Strategy Design Pattern
HTML-код
- Опубликовано: 23 авг 2012
- Code is Here: goo.gl/TqrMI
Best Design Patterns Book : goo.gl/W0wyie
MY UDEMY COURSES ARE 87.5% OFF TIL July 16th ($9.99)
www.udemy.com/
➡️ Python Data Science Series for $9.99 : Highest Rated & Largest Python Udemy Course + 56 Hrs + 200 Videos + Data Science bit.ly/Master_Python_35
➡️ New C++ Programming Bootcamp Series for $9.99 : Over 23 Hrs + 53 Videos + Quizzes + Graded Assignments + New Videos Every Month bit.ly/C_Course_35
I LIVESTREAM CODE HERE : / derekbanas
MY DISCORD : / discord ( Contact Me Anytime )
Here is my Strategy design patterns tutorial. You use this pattern if you need to dynamically change an algorithm used by an object at run time. Don't worry, just watch the video and you'll get it.
The pattern also allows you to eliminate code duplication. It separates behavior from super and subclasses. It is a super design pattern and is often the first one taught.
Learn in One Videos for Every Programming Language
Subscribe to Bookmark them: bit.ly/2FWQZTx
C++ : ruclips.net/video/Rub-JsjMhWY/видео.html
Python : ruclips.net/video/N4mEzFDjqtA/видео.html
Java : ruclips.net/video/n-xAqcBCws4/видео.html
PHP : ruclips.net/video/7TF00hJI78Y/видео.html
MySQL : ruclips.net/video/yPu6qV5byu4/видео.html
JavaScript : ruclips.net/video/fju9ii8YsGs/видео.html
C# : ruclips.net/video/lisiwUZJXqQ/видео.html
HTML5 : ruclips.net/video/kDyJN7qQETA/видео.html
CSS3 : ruclips.net/video/CUxH_rWSI1k/видео.html
JQuery : ruclips.net/video/BWXggB-T1jQ/видео.html
TypeScript : ruclips.net/video/-PR_XqW9JJU/видео.html
ECMAScript : ruclips.net/video/Jakoi0G8lBg/видео.html
Swift : ruclips.net/video/dKaojOZ-az8/видео.html
R : ruclips.net/video/s3FozVfd7q4/видео.html
Haskell : ruclips.net/video/02_H3LjqMr8/видео.html
Handlebars : ruclips.net/video/4HuAnM6b2d8/видео.html
Bootstrap : ruclips.net/video/gqOEoUR5RHg/видео.html
Rust : ruclips.net/video/U1EFgCNLDB8/видео.html
Matlab : ruclips.net/video/NSSTkkKRabI/видео.html
Arduino : ruclips.net/video/QO_Jlz1qpDw/видео.html
Crystal : ruclips.net/video/DxFP-Wjqtsc/видео.html
Emacs : ruclips.net/video/Iagbv974GlQ/видео.html
Clojure : ruclips.net/video/ciGyHkDuPAE/видео.html
Shell : ruclips.net/video/hwrnmQumtPw/видео.html
Perl : ruclips.net/video/WEghIXs8F6c/видео.html
Perl6 : ruclips.net/video/l0zPwhgWTgM/видео.html
Elixir : ruclips.net/video/pBNOavRoNL0/видео.html
D : ruclips.net/video/rwZFTnf9bDU/видео.html
Fortran : ruclips.net/video/__2UgFNYgf8/видео.html
LaTeX : ruclips.net/video/VhmkLrOjLsw/видео.html
F# : ruclips.net/video/c7eNDJN758U/видео.html
Kotlin : ruclips.net/video/H_oGi8uuDpA/видео.html
Erlang : ruclips.net/video/IEhwc2q1zG4/видео.html
Groovy : ruclips.net/video/B98jc8hdu9g/видео.html
Scala : ruclips.net/video/DzFt0YkZo8M/видео.html
Lua : ruclips.net/video/iMacxZQMPXs/видео.html
Ruby : ruclips.net/video/Dji9ALCgfpM/видео.html
Go : ruclips.net/video/CF9S4QZuV30/видео.html
Objective C : ruclips.net/video/5esQqZIJ83g/видео.html
Prolog : ruclips.net/video/SykxWpFwMGs/видео.html
LISP : ruclips.net/video/ymSq4wHrqyU/видео.html
Express : ruclips.net/video/xDCKcNBFsuI/видео.html
Jade : ruclips.net/video/l5AXcXAP4r8/видео.html
Sass : ruclips.net/video/wz3kElLbEHE/видео.html
An example of this pattern with Dependency Injection would be great.
