Android is based on linux for the following reasons :

1. SECURITY

2. PORTABILITY

3. NETWORKING

Some of the elements of Android application architecture are:

• Firstly, Services for performing background functionalities.
• Secon, Intent for performing the interconnection between activities and the data passing mechanism.
• Thirdly, Resource Externalization covers strings and graphics.
• Then, Notification which includes light, sound, icon, notification, dialog box, and toast.
• Lastly, Content Providers help in sharing the data between applications.

An Activity refers to the screen representation of an application in Android. This acts as the starting point for the user’s interaction. However, every activity consists of a layout file where you can store your UI. Further, an application can have various activities like a Facebook start page where you enter your email/phone and password for logging in can be considered as an activity. The methods which almost all subclasses of Activity will implement:

• Firstly, onCreate(Bundle). This method performs initialization. Here you will callsetContentView(int) with a layout resource that specifies your UI.
• Secondly, onPause(). This method interacts with the user whenever it leaves the activity. So any modifications made by the user should be carried out by the ContentProvider that holds the data.

By introducing Android, Google has changed the lives of everyone by improving the mobile experience. Some of the major features include:

• Firstly, it provides customizable operating System
• There are a variety of apps that can be developed.
• Then, it lowers down overall complexity
• Also, it has the support of messaging services, web browser, storage(SQLite), connectivity, media, and more.

An Intent can be defined as an “intention” for doing an action. This is basically a messaging object you can use for requesting action from another app component. However, methods are used for delivering intents to different components. They are:

• Firstly, for starting an activity, context.startActivity().
• Then, for starting a service, context.startService().
• Lastly, for delivering a broadcast, context.sendBroadcast().

There are two types of intent:

1. Implicit Intent This can be stated as to when the target component is not specified in the intent and the android system has to examine the registered components depending on the intent data.

2. Explicit Intent This can be stated as to when an application-specific the target component directly in the intent.

• A file refers to a block of arbitrary information or resources for storing information.
• A class can be considered as a compiled form of the .Java file which Android uses for producing an executable apk.
• Lastly, activity refers to an equivalent of a Frame/Window in GUI toolkits. This cannot be considered as a file or a file type but just a class that can be expanded in Android for loading UI elements on view.

The Google Android SDK refers to a toolset that provides a developer the API libraries and tools needed for building, testing, and debugging apps for Android in Windows, Mac, or Linux. However, some of the tools placed in Android SDK are:

• Firstly, Android Emulator
• Secondly, Dalvik Debug Monitoring Services (DDMS)
• Thirdly, the Android Asset Packaging tool (AAPT)
• Lastly, the Android debug bridge (ADB)

Android Framework is an important part of Android Architecture. This is a set of APIs that provides developers access to write apps. This includes components like:

• Firstly, Services for performing background functionalities. This conducts log-running operations.
• Secondly, Intent for performing the interconnection between activities and the data passing mechanism. In this, the objects take actions from app components inside the program.
• Thirdly, Activities include components used for providing users with screens on which they can interact with objects and perform actions.
• Lastly, Content Providers help in sharing the data between applications. This enables users to access data inside an application like audio, video, or images.

DDMS stands for Dalvik Debug Monitor Server which is a debugging tool in the Android platform. The features include:

• Port forwarding services.
• Thread and heap information.
• Logcat.
• Screen capture on the device.
• Network traffic tracking.
• Incoming calls and SMS spoofing.
• Location data spoofing.

There are three categories of sensors in Android devices.

• Firstly, Position Sensor - This is used for measuring the physical position of the Android device. This contains orientation sensors and magnetometers.
• Secondly, Motion Sensors - These sensors contain gravity, rotational activity, and acceleration sensors which help in measuring the rotation of the device or the acceleration, etc.
• Lastly, Environmental Sensor - This contains sensors that help in measuring temperature, humidity, pressure, and other environmental factors.

The AndroidManifest.xml file consists of information with reference to the application that the Android system must know before the codes can be executed. Further, this file is essential in every Android application and is declared in the root directory. However, it performs various tasks like:

• Firstly, providing a unique name to the java package.
• Secondly, explaining various elements of the application such as activity, services, etc.
• Lastly, specifying the classes which will implement these elements.

1. App This explains the fundamental characteristics of the app and defines each of its components.

2. Java This consists of the .java source files for your project. By default, it contains a MainActivity.java source file. Under this, you create all the activities which have .java extensions and all the code behind the application. MainActivity.java is the actual file that gets transformed to a Dalvik executable and runs your app.

3. Res This is referred to as a directory for files that define your app’s user interface. You can add TextView, buttons, etc for building the GUI and using its various attributes like android:layout_width, android:layout_height, etc which are used to set its width and height.

4. Scripts This can be considered as an auto-generated file that consists of compileSdkVersion, buildToolsVersion, applicationId, minSdkVersion, targetSdkVersion, versionCode, and versionName

The measures can be taken to avoid ANR:

• Firstly, an application should execute lengthy database or networking operations in different threads to avoid ANR.
• Secondly, for background task-intensive applications, you can minimize the pressure from the UI thread by using the IntentService.

You can perform techniques like:

1. Compatibility Check -  It is difficult to test an application for all kinds of devices and operating systems. There might be a possibility that an application is not compatible with your OS.

2. Memory Management - Some apps execute perfectly on one mobile device but might crash on other devices. Processing power, memory management, and CPU speed are considered to be an issue.

• If there is a limited amount of memory space on mobile devices, you can free up memory space for the application for functioning properly.
• If still an application is frequently crashing, then can delete the application’s data, which will clear its cache memory and allow some free space on your device for boosting the application’s performance.

1. Standard This launch mode creates an activity’s new instance in the task from which it originated. This can create several instances for the same activity.

2. SingleTop This launch mode is the same as the Standard launch mode except if there exists an activity’s previous instance on the top of the stack, then a new instance will not be built. However, the intent will be sent to the activity’s existing instance.

3. SingleTask This launch mode will build a new task and push a new instance to the task as the root.

4. SingleInstance This launch mode is the same as the SingleTask launch mode. But the system doesn’t support launching any new activities in the same task.

While developing applications commonly it is required for transferring data from one activity to another. This data needs to be added to a corresponding intent object. Some additional actions are needed for making the data suitable for transfer. For this, the object should be either serializable or parcelable.

• Firstly, Serializable refers to a standard Java interface in which you simply mark a class Serializable by implementing the interface and java will automatically serialize it. In this, there is the use of reflection and many additional objects are created. This leads to many garbage collections and poor performance.
• Secondly, Parcelable is an Android-specific interface in which you implement the serialization yourself. This does not use reflection during this process and hence no garbage is created.
• Further, this is more efficient than Serializable since it gets around some problems with the default Java serialization scheme. And, it is faster because it is optimized for usage on the development of Android, and shows the best results.