For those who are interested in using Java in android applications and who are currently into developing applications written in C# using .net framework then I recommend the following points that could give you an idea on how to start:

.Net Developers Get Started with Android

1. First of all, I suggest that you use Android Studio as the Integrated Development Environment(IDE). It is light and simple to use. The environment is pretty much the same as that of Visual Studio. It is like mobile IDE version of the visual studio where you can find the following cool features: 

   1.1.  Project wizard creation. This feature will help you in naming your project, choosing android devices. It will also help in adding activity from different templates and you’re done.  Codes and layout page are easily generated. After that, project is ready to run.

   1.2.  Drag and drop. Widgets and layouts can be dragged and dropped on the page, then the codes will be generated automatically.

   1.3.  Code assistant. If you are familiar with ReShaper then this what I exactly mean. Yes, it’s like as if you have a free tool. This is what I like the most, it will really speed up your coding. 

   You can found a complete reference guide from downloading the Android Studio, its features and other using this link. 

2. Next you may opt to use online materials. Once your development environment is set up then you can start creating application. A very good tutorial is uploaded in youtube.  You can check it out using the following link:

     

   The link is a series of tutorials that covers most of the fundamental concepts and shows you how to create a mobile application from creating the project up to saving data into a database. 

   An effective way to learn the tutorial is to follow the steps while watching it. And if you encounter some doubts or if there are some concepts that you don’t understand then go back to previous tutorial and replay the video and review it. On my case, I started following the codes using the “Android App Development Tutorial - 36 - Create a Note Taking App” down to the last tutorial. 

3. You need also to review. Review Java. It is true that if you are a C# developer you will find many of the syntax in C# similar in Java but I think it is also important to be familiar with the differences of the two languages. A good reference that I came across with is this link. 
4. Finally, note some fundamental concepts. One of the time consuming activity in the mobile application is the development of the user interface. I suggest that you pay attention on the fundamental layout designs such as LinearLayout, RelativeLayout and GridLayout. Know when is the best time to use either of these or when to use both.
   
   Another useful approach in displaying data in view is by using Listview or Gridview. The basic concept is data binding. First you must create the source of data and the associated layout. Next set this as source of data for listview or gridview. Hence, your knowledge in Asp.net listview and gridview are basically the same and an advantage on your part. 

Being a web developer and creating various web applications is very rewarding. However, expanding your horizon into the mobile application is not only rewarding but also fulfilling. So, what are you waiting for let the android studio begins.