If something returns void it means it doesnt actually return anything,
therefore it is a syntax error to try and assign nothing to a variable.  If
you have a look at a method that returns void then you will probably see no
'return' in it, but if you do it will say 'return' and nothing else.
For your example, I would imagine setComment() takes a String as a
paramater, and the designer has decided to not return anything which makes
sense since all you are doing is passing a message in effect.  Some
programmers never return void, instead they take the opportunity to at least
return a boolean for sucess/failure but this is a design choice.
Anyway, the short answer is you cannot store nothing in a variable,
therefore assigning the result of a method that returns void to a variable
doesnt work.

Allan

Not sure what you are asking, but void methods do not return anything,
so attempting to assign something a value from that kind of function
will not compile.

If you need to get the comment from the cookie, I'm willing to bet
there's a function getComment()..

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now with more cowbell