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well hello internet and welcome to part 26 of my design patterns video tutorial this is going to be the final part after covering 24 design patterns today we're going to talk about the visitor design pattern which is often confusing to people but by the end of this tutorial you'll completely understand it and like most of the other design pattern tutorials this is 100% encapsulated so you don't need to watch the other videos if you just want to learn about the visitor design pattern so let's get into it so what is the visitor design pattern well it allows you to add methods to classes of different types however they don't have to be different types but that's just an added level of complexity without much altering to those classes this allows you to make completely different methods depending upon the class that is used and to phrase it another way it allows you to define external classes that can extend other classes without majorly editing them so let's look at this in pictures and make more sense of it this is a basic sort of UML class diagram of the visitor design pattern and basically what you're going to have here is the visitor interface and we're going to implement the visitor interface in this very specific example using what is called tax visitor what I'm basically going to do here is act as if no taxes existed of any type on products when you buy them and our job is to implement taxes however implement them in a way so that different types of products being either liquor tobacco or necessity items are taxed in completely different ways and then what we're going to do is create the visible interface and it is going to have a method that every class that implements it being either necessity tobacco or liquor is going to have that accept method inside of it so let's look over here at what the clients going to do to further explain what's going on over here first we're going to create tax visitor which you can see in the lower left hand corner of your screen and then we're going to define one of our class objects so we're going to define milk as a necessity and we're going to say that it has a price of three dollars and forty-seven cents a gallon what then is going to happen is this three dollars and forty seven cents is going to come over here and how we get this double which is a return value is we call visitor visitor using method overloading is going to say okay you passed me a necessity so I'm going to use this very specific form of the method visit and I'm going to perform a tax calculation bounce that back as a double and then that double goes right here which we can of course receive right here what this is going to allow...