Android APK to java source code conversion:
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Required tools for conversion:
  i) 7zip ii) dex2jar iii)jd-gui [java decompiler GUI]


1)Rename the .apk file to apk.zip.
2)unzip using 7zip software to folder.
3)unzipped folder will have classes.dex file
4)use dex2jar to by below command:
    dex2jar "D:\classes.dex"
  This will create the jar file in "D:\classes_dex2jar.jar".
5)run jd-gui and  open "D:\classes_dex2jar.jar" jar file.
    This will give you the source code of the APK.

  From jd-gui, we can do File->Save All sources . So that all sources are saved as zip file.Unzip the file to get the source code.