Can we get a tutorial on Spring Boot and Kafka?
jesus, what do you not know?
This video is amazing because
1.you supplied code
2.you tried a wrong approach first which made me think why using this design pattern is important and when to use it
3.learning by example and my diagram at one video
4.your teaching style is clear ( little face paced for a beginner like me )
thanks very much i really needed to learn patterns
+Daedlues Thank you for the nice compliments :) I'm glad it helped.
@@derekbanas Sos un fenomeno Derek!
For someone who's not a beginner like me, all those points hold true but his speed is amazing. It's exactly the right pace.
He also has magical powers by making a dog flies, amazing!
For my perspective and point of view. This tutorial is bad because he shows a bad way to code and then does everything on top of it. For a begginer it might be hard to grasp what is where.
I like how you explain the bad practice code before presenting the design pattern. This way we know when to use it.
Alex Toma Thank you :)
You're very welcome :) Yes it takes a while to learn how to properly use patterns. Eventually programming stops being a set of commands and rules and instead becomes an art form in my opinion. With a bit of practice you'll soon start making master pieces
Yes you can often use an Enum in this situation, but it will limit flexibility which is normally what you aim for with most design patterns
I realise how bad Uni lectures are. If i finish my Degree its because of RUclips.
+billyblackburn87 I'm glad I could help :)
I understand you men, I'm studying at ESCOM in México.
@@derekbanas Yeah seriously I'm using your videos right now to study for an exam, my teacher spent a 3 hour course on 3 design patterns but you went over one in 11 minutes and I understood better.
@@todarfclips vf
Have you finished your degree?
Here are all my UML tutorials and codes in one place newthinktank. com/videos/uml-video-tutorial/
I hope you like it :)
I'll cover that in future tutorials. The short answer is that it depends on the situation. The object oriented analysis tutorial is in the works. By the end I'll cover everything oop. Thanks for watching
Bog vas blagoslovi, kot dobro. Hvala
Where can I get PPT used in this video?
i thought i would come revise my design patterns in java since its been quite some time and guess where I landed :D :D :D fantastic one mate,
slidenerd Thank you. Nice to see you :) Keep making those great videos!
I included the classes that implement flys on the same page as I created the flys interface. You'll see it if you look over the code on my website. Sorry about the confusion. I normally don't do that in tutorials
Thank you very much :) I do my best to constantly improve. Sometimes in doing so I make a bad video now and then, but I think it is worth it. I plan to eventually make a tablet app for every tutorial series that will provide a quiz and animations to improve the learning process. I have started doing that a bit in recent tutorials. Most of the money I make from these videos goes back into making better videos. Thanks for the nice comment!
It is awesome to be able to help people all over the world :) Thank you for telling me you are watching!
Extremely helpful. Really well put, well designed and such a good example! At it's most basic level. Good editing too. I'm sure it must be hard to squeeze it all under 15 minutes.
Thank you for the compliments :) I'm glad you liked it
Here is my UML Tutorial Playlist ruclips.net/video/OkC7HKtiZC0/видео.html
I also have a Object Oriented Design Tutorial in which I show how I solve problems ruclips.net/video/fJW65Wo7IHI/видео.html
Both are on my RUclips channel. I hope you find them useful :)
Hi Assil, I'm not sure what you mean by website type? I try to use Wordpress if the site is simple. If not, I use a PHP framework the vast majority of the time. I lean towards Java and C / C++ application wise.
