WHY JAVA ?

Google  : Currently, all apps have the ability to read the external storage without a special permission. However, this will change in a future release. If your app needs to read the external storage (but not write to it), then you will need to declare the  READ_EXTERNAL_STORAGE  permission. To ensure that your app continues to work as expected, you should declare this permission now, before the change takes effect. However, if your app uses the  WRITE_EXTERNAL_STORAGE  permission, then it implicitly has permission to read the external storage as well.

My implementation of the Switch Button allows you to change  the on and off state !

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To prevent someone from accidentally instantiating the contract class, give it an empty constructor.