Android is a software stack for mobile devices that includes an operating system, middleware, and key applications. Android is a software platform and operating system for mobile devices based on the Linux operating system and developed by Google and the Open Handset Alliance. It allows developers to write managed code in a Java-like language that utilizes Google-developed Java libraries but does not support programs developed in native code.
The unveiling of the Android platform on 5 November 2007 was announced with the founding of the Open Handset Alliance, a consortium of 34 hardware, software and telecom companies devoted to advancing open standards for mobile devices. When released in 2008, most of the Android platform will be made available under the Apache free-software and open-source license.
Open Android allows accessing core mobile device functionality through standard API calls. Android does not differentiate between the phone’s basic and third-party applications. Even the dialer or home screen can be replaced. SDK contains what needs to build and run Android applications, including a true device emulator and advanced debugging tools.
THE BIRTH OF ANDROID
In July 2005, Google acquired Android Inc., a small startup company based in Palo Alto, CA. Android’s co-founders who went to work at Google included Andy Rubin (co-founder of Danger), Rich Miner (co-founder of Wildfire Communications, Inc), Nick Sears (once VP at T-Mobile), and Chris White (one of the first engineers at WebTV). At the time, little was known about the functions of Android Inc. other than they made software for mobile phones.
1. Open Handset Alliance Founded
On 5 November 2007, the Open Handset Alliance, a consortium of several companies which include Google, HTC, Intel, Motorola, Qualcomm, T-Mobile, Sprint Nextel and NVIDIA, was unveiled with the goal to develop open standards for mobile devices. Along with the formation of the Open Handset Alliance, the OHA also unveiled their first product, Android, an open source mobile device platform based on the Linux operating system.
Google has unveiled at least three prototypes for Android, at the Mobile World Congress on February 12, 2008. One prototype at the ARM booth displayed several basic Google
Features of Android OS:
1.Application framework enabling reuse and replacement of components
2.Dalvik virtual machine optimized for mobile devices
3.Integrated browser based on the open-source WebKit engine
4.Optimized graphics powered by a custom 2D graphics library; 3D graphics based on the OpenGL ES 1.0 specification (hardware acceleration optional)
5.SQLite for structured data storage.
6.Media support for common audio, video, and still image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)
7.GSM Telephony (hardware dependent)
8.Bluetooth, EDGE, 3G, and WiFi (hardware dependent)
The following diagram shows the major components of Android
Developers have full access to the same framework APIs used by the core applications. The application architecture is designed to simplify the reuse of components; any application can publish its capabilities and any other application may then make use of those capabilities (subject to security constraints enforced by the framework). This same mechanism allows components to be replaced by the user.
Underlying all applications is a set of services and systems, including:
- A rich and extensible set of Views that can be used to build an application, including lists, grids, text boxes, buttons, and even an embeddable web browser
- Content Providers that enable applications to access data from other applications (such as Contacts), or to share their own data
- A Resource Manager, providing access to non-code resources such as localized strings, graphics, and lat files
- A Notification Manager that enables all applications to display custom alerts in the status bar An Activity Manager that manages the lifecycle of applications and provides a common navigation back stack.
Android includes a set of C/C++ libraries used by various components of the Android system. These capabilities are exposed to developers through the Android application framework. Some of the core libraries are listed below:
- System C library – a BSD-derived implementation of the standard C system library (lib C), tuned for embedded Linux-based devices
- Media Libraries – based on PacketVideo’s Open CORE; the libraries support playback and recording of many popular audio and video formats, as well as static image files, including MPEG4, H.264, MP3, AAC, AMR, JPG, and PNG
- Surface Manager – manages access to the display subsystem and seamlessly composites 2D and 3D graphic layers from multiple applications
- LibWebCore – a modern web browser engine which powers both the Android browser and an embeddable web view
- SGL – the underlying 2D graphics engine
- 3D libraries – an implementation based on OpenGL ES 1.0 APIs; the libraries use either hardware 3D acceleration (where available) or the included, highly optimized 3D software rasterizer
- Free Type – bitmap and vector font rendering
- SQLite – a powerful and lightweight relational database engine available to all applications.
It is possible to have multiple instances of Dalvik virtual machine running on the single device at the same time. The Core libraries are written in Java language and contains collection classes, the utilities, IO and other tools.
that provides most of the functionality available in the core libraries of the Java programming language. Every Android application runs in its own process, with its own instance of the Dalvik virtual machine. Dalvik has been written so that a device can run multiple VMs efficiently. The Dalvik VM executes files in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint. The VM is register-based and runs classes compiled by a Java language compiler that has been transformed into the .dex format by the included “dx” tool. The Dalvik VM relies on the Linux kernel for underlying functionality such as threading and low-level memory management.