Hi Derek,
Thanks a lot for your channel, it helped me a lot in my job interviewing process.
I owe you one ;-)
Well...this playlist has helped me better understand design patterns than 2 years of college. You deserve many beers. Many many beers :D.
Thank you very much :) I'm happy that I could help.
Thank you very much :) In the refactoring tutorial I spend a good amount of time answering design pattern challenge questions. That was a lot of fun
You're welcome :) I can't wait to cover C++ and the differences that occur with these patterns. They are very similar as you said, but there are slight differences. The same is true with C#. I'll get to it as soon as possible. i promise to cover C and C++ as completely as I have done with Java
You have the teaching gift! God Bless you even more than you have been till now! Thank's for the charity with the humanity by giving away all that high quality high valuable knowledge of yours!
Thank you for the very kind message :) May God bless you as well.
@@derekbanas in Flow
Great video and great series. Two questions:
1. Would you care to elaborate about 2:49, "Avoid Interfaces that Just Force Action"?
2. What is the literature on design patterns in general? Perhaps what GoF published back in the days, or maybe there are newer and better books about the patterns?
Hopefully you still read comments 7 years later ;)
Nope, he didn't read this comment
1. That means you should not add an interface which merely forces yourself to manually determine what every single animal will need to do with flying capabilities. An interface might be more appropriate for an action which would have a distinct implementation for each class.
Thank you :) I have a UML tutorial and I'm going to revisit these patterns again in my code refactoring tutorials that will start next week.
Thank you very much :) I constantly do my best to improve them. I'm very happy that you enjoy them
At 3:12 you state that super class change shouldn't affect subclasses but later you left flyingType uninitialised forcing every subclass cunstructor to set it's value. Shouldn't you just provide a default?
Yeah, i think this is a bad aspect of the pattern. If you, as a developer, were unaware that you need to initialize this, you won't get a compile time error. Or, if you provided a default, at least in this example, you might have flying dogs by accident in production.
Instead of having variable initialized by default, we must have explicit constructor for initializing all the strategy variables in the class, all such classes should not have default constructor for them , which has variables of interfaces in them.
I think that the Strategy Pattern has less to do with Super vs. Sub-classing and more to do with being able to change/substitute algorithms at runtime. In other words: It allows you to avoid hard-coding one particular algorithm (or implementing several and using conditionals to select between them) at compile-time and, instead, dynamically select the most appropriate at run-time.
The Strategy Pattern basically lets you implement behavior (ie. an interface), where ever you find it most appropriate, and then it allows you to easily change that behavior. So for instance you can implement an I/O interface, which is initially text-only (all over), and then dynamically change it to a GUI interface; without re-compiling and without duplicating lots of code.
Hi Derek Banas! It was a bit difficult for me to understand this line of code 'public Flys flyingType;' on 5:31th minute.
As I understand it is field variable, and first we have to declare visibility which is PUBLIC then type, which should be some type like integer, String.. or void. After that goes name which is Flys, however in your case it is first visibility which is PUBLIC, then name Flys and then type FLYINGTYPE (I still can't understand what type is it) This line of code is breaking my logic))) However, I have not read about COUPLING which you mentioned in video.
Abbos-Ali Mirkhanov By using composition to store flyingType I'm able to change capabilities at run time. We can then define the flyingType by passing it to setFlyingAbility and then tryToFly automatically executes the proper code without having to define anything at the beginning.
Flys is not name, its type in this case. There is an interface Flys, and the variable flyingType is of this interface's type - Flys. The name of the field variable is flyingType..
Flys is actually the type of the object and FlyingType is the name of the object. You said correctly, that it's a field variable, means there's nothing declared (no memory has been allocated).
The point of this is,
to define every class that extends from animal whether it can fly or not.
Abbos-Ali Mirkhanov you should focus more on your programming understanding before you pay attention to design patterns mate
shouldnt flyingType be private? maybe that's what he meant?
