Retrieve source code from .apk file in Android

1. Download dex2jar file from here.
2. open Command Prompt and change path as : C:\dex2jar and type cd C:\dex2jar and press enter. Place APK file in dex2jar folder after that type dex2jar FlagQuiz_1.1.apk to start decompiling it.
3. Download Java JD_GUI from here.
4. Open the converted jar file. There list of all classes will be displayed