At the same level, there is Android Runtime, where the main component Dalvik Virtual Machine is located. It was designed specifically for Android running in the limited environment, where the limited battery, CPU, memory and data storage are the main issues. Android gives an integrated tool dx, which converts generated bytecode from .jar to .dex file after this bytecode becomes much more efficient to run on the small processors.
Android Architecture is based on Linux 2.6 kernel. It helps to manage security, memory management, process management, network stack and other important issues. Therefore, the user should bring Linux into his mobile device as the main operating system and install all the drivers required in order to run it. Android provides the support for the Qualcomm MSM7K chipset family. For instance, the current kernel tree supports Qualcomm MSM 7200A chipsets, but in the second half of 2008 we should see mobile devices with stable version Qualcomm MSM 7200, which includes major features:
1. WCDMA/HSUPA and EGPRS network support
2. Bluetooth 1.2 and Wi-Fi support
3. Digital audio support for mp3 and other formats
4. Support for Linux and other third-party operating systems
5. Java hardware acceleration and support for Java applications
6. Qcamera up to 6.0 megapixels
7. gpsOne solution for GPS
The Dalvik Virtual Machine:
The Dalvik virtual machine is an interpreter only machine optimized for use on low powered, low memory devices like phones. Notably, Dalvik does not make use of just in time (JIT) Compilation to improve the performance of an application at runtime. Furthermore, Dalvik is not a Java virtual machine. This is because Dalvik is unable to read Java bytecode34, instead, it uses its own bytecode format called dex. Google claims this format allows battery power to be better-conserved at all different stages of execution of an application. This means that standard Java SE applications and libraries cannot be used directly on the Android Dalvik virtual machine.
Dalvik, however, stands at the center of the Android value proposition. Its low electrical power consumption, rich libraries, and unified, non-fragmented application programming interfaces make it stand out, or so Google hopes, over the fragmented ecosystem that is Java ME35 today.
Furthermore, since Dalvik uses the Java programming language but not the Java execution environment (JVM), Google is free to develop Android without the need to license or obtain certification from Sun Microsystems Inc, the legal owner of the Java trademark and brands.
The lifecycle of Android Application:
In most cases, every Android application runs in its own Linux process. This process is created for the application when some of its code needs to be run and will remain running until it is no longer needed and the system needs to reclaim its memory for use by other applications.
An important and unusual feature of Android is that an application process’s lifetime is not directly controlled by the application itself. Instead, it is determined by the system through a combination of the parts of the application that the system knows are running, how important these things are to the user, and how much overall memory is available in the system.
It is important that application developers understand how different application components (in particular Activity, Service, and IntentReceiver) impact the lifetime of the application’s process. Not using these components correctly can result in the system killing the application’s process while it is doing important work.
A common example of a process life-cycle bug is an IntentReceiver that starts a thread when it receives an Intent in its onReceiveIntent() method, and then returns from the function. Once it returns, the system considers that IntentReceiver to be no longer active, and thus its hosting process no longer needed (unless other application components are active in it). Thus, it may kill the process at any time to reclaim memory, terminating the spawned thread that is running in it. The solution to this problem is to start a Service from the IntentReceiver, so the system knows that there is still active work being done in the process.
To determine which processes should be killed when low on memory, Android places them into an “importance hierarchy” based on the components running in them and the state of those components. These are, in order of importance:
- A foreground process is one holding an Activity at the top of the screen that the user is interacting with (its onResume () method has been called) or an IntentReceiver that is currently running (its onReceiveIntent () method is executing). There will only ever be a few such processes in the system, and these will only be killed as a last resort if memory is so low that not even these processes can continue to run. Generally, at this point, the device has reached a memory paging state, so this action is required in order to keep the user interface responsive.
- A visible process is one holding an Activity that is visible to the user on-screen but not in the foreground (its onPause() method has been called). This may occur, for example, if the foreground activity has been displayed with a dialog appearance that allows the previous activity to be seen behind it. Such a process is considered extremely important and will not be killed unless doing so is required to keep all foreground processes running.
- A service process is one holding a Service that has been started with the startService() method. Though these processes are not directly visible to the user, they are generally doing things that the user cares about (such as background mp3 playback or background network data upload or download), so the system will always keep such processes running unless there is not enough memory to retain all foreground and visible process.
