Visitor patterns

- In this video, we'll implement the Visitor Pattern.…As described in this article from DZone.…First, we'll copy some classes and interfaces…from the article.…The first is the Visitable interface.…This indicates something that can be visited,…such as a book.…Next, the Visitor interface.…And this is an object, that will do the visiting.…In other words, it will visit a Visitable.…The Book class, implements the Visitable interface.…

Visitable has one method,…and Book implements the accept method.…We'll implement the PostageVisitor class,…and it implements Visitor.…Finally, we'll test all of these.…In the before method, we'll populate the VisitableList.…We'll create items.…We're instantiating the type…private ArrayList Visitable items.…We'll create a new Book, and add it to the list.…

A second new Book, and add it to the list…We'll create a test, testPostageCalculation.…We'll calculate an anticipatedResult.…Then we'll actually calculate the Postage using this method.…And finally, we'll assert that they're equal.…We'll run the test.…