What is the Strategy Pattern? (Software Design Patterns)
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- Опубліковано 28 чер 2024
- In this video, learn why the Strategy Pattern is such an important design pattern. I tell you what the strategy pattern is, how it works, and explain it with an example.
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I've made some pretty bonkers class hierarchies because I never thought of doing it this way before. Thanks for the insight!
you explain things very clearly, and I'm grateful for such a high quality video. Thanks! That said, I have some perplexities with the example you're using (maybe because of my limited understanding; please do not take them as criticisms).
1. In my understanding the strategy pattern is not well-suited to the example. If you have to create a "NoFly" class for the RedDuck, then you're not much better off than the initial suggestion of overring the fly() method in the RedDuck with a "do nothing" method. If the RedDuck cannot fly, in an ideal design one shouldn't tell it how to fly at all. Also, every time I instantiate a RedDuck, I have to remember to pass it the "NoFly" object, but nothing prevents me from passing it another flying strategy. Surely design patterns should "design out" possible bugs, but in this example this doesn't seem to be the case to me.
Wikipedia reports, on its "strategy pattern" page, a different example which looks much better to me. It's about a restaurant bill, containing a List of orders and prices, and the "strategy" concerns possible discounts applied to the prices. In this case too there is a "NoDiscounts" strategy, but the situation to me is different. There's only one class, RestauntantBill, and naturally all RestauntantBill instances need to know what discounts should be applied ("no discounts today" is a reasonable strategy); on the other hand the "duck" example mixes the strategy pattern with inheritance, IMHO.
2.If your example the performFly() method takes no arguments and just prints out a string. This is not wrong, but in many example of the Strategy pattern the "Strategy" method actually changed the internal state of Duck class they belong to, ie they are of the type performFly(this). This took me some time to get my head around, and I think a full explanation should also comprehend this more complex situation.
3. I personally don't really like these examples with Ducks, Dogs, Animals and so on. I'd much prefer a realistic (or at least semi-realistic) situation. This is because, with the Ducks example, I have to do an extra abstraction effort to remember what the heck I want to do with these essentially meaningless classes and methods. But this may be just me.
In any case thanks again for the video. Regardless of whether my observation has a basis or not, just reflecting on these things helps understanding.
Very good comment, i think almost the same, especially your 1.point.
Creating a Dummy Method feels wrong, but after thinking a while, i think thats not that bad.
See it as a Finance Balance Sheet, you getting all Benefits, and If one concrete Claas has a slightly different Behaviors, thats the price you gonna need to pay.
At some Point you need to Code the exception , If you otherwise want to Profit from all the benefits.
What Brothers me more, is that the concrete Claas has a fly Method, but it will never get called, even worse, it could be missleading for the client. One option my be to make the instance variable optional ?
FlyBehavior fb: IFlyBevahior | null.
Will this Work or has someone an elegant solution for this ?
Yes I think creating a dummy NoFly class is bad because it violates Liskov Substitution principle. Because you are expecting a call to fly method to result in a fly, but this implementation does nothing.
you just made OOP better for me to understand now. I use C# and my instructors could not simply this concept at all. Thank you!
Thank you for a simple example! Got my OOP exam coming up and this was really helpful :)
You're very welcome! I wish you the best of luck on your exam!
You are the best! Please more Design Pattern content.
It would be great to include some real world examples and other content that's extra to the book.
Thanks for the suggestion Will. As I noted in another comment, I've already recorded part 2 which is on the observer pattern using an example from the book. Going forward though, I will try to use more relatable examples. Thanks for watching!
Unfortunally, I didi not finish all the patterns of the book. You were GREAT!!! Your explanations are AWESOME!!!!
Reading the book and coming here, gave me a better understanding of this pattern. Appreciate your teaching..
Thank you for this crystal clear explanation, please keep going to upload more patterns 👍
Thanks bahadir! More coming every week :D
@@BeABetterDev plz continue, I love way of explaining
Hi, thanks for the great toutorial, I just had one question, by including the instance variable in base class is it breaking liskovs substitution principle? Because now every derived class knows about the fly method and it needs a implementation even if it does not know to fly?
It is not breaking liskovs substitution because the parent Duck class is the one which implements the FlyBehaviour, in this case the subclasses aren't forced to implement the interface but simply invoke the methods from the Parent class which makes sense to them.
Thanks is great! excited for the next videos and might even get the book to follow along
Thanks Raymond! I can't say enough positive things about the book. Even though I'm already familiar with all the patterns, I'm learning something new with every chapter. For those just getting started with Design Patterns, I would consider this an essential read.
Thanks again for your support!
Very crisp and to the point tutorial and wonderfully explained, learned a lot. Thank you.
Glad it was helpful Arun!
awesome presentation, love it, really learnt a lot, more power!
Thanks for explaining these pattern.
Nice video. I have a question, if I need to add one more function like colour of the beak then do I need to pass two objects of two interface while creating mallard duck object. Or how should we proceed with it?
Thanks for the video. I like using a video game example where you have different types of Adventurers who need interchangeable BattleBehavior strategies.
Thanks Consilium! The video game example works well!
Thanks, this is really helpful. Please do more videos about design patterns.
Is this not just dependency injection, essentially?
You're excellent explainer of concepts. Request you to make all 26 design patterns. Thank you
awesome video, I just purchased my book a little while ago, I know how to code in all basic functions to strings, booleans to OOP, always was stuck on how to code in the pattern etc.. i think this book will help
Thanks Mystical Road Man! I find doing the exercises really helps. It helps drill the concepts into your mind and gives you a sense of muscle memory.