Thank you very much :) I plan on doing a performance testing tutorial. I do that to a certain extent with the refactoring and algorithm tutorials. I talk about Big O notation and such
I know I've simplified it and in doing so assumed that viewers would understand that there normally would be more than 2 choices. I do that because I'm planning to provide concrete examples in the future on when and how to use these patterns. I hope that makes sense
I think the better way to implement it, is to create another subclass FlyingAnimal that inherits from Animal and let bird inherit from it instead of from animal.
ronenfe Can't have multiple inheritance in Java. Sorry lol .
ronenfe said "instead of Animal". so it is still single inheritance
On the Derek's "When to use strategy pattern" slide, there is a point called "When you need to use several behavior dynamically". Dynamically means at run-time. So, while you can create another subclass FlyingAnimal that inherits from Animal and let the bird inherit from it and dog inherit from Animal class, what happens when your dog, by some magical way, obtained wings and now can fly? If we went with your proposed way of doing things, then there is pretty much no way of telling the class that the dog can fly now. If we went with the strategy pattern as in the Derek's video, we could easily change the flying ability by passing another implementation. Although I admit that the example is a bit silly, the pattern definitely finds its uses in modern development.
Following the whole tutorial and type each line code manually. If anyone need the the source code, I upload them to:
github.com/jiapengjun/designPatterns
Sting Jia He has it in his website.
+Sting Jia cool, thanks a lot)
You're very welcome :) Yes you can create an instance directly in the methods attribute. It is a little odd I know
Thank you :) I do my best to make the videos fast and compact. I'm glad you liked it
Seems like bad code when Dog is forced to set flying ability, a behaviour it shouldn't have.
+XPopCornX
I was thinking the same thing. It seems to me that creating a FlyingType class and slotting it in between Bird and Animal in the inheritance chain would be better. Dog would never have to know about it.
+vnie1988 but then dog can't fly even if it takes jet pack =) or if dog will mutate in some crazy flying doggybird )).
+XPopCornX You could easily set the default flyingAbility to CantFlys to avoid this problem
+XPopCornX I was thinking that maybe the reason it's called strategy pattern is because you're going to define the different strategies in order to implement (achieve) the method.
If I implement a Flying interface I guess a more understandable example would be that in the noFly strategy, the animal boards a plane.
So in that way, the animal can achieve or implement the interface, but using a different strategy. And there are many other strategies that could be thought of to implement an interface.
The real world scenario that I'm thinking about with what I learned here is: databases. There are databases that write to a file (like sqlite), but other databases behave differently. So maybe a strategy pattern would be an interface to store data. We want the same thing (to store data), but the strategies are different.
hahhahaha
it's : Flies ..
You're very welcome :) Thank you for watching
It is in the works. It will come out immediately after the design patterns tutorial. Then I'll cover oop analysis and UML. The refactoring will follow that
You would use it with classes that are very similar. What you referred to is the skill one must develop after learning about patterns. Knowing when not to use a pattern is just as important as learning when to use them. I cover more on that in the refactoring tutorial.
Thank you :) Yes, I tend to make videos for intermediate programmers. Most everyone else aims at beginners so I like to be different.
Thank you :) Yes programming to an interface is most always the best decision. I only use abstract classes when I must implement some nonabstract method
Thank you for telling me you like them and that they help PHP programmers. I always wondered how well they would translate for languages other then java, C# and C++. Im very happy that they've helped
These are by far the most helpful tutorials on RUclips for programmers. I am a first year computer science student and I have been spending hours in the library trying fully grasp structures of programs and object oriented programming. Great videos!
I do use setFlyingAbility in the code sparky.setFlyingAbility(new ItFlys())
Yes you could set flyingType as private. I didn't do that only because I wanted to show 2 ways to set that value. Sorry about the confusion
For every case we can build a class that performs a certain action instead. You can see an example of this in my Abstract Factory tutorial. I define classes for all the potential weapons and engines for my space ship. We have a class implement an interface and then execute the right version of that method based off of normal inheritance. Does that make sense?
