Filter junk files in android

Question

How to find junk files in android. I don't want someone to code for me.

1. I just want to know how could i know whether a file is junk or not.
2. Or what are the criteria for checking a junk files. Or where must be junk files stored .As in windows some files are stored in TEMPDATA and some data is stored in APPDATA. Where does android store these files.
3. And when can i delete these files. These can be shared by some app.How could i know whether to delete it or not.

As this app does.

Answer 1

Due to the security mode in each Android app runs in its own sandbox. Temporary or junk files created by the app are stored in the apps own data folder located at:

storage/data/data/apppackagename 

There may be any kind of file stored in this location including databases and preferences for the app.

This system allows android to remove the files easily when the app is uninstalled, or when the user goes to android settings for the app and selects clear data.

On non-rooted devices no other apps will have access to this folder.

It is possible for an app to write a file to the to external storage on the device. These files will persist after the app has been uninstalled, but you will have no way of knowing where the file has come from and if it is still needed.