Top-notch explanation. Thanks a lot
Thank u so much, this the best explanation !!!!
You're very welcome!
I really don't understand why nobody gives real world examples
Yeah, ive been badly searching for a good video which explain when to implement this pattern in the real world.
Great!!!. Please make a video on facade design pattern
I was looking for composite design pattern in ur play list .... Can u plz make one ? Btw u r jus super
What program are you using the stylus with?
Nice tutorial, as usual. But I am impressed how nice your handwriting is :) I purchased wacom tablet to try something similar, but boy oh boy is my handwriting unusable :D
I have to stick to drawing lines and circles for now..
Hah the handwriting on a tablet takes a little practice to get used to - definitely more difficult than I was expecting. And thank you for the kind words!
when will continue this series enjoy it to the max really
Wow, you just happened to publish this video the same day that I was looking for just this. Thanks! Looking forward to the rest
Thanks for the video. Please create more videos for other patterns ...
Coming soon! Thanks for watching.
@@BeABetterDev Much awaited :)
With java8 , default and staic methods can have body and the same can be reused in multiple classes implementing the interface, the issue with fly() method will not arise and we will bypass the complexity and a chance of multiple inhertance(multiplier parent class), Is there still space for strategy pattern?
can we use default methods of interface instead of using strategy patter?
best explanation
Thanks Monika!
Hi! What do you use to show your whiteboard?
Hi lo, I use photoshop but I used to use SmoothDraw (free). I created a video on how to set it up too if you are interested: ua-cam.com/video/6Fk9xDpJhvk/v-deo.html&lc=UgzhB5GLwHY-8hGYsxN4AaABAg
@@BeABetterDev Oh, man! You explained everything I wanted to ask! Thank you a lot for being so open to sharing info
Amazing
Thanks!
Does Collections.sort(Collection, Comparator) use Strategy pattern?
rather than using dependency injection, function to set fly behavior in Duck class would be better I guess. Doing that if we have to add another behavior we just have to add another function to set rather than adding dependency everytime when adding a new behavior.
Bro Amazing turorial but you almost left me blind with that IDE
lol! I'm so sorry - I prefer the white :D
Can you tell the page no from the book? I'm not able to find strategy patters in Head first design pattern book.
What program did you use to draw on the screen ??
Hi Bowe,
In this video, I used Photoshop. However in the past, I used a program called Smoothdraw which is free and very similar. I made a video on it here: ua-cam.com/video/6Fk9xDpJhvk/v-deo.html
Hope this helps.
Is this a good book if I'm learning js?
Payment method could be example of it
Am I right in thinking that Java lambdas would be well suited to this pattern?
This creates dependencies on constructors, so this should maybe be used together with a Builder
I am studying my software design pattern exam with these videos and this videos are very pure and helpfull than my teacher. Thank you bro, keep going
Thank you so much Berk. Comments like these mean a lot to me and motivate me to keep on making more content. Thanks again and good luck on your exam!
I didn't find how RedDuck is implemented in the code. Other than that, it is clearly explained.
I'm so glad I abandoned OOP six years ago, and I will never going back to that hell.
Beauty is in the eye of the beholder!
Holy shit I finally understand singletons and dependency injection
Great to hear Doda!
Ducks fly with wings last time I checked as well😉😂
Hah, good catch :D
Good job, but are you allowed to reuse a book so closely for your own content? I wouldn't want you to get in to any trouble for this. I understand that it also kind of promotes the book.
This is a good question Will. I'll have to check this out. Thanks for bringing this to my attention.
In this example why not just assign the "flyWithWings" behavior to all Mallard ducks in the constructor for MallardDuck?
Cedrick Mccrary the one who structure the strategy to these two components. gang gang
@evanwest4751 is acts like a massive Baguette
Is this what Guice did？
I don't like the example. How a duck flies isn't separable from the duck. I would do something like say you're building a robot and it could have wheels that roll or legs that walk and they both implement a move interface.
Also the joke you missed would be if one of the ducks flew Delta or some other airline.
I'm just learning but I think your example is not entirely correct. As you did it, every duck has to fly because you are taking the instance FlyBehavior into the constructor of abstract class Duck. What about ducks that do not fly and do not need FlyBehavior? I think a possible solution would be to create the second constructor of the abstract class Duck without instantiating FlyBehavior.
Isn't this just composition?
Duck walkerDuck = new walkerDuck(what am i supposed to pass here ); ?
Yes, I think he made a mistake. As he implemented this, every duck h a s to fly. I think he should have used the second constructor without FlyBehavior.
"Real life scenario", then the silly duck thing? To me that is not a real life scenario.Real life implies something you might actually use like input or output of data in json, csv, or yaml, or if you wanted to stay academic, calculating grades based various grading schemes. There are probably hundreds of other simple examples. Personally I find examples i can imagine using much more inspiring than abstract caricatures of algorithms.
You arrows are backwards and denotes 'has a' instead of 'is a'. Very bad.
Thanks for pointing this out. I've corrected this in my upcoming videos.
No fly... breaks skateboard
god, I forgotten how ugly Java was...
beauty is in the eye of the beholder!
So... I dont see why the first example of simply implementing a flyable interface is so terrible.
Personally find this book abhorrent.
3 minutes of bla bla bla. Please reduce the introduction
PHP code example of strategy pattern:
github.com/8ivek/design_patterns/blob/main/03%20Behavioural%20design%20patterns/01%20Strategy%20Design%20Pattern/main.php
comments are welcome.