oo.java

Book book = new Book(
  "How to Ruin Everything: Essays",
  "Watsky, George"
)

// it has multiple methods related to reviews,
// the interface is not related to books in particular,
// it's part of our domain
Review reviews = new BookReviews(book)

// a ReviewGrading has one method that take a review and rate it,
// there can be many implementation of this grade computation,
// depending on the need, MedianGrading(), etc...
// its responsibility is to generate rates for reviews
// that are meaningful to humans that have to choose if
// they want to read a book or not
ReviewGrading grading = new SuccessCoefficientGrading()

// it implements something like cactoos' Text,
// or maybe there could be a more domain specific interface if needed
// it's responsibility is to format nicely all the stats about a review using one grading strategy
Text stats = new ReviewStats(review, grading)

new Mailing(
  new Text("bla bla introduction"),
  stats
).send()