Thank you :) then you would access them using a getter method. Is there any reason that wouldn't work?
I should have explained myself better in the tutorial. I now realize that it can sometimes be confusing when I show multiple ways to do the same thing in a tutorial. I'm very happy that you enjoy the videos :)
Yes you are correct. I wish I could have come up with a better example, but I wanted to keep everything as simple as possible
Yes a java enum is often well suited for that.
Thank you :) I did my best to cover just about everything in one video. I'm always very appreciative of the kind compliments!
Thank you very much :) It is very nice to be able to help people understand this stuff. Many more videos are coming.
Thank you :) I did my best to make it understandable by looking at it from a bunch of angles.I'm glad you liked it
Thank you for the kind words :) You have no idea how much I enjoy doing this. It is great to be able to help people!
Thank you very much :) It is really amazing that techniques developed decades ago are still not used in many software companies?
Yes it is halfway between a regular class and an interface
Yes you can implement this in C++. You create a java like interface with a class that contains only virtual methods. Here is some information on abstract classes in Python python. org/dev/peps/pep-3119/
I'm definitely going to cover UML 2.0 so that I can dive deep into oop design principles. Thanks for the request :)
Great! I'll get the last few up this week. I'm glad they are helping :)
You're very welcome :) If it helps make your code more understandable then do it. There is a misconception that there is only one way to use each pattern. Even the GOF book states that it is but a guide and the patterns should be adjusted based on need. I hope that helps
it's 2022, Aug 1, I am watching this almost 10 years later . And it makes so much sanse. Thank you a lot for this video man. A true gem indeed.
Thank you :) I’m happy it is still helping people
Thank you :) I'll get another up as soon as possible
Thank you very much :) I work hard to make the best tutorials I can. I'm glad you like them
Composition is a major part of most of the design patterns, so I can't really assign that just to the strategy pattern. Design patterns in general try to add flexibility through avoiding high coupling in many ways that are quite similar. Inheritance should be avoided if at all possible, but above all else understandable code is the goal
I'm a junior dev, and I picked up a lot of intuition along my programming years. I haven't heard of this pattern before, and I realized that I just wrote a piece of code yesterday that follows this design pattern after not being satisfied with a more traditional polymorphic implementation. Nice.
Thank you for your work as a RUclips educator, I really appreciate your videos. Cheers.
Thank you very much :) That is a much appreciated compliment. I do my best to present these topics in an interesting way
Thank you! I'm preparing for the midterm - videos are really helping me out!
Hey Derek, I would like to thank you to the core. I haven't seen any video tuts on youtube with code. So helpful. Really exiting after seeing your tuts. Thanks alot.!!!
I'm glad you found them useful :)
Thank you very much for taking your time to show your appreciation :) You have no idea how much I appreciate that! I'm very happy to have been of help
Thank you :) I did my best with it
Hi Vishal, Thank you :) I'm glad you found it useful. I record with Camtasia 2 and I edit with iMovie.
One marvellous from our times is that we can simply search for whatever input and quickly find a highly capable professor like you, explaining a fairly simple concept in a much simpler way, in just 11 minutes, with a clear enough voice to be understood at 2x speed. Many others would take a 60 min class, or even more to explain the same. Thanks!
Thank you for the nice compliment :) I appreciate it!
This is the easiest tutorial about design pattern that I have viewed. I can't wait to finish viewing/learning from your tutorials.
+chiligarden Great I'm happy that it helped :)
Thank you for taking the time to write such a nice message :) I very much appreciate that.
Thank you very much :) I used to work as a software architect and part of my job was to train new hires and answer their questions. I'm basically doing here what I did with trainees. I'm not a professor
Anytime you need to restrict a class you would need an abstract class over an interface. An interface really doesn't have any rules. So for example let's say you had a class that represented a printer. You know you'll have to stop printing if there is no more paper, or ink. That will always be the case no matter which printer you use. So an abstract class would provide those limits. Does that help?
