download third-party applications directly onto their devices. Both paid and free applications are supported on the Android Market, though paid applications are available only to users in certain countries due to legal issues.
Similarly, in some countries, users can buy paid applications from the Android Market, but developers cannot sell in that country. As an example, at the time of writing, users in India can buy apps from the Android Market, but developers in India cannot sell apps on the Android Market. The reverse may also be true; for example, users in South Korea cannot buy apps, but developers in South Korea can sell apps on the Android Market.
Obtaining the required tools Now that you know what Android is and its feature set, you are probably anxious to get your hands dirty and start writing some applications! Before you write your fi rst app, however, you need to download the required tools and SDKs.
For Android development, you can use a Mac, a Windows PC, or a Linux machine. All the tools needed are free and can be downloaded from the Web. Most of the examples provided in this book should work fine with the Android emulator, with the exception of a few examples that require access to the hardware.
Let's using a Windows 7 computer to demonstrate all the code samples. If you are using a Mac or Linux computer, the screenshots should look similar; some minor differences may be present, but you should be able to follow along without problems.
