Best way to do data source abstraction

[Arthur Pemberton]

What is the best way to do data source abtraction? For example have
different classes with the same interface, but different
implementations.

I was thinking of almost having classA as my main class, and have
classA dynamically "absorb" classFood into to based on the extension
of the input file received by classA. But this doesn't seem possible.

Please advise.

Thank you.

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