Thank you very much :) I already have the UML tutorial finished. I hope you like it
It should be an interface because it wouldn't make sense to have a Flys object. Does that make sense?
I finished it. Here is the UML playlist ruclips.net/video/OkC7HKtiZC0/видео.html
Thanks this is the first video that made “favor composition over inheritance” click for me. I’ve always heard that phrase but now I see how it’s actually used.
It doesn't care that it is an interface. That is why the pattern is so great. The interface just does its job by allowing functionality to change dynamically while not effecting the super class. It may take some time to wrap your head around design patterns, but when you do you'll be able to write great code. It took me awhile as well
Sorry I go overboard every once in a while. Over the years you guys out there have taught me to always be on my toes and to not just flippantly provide answers to questions :)
I'll see what I can do about covering the different unix shell versions and commands. I'd like to do it in an interesting way, which I can't think of at the moment
Old is Gold.
Never imagined video from 2012 is still the best one out here
Thank you very much :) Im very happy that you enjoy them.
You're very welcome :) If you take a look at my OOD tutorials and the refactoring one you'll see that my number one goal is to write very easy to understand code. Very often we have to give up on some capabilities if we want to achieve that goal.
Thank you :) I have a Design Pattern, Java, etc. playlist on my RUclips channel. Sorry, if everything is a bit confusing because I have so many videos. I try to aim for 10 to 15 minute videos. I feel that that is the sweet spot for completely covering topics. I know I'm the only person making videos that long. Actually my videos start out at 30 minutes before editing. I'm working to improve them all of the time. Thank you for your insight :)
Thank you so much for those video on Design Pattern. As soon as I see it, I start looking at it and man, I realize I don;t understand in deeper concept even though I have completed projects in school using those concept.
Thank you very much :) I appreciate that. I planned on introducing UML along with this tutorial. The only problem is that I could easily make 20 videos on the subject. I can't guarantee it would be finished. Thank you for telling me there is interest in that tutorial though
Thank you Derek for posting these series of videos
Saikrishna Boggavarapu You're very welcome :)
Thank you for these great videos. I'm a French student and I need to understand how design patterns work. I understand a lot more in your videos than in my university. Thanks again !
It is very nice for me to be able to reach people all over the world! I'm very happy that you're enjoying the videos :)
Thanks for this! Great pacing. Quick, but still thorough. One of the best educational videos I've seen, period!
Thank you for taking the time to watch and to write a nice comment :) I appreciate that
All methods should be marked as private. I don't always do that in tutorials, but instead normally leave them as default which is very much like private. Which methods are you referring to specifically?
I think the answer is that you wouldn't want to ever have code from flys call for any other methods. You could do most anything in regards to class accessing using java reflection. The whole idea of using composition is to lower coupling and make the code more understandable and extensible. If you start using code that does something out of the ordinary then it would make the code less understandable. Can you give me an example of why you would need to do this?
After this third video of the design patterns series I can't wait to watch the rest! Fantastic explanations, thank you!
Thank you for the nice compliment :)
Amazing tutorial, there is lot of stuff cramped in nicely into this short video, felt like completed 50 pages of reading in ease ... Thank u..
That topic is both very simple and also very complicated. First off, you couldn't even participate in high frequency trading because those computers receive and act on information in less than 10 milliseconds. They just look for patterns, price discrepancies and trading errors and try to take advantage of them. Ex. If the price of IBM went up 2 cents it more than likely will go up another 1 cent so, buy it at 197.16 and then sell it at 197.17. Stuff like that
Thank you :) Another one is coming to day
Hi Derek. One of the best tutorials I have ever seen. I would like to point out the things I liked most about the tutorials.
1. Your voice. It just glues me to the tutorial.
2. The tutorial is short, crisp and awesome.
3. Even your comments and replies here is constructive and clear.
4. The code is well documented and very understandable.
Thank you so much. Hats off!!
Yes that should work. You may want to give it a different descriptive name other than fly though
I'm covering c right now and when that's over ill cover c++. I hope I'm able to help :)