Applet Orchard

Decorator Design Pattern

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Welcome to my Decorator Design Pattern Tutorial. The Decorator allows you to modify an object dynamically. You would use it when you want the capabilities of inheritance with subclasses, but you need to add functionality at run time.

It is more flexible than inheritance. The Decorator Design Pattern simplifies code because you add functionality using many simple classes. Also, rather than rewrite old code you can extend it with new code and that is always good.

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50 responses to “Decorator Design Pattern”

  1. revunuru satish Avatar
    revunuru satish

    Good one, thanks

    Reply
  2. Malcolm Bailey Avatar
    Malcolm Bailey

    The UML association in the diagram is *composition*, not aggregation. Aggregation uses an empty diamond.

    Reply
  3. MecchaKakkoii Avatar
    MecchaKakkoii

    Great vid! Concise and very clear 🙂

    Reply
  4. Jackson Rollins Avatar
    Jackson Rollins

    I get that this is for demonstration purposes only so thank you. If I were ever to create a pizza by programming I would have a `Pizza` class with a toppings member that held an array of `Topping`s. `new Pizza([new ThinDough(), new Mozzarella(), new TomatoSauce()]);`

    Reply
  5. armin oldboy Avatar
    armin oldboy

    thank u.

    Reply
  6. yashfernandojain Avatar
    yashfernandojain

    All of these design look exactly the same to me.

    Reply
  7. VIVEK ASHOKAN Avatar
    VIVEK ASHOKAN

    thank you for the helpful tutorial, but i have a doubt. in this pattern, all the toppings implement a topping decorator which are added to a PlainPizza. would it go against the guidelines of decorator design pattern if a have a different class at the same level as plainpizza( i know PlainPizza is the most basic but in a scenario where there was another type of pizza say BasicPizza) that implements Pizza and all toppings are added to it? Do i have to rewrite both PlainPizza and BasicPizza to extend some class XYZPizza than implements Pizza interface to maintain the structure? Thank you in advance.

    Reply
  8. שקד גרינפלד Avatar
    שקד גרינפלד

    one more time,I just have to say!
    you are the best in Youtube…

    Reply
  9. Priyanka Jondhale Avatar
    Priyanka Jondhale

    Why do we need to define methods(getDescription , getCost) for tempPizza in ToppingDecorator Class?? i think It will work fine without that too. Is it ??

    Reply
  10. LunamiiMusic Avatar
    LunamiiMusic

    The GOF book has the component object within the abstract decorator listed as private, not protected. Is there any reason to go with Protected vs private?
    Thanks!

    Reply
  11. restoMAG Avatar
    restoMAG

    I just don't get where's the "adding functionality at runtime" if you can't create a different pizza at runtime.

    Reply
  12. Sarah Tammenga Avatar
    Sarah Tammenga

    Now I wanna eat a pepperoni pizza… But it the tutorial really helped me! Thanks

    Reply
  13. FesliyanStudios Avatar
    FesliyanStudios

    Why not just create methods in the super class that can add price, etc…? Just a newb asking.

    Reply
  14. Yevgeny Avatar
    Yevgeny

    Never heard of three cheese pizza (I've worked in a restau for one summer). Is four cheese pizza is also popular in the US?

    Reply
  15. Ashish Saraswat Avatar
    Ashish Saraswat

    Thanks for the video .. They are really helpful .. Rather than reading the GangOfFour book this is much precise and better to be done over a weekend

    Reply
  16. Justin Almassi Avatar
    Justin Almassi

    you can get an instance of an interface? – you typed 'public protected Pizza' (Pizza is an interface) how is that possible? I thought interfaces were totally abstract.

    Reply
  17. Vimanyu Aggarwal Avatar
    Vimanyu Aggarwal

    +Derek Banas : Filled diamond represents composition not aggregation ! Also, the diamond is positioned near the parent. Kindly correct me if I am wrong.

    Reply
  18. Thien Pham Quang Avatar
    Thien Pham Quang

    What is ThreeCheesePizza means ?

    Reply
  19. MrBeardtard Avatar
    MrBeardtard

    How come in the Mozzeralla or the tomatosauce class there was no declaration of tempPizza, how did java just know?

    Reply
  20. Cindy O Avatar
    Cindy O

    Your voice is so different since this is a 5 year old video, and it really throws me off haha

    Reply
  21. Ramon Brand Avatar
    Ramon Brand

    Is this the same as the "Component" design pattern?

    Reply
  22. Kirk Bae Avatar
    Kirk Bae

    Thank you very much!

    Reply
  23. grungeisdead Avatar
    grungeisdead

    You never thought to mention the language before getting into the video? (Even in the comments…)

    Reply
  24. JamSamJackx Avatar
    JamSamJackx

    Does the ToppingDecorator need to be abstract or can it be just another class that uses the Interface, then topping objects just extend that?

    Reply
  25. flowing in May Avatar
    flowing in May

    Enjoying the videos so far. However, I don't understand how is this different from the builder pattern?

    Reply
  26. floriegl Avatar
    floriegl

    Great video. Really helped me with my presentation in programming.

    Reply
  27. Mohammed Sultan Avatar
    Mohammed Sultan

    Whenever I watch one of your videos, I ask my self "For which company this guy works? Google, Microsoft,….". However, when I see the number of videos you have on your channel , I think you are unemployed 🙂

    Reply
  28. SpMeKP Avatar
    SpMeKP

    You should be hired as a tutor at my college. You just saved me 5 hours to say the least, while providing me with information in the most appropriate way. And this is not the first time…

    Reply
  29. 0x28 Avatar
    0x28

    Abstraction (e.g. the Decorator pattern) is used everywhere in modern programming! In ReactJS, in TypeScript, in custom solutions..

