Free Hacking Materials

12 Ways to Learn Android Development for Free Web Sites:
1-   Android Official (https://developer.android.com/guide/index.html )
2-   Vogella (http://www.vogella.com/tutorials/android.html )
3-   Java Code Geeks (http://www.javacodegeeks.com/tutorials/android-tutorials/android-core-tutorials/ )
4-   Coreservlets (http://www.coreservlets.com/android-tutorial/ )
5-   Eduonix (https://blog.eduonix.com/category/android-tutorials/ )
6-   ANDROIDHIVE (https://www.androidhive.info/ )
7-   ANDROIDFORUMS (http://androidforums.com/ )
8-   ANDROIDPIT (https://www.androidpit.com/forum/recent )
9-   Androidcentral (http://forums.androidcentral.com/ )
10-   Stackoverflow (http://stackoverflow.com/questions/tagged/android )
11-   LearnersTV (http://www.learnerstv.com/Free-Computer-Science-Video-lectures-ltv461-Page1.htm )
12-   FreeVideoLectures (http://freevideolectures.com/Course/3184/Android-Application-Development )