Difference between "android.permission" and "ANDROID.PERMISSION" when use uses-permission in manifest -

when declare uses-permission, meet both of them:

   <uses-permission android:name="android.permission.write_external_storage" />    <uses-permission android:name="android.permission.write_external_storage"/> 

i tried create folder in sdcard each of permission, it's success. demo code:

 private void initfolders() {         file rootfolder = new file(environment.getexternalstoragedirectory(), constants.root_folder_name);         if (!rootfolder.isdirectory()){             boolean success = rootfolder.mkdirs();             if (!success){                 toast.maketext(this, "can't create root folder!!!", toast.length_long).show();             }         }     } 

so, tell me main difference between them?