    Reply
  30. 0x28 Avatar
    0x28

    I'm glad I already graduated from my B.Sc. in C.S. I actually hate programming. I'm glad I'm off that boat!

    Reply
  31. Yashasvi Girdhar Avatar
    Yashasvi Girdhar

    What’s the need to use abstract class ‘Topping Decorator’ here? It doesn’t do anything and I think it’s use makes the concept confusing.

    Reply
  32. Jaco Vermeulen Avatar
    Jaco Vermeulen

    I understand how this example works, though I wonder if you would be able to help me understand it better. I am given a class hierarchy where I have a Singly linked list(SLL). Doubly linked list(DLL) inherits from SLL. Now my assignment requires me to implement DLL as a decorated SLL. Any thoughts? I think I do not yet fully understand the decorator as I cannot figure out how I would go about doing this.

    Reply
  33. Dragan Smoljan Avatar
    Dragan Smoljan

    why its important for class ToppingDecorator to be abstract?

    Reply
  34. michi bliblablub Avatar
    michi bliblablub

    Couldn't you just add two properties for cost and description in ToppingDecorator?
    Then you don't need the methods in the subclasses who overrides the superclass-methods.
    ToppingDecorator.GetDescription() would then look like this:
    return tempPizza.GetDescription() + describtion;

    Reply
  35. Fastjur Avatar
    Fastjur

    Great video, one question though. Why did you add the "Adding dough" println statement to the Mozarella class? This should be in the PlainPizza class as this is where the dough is added and the price for the dough (and thus the plain pizza) is calculated.

    Reply
  36. Vignesh K Avatar
    Vignesh K

    Awesome. Much better explanation than HeadFirstDesignPatterns. Hats off.

    Reply
  37. Mr8lacklp Avatar
    Mr8lacklp

    But why would you do that instead of just making an abstract class topping and defining many different toppings and having an ArrayList of those inside your Pizza. If you want to know the price of the Pizza instance now, you just have to loop through the ArrayList inside your getCost() method and add the price of a plain Pizza to it. Same goes for the description. Just call getName on all the toppings. Besides now you coul have all the toppings subscribe to a sales department or something like that and have it manage their prices.

    Reply
  38. Uğur Dinç Avatar
    Uğur Dinç

    To add more toppings, would I have for instance > new GreenPepper(new Spinach(new TomatoSauce(new Mozarella(new PlainPizza())))) ?

    Reply
  39. Daniel Wahlstrom Avatar
    Daniel Wahlstrom

    Great video, but poor example. The main method here doesn't do the design pattern justice. Check out this succinct explanation on SO: http://stackoverflow.com/a/1549777/84873

    Reply
  40. Arthur Chan Avatar
    Arthur Chan

    Hi, Derek can you give me some hints of how to design a sales tax calculator? Say there are two types of products, normal and other, normal has a sale tax of 10% and other doesnt have tax. Also if products are imported, there will be additional 5% tax. Given a list of Products and their quantity, print out receipt just like a cashier machine does. For this simple question, I can just have two child classes derived from Product class but I dont think it is good if I want it to be scale-able, extendable, because later there may be more taxes for different products(which means i have to create bounch more different child classes).

    Right now, what i think is to just have one Product class, and a singleton class of called TaxMap, which contains tax for different products. So when I try to get tax, I will just call getTaxRate(ProductType) from TaxMap.

    Reply
  41. Daniel Grooms Avatar
    Daniel Grooms

    I read this pattern in Gang of Four today, was trying to figure out what the main method would end up looking like, very glad I found this video. None of my classes for my B.S. CompSci covered this stuff and I'm finding it very important for my job now.

    Reply
  42. Onno man Avatar
    Onno man

    why no dutch cheese 😉 😉

    Reply
  43. David Kozák Avatar
    David Kozák

    Derek, thank you very much. This video really helped me understand the DP. I have one question. I can see how to add new functionality at runtime, but I cannot imagine the process of removing functionality. Lets say that I have a composite object of Mozarella,Tomato Sauce and Pizza. How can I change this to just Mozarella and Pizza(Without the tomato sauce) or even simplify it to just Pizza? 🙂

    Reply
  44. Big Freestyler Avatar
    Big Freestyler

    thank you this really helps me in my exams!

    Reply
  45. Nathan Wiles Avatar
    Nathan Wiles

    Wouldn't it be better instead of classes for TomatoSauce, Mozzarella, etc to just have methods with those names that return a reference to the tempPizza? Meaning the instantiation might look something like

    Pizza cheesePizza = new ToppingDecorator().addTomatoSauce().addMozzarella().getPizza();

    That seems much more clean to me.

    Reply
  46. D.OriginaL Avatar
    D.OriginaL

    does the pizza maker HAS to have the main (String[] args)

    Reply
  47. Ksenia Burova Avatar
    Ksenia Burova

    You are the best! Come to teach at UTK

    Reply
  48. İrem Ertürk Avatar
    İrem Ertürk

    rather than creating the Pizza object by nested new statements , is there a way of doing it with factory pattern?

    Reply
  49. Junkzi Avatar
    Junkzi

    The "Adding Dough" Part was cheated 😮 just try a pizza without moz 🙂

    Reply
  50. Martin Kohl Avatar
    Martin Kohl

    Great video on the Decorator pattern Derek! Loved it!

    Reply

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