- A background process is one holding an Activity that is not currently visible to the user (its onStop() method has been called). These processes have no direct impact on the user experience. Provided they implement their activity life cycle correctly (see Activity for more details), the system can kill such processes at any time to reclaim memory for one of the three previous processes types. Usually, there are many of these processes running, so they are kept in an LRU list to ensure the process that was most recently seen by the user is the last to be killed when running low on memory.
- An empty process is one that doesn’t hold any active application components. The only reason to keep such a process around is as a cache to improve startup time the next time a component of its application needs to run. As such, the system will often kill these processes in order to balance overall system resources between these empty cached processes and the underlying kernel caches.
When deciding how to classify a process, the system picks the most important level of all the components currently active in the process.
Security and Permissions in Android:
Android is a multi-process system, where each application (and parts of the system) runs in its own process. Most security between applications and the system is enforced at the process level through standard Linux facilities, such as user and group IDs that are assigned to applications. Additional finer-grained security features are provided through a “permission” mechanism that enforces restrictions on the specific operations that a particular process can perform.
Android mobile phone platform is going to be more secure than Apples iPhone or any other device in the long run. There are several solutions nowadays to protect Google phone from various attacks. One of them is security vendor McAfee, a member of Linux Mobile (LiMo) Foundation. This foundation joins particular companies to develop an open mobile-device software platform. Many of the companies listed in the LiMo Foundation have also become members of the Open Handset Alliance (OHA).
As a result, Linux secure coding practice should successfully be built into the Android development process. However, the open platform has its own disadvantages, such as source code vulnerability for black-hat hackers. In parallel with great opportunities for mobile application developers, there is an expectation for exploitation and harm. Stealthy Trojans hidden in animated images, particular viruses passed from friend to friend, used for spying and identity theft, all these threats will be active for a long run.
Another solution for such attacks is SMobile Systems mobile package. Security Shield an integrated application that includes anti-virus, anti-spam, firewall and other mobile protection is up and ready to run on the Android operating system. Currently, the main problem is availability for viruses to pose as an application and do things like dial phone numbers, send text messages or multimedia messages or make connections to the Internet during normal device use. It is possible for somebody to use the GPS feature to track a person’s location without their knowledge. Hence SMobile Systems is ready to notify and block these secure alerts. But the truth is that it is not possible to secure mobile device or personal computer completely, as it connects to the internet. And neither the Android phone nor other devices will prove to be the exception.
The Android SDK includes a variety of custom tools that help develop mobile applications on the Android platform. The most important of these are the Android Emulator and the Android Development Tools plugin for Eclipse, but the SDK also includes a variety of other tools for debugging, packaging, and installing r applications on the emulator.
A virtual mobile device that runs on computer use the emulator to design, debug, and test r applications in an actual Android run-time environment.
Android Development Tools Plugin for the Eclipse IDE
The ADT plugin adds powerful extensions to the Eclipse integrated environment, making creating and debugging r Android applications easier and faster. If use Eclipse, the ADT plugin gives an incredible boost in developing Android applications:
- It gives access to other Android development tools from inside the Eclipse IDE. For example, ADT lets access the many capabilities of the DDMS tool taking screenshots, managing port-forwarding, setting breakpoints, and viewing thread and process information directly from Eclipse.
- It provides a New Project Wizard, which helps quickly create and set up all of the basic files need for a new Android application.
- It automates and simplifies the process of building r Android application.
- It provides an Android code editor that helps write valid XML for r Android manifest and resource files.
Dalvik Debug Monitor Service (DDMS)
Integrated with Dalvik, the Android platform’s custom VM, this tool lets manage processes on an emulator or device and assists in debugging. can use it to kill processes, select a specific process to debug, generate trace data, view heap and thread information, take screenshots of the emulator or device, and more.
Android Debug Bridge (ADB)
The ADB tool lets install application’s .apk files on an emulator or device and access the emulator or device from a command line. can also use it to link a standard debugger to application code running on an Android emulator or device.
Android is a truly open, free development platform based on Linux and open source. Handset makers can use and customize the platform without paying a royalty.
A component-based architecture inspired by Internet mash-ups. Parts of one application can be used in another in ways not originally envisioned by the developer. Can even replace built-in components with own improved versions. This will unleash a new round of creativity in the mobile space.
- Android is open to all: industry, developers, and users.
- Participating in many of the successful open source projects.
- Aims to be as easy to build for as the web.
- Google Android is stepping into the next level of Mobile Internet.