by using java and dot net codes

Have a look at developing for the Android platform

http://developer.android.com/guide/basics/what-is-android.html[^]

Android dev tools
http://developer.android.com/guide/developing/tools/index.html[^]

Setting up your environment
http://developer.android.com/sdk/installing.html[^]


Once you've got all the tools you require, you should have a look at some example android applications

http://developer.android.com/resources/samples/get.html[^]

List of example applications
http://developer.android.com/resources/browser.html?tag=sample[^]


e.g. contact manager source code
http://developer.android.com/resources/samples/ContactManager/src/com/example/android/contactmanager/ContactManager.html[^]