How does "recycle master recycle bin" android app works ?

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Java

Mobile

Android

I am trying to find how does recycle master recycle bin app works , what it really does is recover deleted files in android device and it does not use rooting.
there are several apps with rooting but this one in particular is good but what is the functionality of getting the files and recovering them is done pro-grammatically or what is the flow or approach to follow to create such an app.
I am not an expert developer and no tutorials on this matter so any guidance can be helpful.
I am using android studio and know java.

What I have tried:

researched on disk digger ,dumpster apps.