Develop Reference

Is it possible to develop 2D games in Android Studio?

I have searched in the web and found very few material on this question. I've heard of Unity 3D and know that there are other tools. But I would like to know if it is possible to develop games in Android Studio? I'm learning Android development and Java, therefore don't want to jump into other language and platforms. However, if it is not efficient way then which one you would advice? Where to start?

Yes it's possible. You can make your own game by using game engine that freely available for Android.
You can use LibGDX. For the tutorial with Android Studio, you can read here.
Visit Sample 2D game with LibGDX

Yes of course it is possible. But there are some things you should know. Games made without a game engine are usually not as good as you might expect. You define the interaction of the objects in the game with each other with simple codes, but there are collider structures developed for this in game engines. In addition, while adding effects to the game is easy with the game engine, doing this without the game engine is more difficult and does not show a stable working performance.
here are some 2D game tutorials you can do without using a game engine
game-1
game-2

App in Android, porting in iOS

I have developed an app with Eclipse, a little stupid game.
If I wanted to port it in iOS, is there any hurting way to do it?
I mean, can I re-use xml code for GUI?
May I re-use my DB (I think so, it would be horrible if not).
If I learnt how to use libgdx or unity it would be compatible with both platforms?
Is there a good guide to understand one of them? I can't find any good guides online.

If you write your game in Unity or PhoneGap/Cordova, it would be compatible with both devices. I personally recommend Unity more because it's geared toward game development.

Android 2D Game advice

Hi there I want to design 2D games for android but I don't know where to start. I haven't developed any software for android platform either. Should I first learn programming on Android platform or find a book about 2D game development for Android and start from there?
Thanks for your help
Much appreciated..

Start with programming on the Android platform. Continue with a game framework, there are many. But almost all of them are some packages with classes added on top of the Android classes - it's not a brand new framework. So you must be familiar with the regular Android platform.
For the game framework, there are a few I know, pick one:
AndEngine
libGDX
cocos2d-android
Personally, I know AndEngine and it is really good in my opinion. There were some discussions about these 3 frameworks on SO, here are some of them:
Should I use cocos2D or andengine?
Andengine vs libgdx
What's the best free Android game engine? [closed]
Cocos2D OR libgdx for Android Game Developement (AndEngine is mentioned here too).

Port Andengine game to other platform?

I'm planning on writing a multiplayer game with Android as my primary focus as far as OS/platform, but I would like the ability to port the game to at least the web. I'm looking into Andengine as I'm just starting out with java and android and it seems the most noob friendly. The game shouldn't be too demanding as it will be a 2d turn based game with simple animations and chat.
So my main question - is it possible to port a Andengine game to the web?
If not what would you suggest?
I looked at libgdx, but I'm concerned that it might be a little to advanced for someone just starting out with java/android. Am I correct in my assumption?
Another idea I've been playing around with is writing the game in Flash and porting it to Android with Adobe Air - does anyone have any experience with this? Is it a bad idea? I kind of have my doubts of how well this will work, but if nobody can really talk me down from this idea, I might just go this route.
I've also considered writing the game in pygame as it seems easier but I don't like the idea of players having to download something like Pygame Subset for Android or Kivy to run the game. So basically if the other options are either too difficult or wont work on android then I'm probably just going to go with Andengine and consider rewriting it later for the web if people like it enough.

Moai SDK is an open source multi-platform framework for game developers.
One codes in lua - a dynamic programming language (that is easy to learn).
Apps made using Moai can be deployed to iOS, android and the chrome web store.
Moai could be an alternative.

Andengine makes a fine starting place. (I have made 3 projects with it now and I really like it). but it does not deploy to anything other than android. That is its strength and its weakness. As a strength, it is very easy to integrate android OS features and libraries with your project and has good performance. And as a weakness, well, it only runs on android.
Code-once publish anywhere platforms trade off development time for speed and size usually.
Some top competitors in that area are:
Ancsa Corona
AppMobi
PhoneGap
Unity3D
Adobe Flash(bonus of web distribution)
and others. (Moai SDK listed by #andrew, for example)
Each platform has had successful games launched with them. Find the one that suits you and your projects needs best. Do not forget to check for things you will want to integrate, such as using Facebook for mobile, or AdMob, or OpenFeint or other 3rd party services.
Good luck and enjoy you game making!

Just a side note, user do not need to download "Kivy" to run the game. As other toolkit, your application will provide Kivy as other libraries you'll use.

How to start developing a social multi-player game on android

I'd be very keen to know how to develop a social game on android which includes 2 or more than 2 players. Let's say chess..for example or scrabble.How to begin? Are there any online resources or tutorials available on this subject?

The best resource out there is Google's Android developer guide: http://developer.android.com/guide/topics/ui/index.html
This not only gives you an explanation for all the major classes of the android sdk, it also gives you tutorials into things such as reading from contacts (specifically the "content providers" section).
As for sockets, I don't think there is anything special with Android's Java implementation for that, you should just be able to find any Java socket tutorial and use that.

I think this is a good article on writing Android games: Getting Started in Android Game Development

Yup Skiller is a really cool social and multiplayer SDK. (you can download from here: http://www.skiller-games.com)
Also, you will need some kind of framework or a graphic environment, i recommend AndEngine which works for me, but you can use box2D (which rumor has it that it is being used in Angry Birds).
Good luck.

From my experience there are a couple of social SDKs. One that worked for me is Skiller multiplayer SDK. They take care of the multiplayer protocol and server side so you dont need to mess with this part and only handle the game logic. Currently they support only 2 player multiplayer games which was fine for my game and probably will satisfy your chess game but they said that they will release massive multiplayer SDK soon as well.
Good luck with the game.