No, it is not good. It is considered a good practice to have an adapter as a stand-alone class (not nested one) as it will give you the benefit of code reuse.
Also, if you decide that you need a nested class anyway, make it private.
I recommend a book from Head First series: Android Development to help you get basic perception for structuring your apps.
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solved If is good to definition Adapter or view in Activity [closed]