Why selectionArgs must be an String array?

I answered a question in stack overflow and the user that asked the question ask me:

SQlite Query in android using cursor

why i must give my selectionArgs an Array instead its a single value ?

I didn't think about this before and its my question too now. We must use an array when we have only one value for selectionArgs in DB query?

(I hope i right my question in right place)