What's the name of the book? Or, if you have a direct link to Amazon, that'd be helpful.
Actor isn't something in the standard library, so without more information, I'm not sure what package it's trying to use. Unless (and this is a strong possibility) it's a custom package designed specifically for the book, in which case Actor would be from an earlier chapter.
Depending on the author, all the code in the book could be (...probably is) online somewhere, possibly on the publisher's site, possibly on github. Either way, the first couple pages of the book would say where the code can be found.
One of the problems with books, in general, is if there's a typo or mistake, they can't fix it. So there will be errata released on the publisher's site saying what the right code is, or possibly reworded explanations of things. Which brings us back to the beginning when I asked which book it is, exactly :p
*edit* OR! If you give us a little more context, like how the Actor class is used (full code helps), we can probably figure out what it's doing and write one close enough to what the code in the book is expecting.
Actor isn't something in the standard library, so without more information, I'm not sure what package it's trying to use. Unless (and this is a strong possibility) it's a custom package designed specifically for the book, in which case Actor would be from an earlier chapter.
Depending on the author, all the code in the book could be (...probably is) online somewhere, possibly on the publisher's site, possibly on github. Either way, the first couple pages of the book would say where the code can be found.
One of the problems with books, in general, is if there's a typo or mistake, they can't fix it. So there will be errata released on the publisher's site saying what the right code is, or possibly reworded explanations of things. Which brings us back to the beginning when I asked which book it is, exactly :p
*edit* OR! If you give us a little more context, like how the Actor class is used (full code helps), we can probably figure out what it's doing and write one close enough to what the code in the book is expecting.