Android

Android is an open source operating system for mobile and other electronic gadgets including some laptop.
The Android operating system software stack consists of Java applications running on a Java based object oriented application framework on top of Java core libraries running on a Dalvik virtual machine featuring JIT compilation.

Basics of Android:
1) Open source OS 
2) Uses Linux kernel
3) Optimized for limited-resource environment
4) Apps typically written in Java
5) Apps run on the Dalvik Virtual Machine
6) Not a JVM, but works similarly from developer’s point of view
7) Usually one app per DVM
8) Each DVM runs under Linux as a separate user
9)App permissions set at install time
10) Possible to use C or C++ compiled to machine code, but still runs on VM. 

Standard development environment is Eclipse + Android Development Tools plugin + Android SDK or Android Studio, which is new IDE from Google for developer and Development requires either an Android OS device or an emulator Emulator has limitations: Performance is poor Camera, etc., simulated using your computer’s hardware No real phone calls or texts GPS data, battery readings, etc. must be simulated Real device is affected by specific hardware and software configuration.

android installation

Android Studio can be downloaded from here and to set up Android on windows machine, follow the steps.

1. Click on .exe file to start setup.
2. Follow steps as mentioned on the setup screens.3. Set Environment variables for JAVA:- Select Start menu > Computer > System Properties > Advanced System Properties. Then open Advanced tab > Environment Variables and add a new system variable JAVA_HOME that points to your JDK folder, for example C:\Program Files\Java\jdk1.2

creating first android program/app

Steps to create your first Android Program/App:-

1) Application Name: application name is nothing but the name of your app. This name is visible on the screen when the app is installed. The application name is also shown in Google Play Store when you upload your application.

2) Project Name: Project name is the name of your project that gets created in eclipse. You can give any name to your project. Package Name: This is very important. Package name is used to uniquely identify your application on Play Store. You should follow the java package convention for the package name . The package name is not shown to the user but should not change ever. A good approach to choose package name is to use the reverse of your company domain name. For example :- com.mitindia

3) Min Required SDK: As you might know, Android started with version 1.5 and its current version is 5.0 These numbers represents different flavors of Android, like 2.3 is termed Gingerbread, 4.1 as Ice Cream Sandwich etc. These names are used for marketing the OS, while version numbers are of interest to developers. Min Required SDK field gives you the flexibility to decide which version of android at minimum you want to support. For example, if you create an application for android 2.3 it will work on android 4.4. In general, it is advisable to have minimum support of 2.3.3 API Version 9.

4) Target SDK: This setting tells android that even though your app will be able to run on its previous android version, but it is explicitly tested with version specified here in this field.

5) Compile With: This option gives lets you choose the version of SDK you want to compile with. Typically,the highest version which is available in your ADT should be chosen here. This will compile your app with the latest code and optimizations.

6) Theme: If you are creating apps for version 4.X and above you can have an application wide theme. These themes are nothing but some pre defined color schemes, which you can use to improve your application's User Interface.

SUM of 2 Numbers programs using Android 

for more detail you can browse here