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
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.
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
@@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.
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 ;)
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.
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!
I have worked as a software engineer for 8 years and then went back to school & started doing Machine Learning. But when I wanted to revise my old stuff , your videos were the best option. Thanks for the effort and yes! UML tutorial will be great as well.
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!
I'm very happy that so many people around the world seem to be able to understand me :) the funny thing is that in my country I was often used to speak with people from foreign countries. I could always understand them as well. I'm very happy to be able to help
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
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.
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
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.
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
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
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
Done thanks Todo move notes to onenote 9:30 UML diagram It’s a pattern to favor composition over inheritance. Use case: animal superclass, some subclasses fly and some dont. Instead of animal superclass having a fly method (where not all subclasses can fly) and subclasses overriding it to fly/not fly, and instead of having a flies interface that some subclasses implement and some dont (both these solutions are bad and duplicate the flying code or the non flying code), we can have a flies interface (but not have animals implement it directly). Instead we have “ability objects” that implement the Fly interface like ItFlys: Fly or CantFly:Fly. And animal superclass has instance variable (composition) of type Fly (the type of the interface) and subclasses set that instance variable to ItFlys or CantFly polymorphically. We can have many different types of flying, classes that implement the Fly interface like ItFlys, CantFly, FlyWings, FlySuperFast etc
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.
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.
+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.
+XPopCornX You could easily set the default flyingAbility to CantFlys to avoid this problem
8 ปีที่แล้ว +15
+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.
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
I don't know enough to comment on C++/C#, but for PHP they are extremely useful. One of the major reasons that your tutorials are so good are that you obviously go to a lot of trouble thinking/preparing for them beforehand and they are presented very well - which means that the subjects/methodologies you are trying to explain are easily understood. Wish I'd come across your channel earlier!! Thanks again!! :-)
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 TH-cam educator, I really appreciate your videos. Cheers.
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!!
These are by far the most helpful tutorials on TH-cam 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!
Hello, Derek, I am software developer having 3 years experience(Delphi/Oracle Pro*C, PHP(MVC)) and keep failing wtih interviews especially due to lack of understanding about OOP conception and design pattern. I just found your video and it does help me to understand those questions I have asked during interview and I think I will make it better next time. Thank you so much !
Derek, Theses tutorials are life savers. I'm working for a company in a java boot camp accelerated program in which all of my classmates have previous programming exp. except me. To say I'm drowning in information overload would be a understatement. These tut's have helped immensely. God speed!
I spent days looking at different videos and examples of strategy design patterns that never explained or touched base with the instance variable of the interface. There was so many levels of confusion going on. Like how this abstract could extend multiple sub-classes of the interface being you can only extend one class. And why the need for the interface if I was just extending another class. This was the best explanation that I came across by far. Thank you.
Thanks Derek for such a great video. The first time I listen this video. I think I understand something. But when I try to watch it again. I feel I get lost. Here is my understand (which might incorrect) - Strategy Patterns can use when we have objects shared behavior and we want to avoid code duplication. - Instead of put that behavior as a attribute or method in SuperClass (which is bad because subclass have to override those method and this cause code duplication.) So, we use an interface. However using an interface does not mean just to move the method over there (which cause another problem -- each subclass will implement that interface and cause code dependent. (I do not sure I understand this point correctly or not.) So, Derek suggests that we use interface in a new approach: - Create an interface with behavior as a method. (Flys interface) - Then, create classes for each of those shared behavior and implemented method from behavior interface. (Itflys and Cantfly) - next, the SuperClass (Animal) have a new_field and use behavior interface as a data type - after that, the SuperClass (Animal) need to create a method to access to interface method. -- tryToFly() which return flyingType.fly() - and at object subclass construction -- Derek do interface polymorphically. -- flyingType = new CantFly(); // - at run-time, the instance of subclass (Dog) can access to behavior by using method in SuperClass -- trytoFly() which will call fly() method from the behavior class (Cantfly in this case) The benefit of Strategy Method is: a) I can add behavior which unaffected to Object SuperClass, b) As long as the method name in behavior implemented class not change, modification to the algorithm inside method won't cause any issue to the reference subclass. It would be grateful If someone could confirm my understanding or correct me what I misunderstand. Thank you.
The tutorial is great.. Creating an instance of a Fly directly inside the constructor using new keyword leads to more coupling. Instead we can pass it as a parameter in the constructor to use polymorphism
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
Its simple straight and clear. I have just listen only a few of them. I am in progress of listening more of deisgn principles session. Will recommend everyone who wants to learn design pattern... Thanks Derek
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.
Wow, I had totally skipped these tutorials for some reason when your first created them,. Now I just watch the first design pattern and I am just completly amazed! (why did I skip these videos!!)
Thanks for your great post Derek. I really enjoyed your direct example of the Strategy Pattern emphasizing how you have decoupled any dependence from previous videos. Comments detracting from the ultimate goal of discussing the pattern in general, are no doubt valuable in specific business cases but the attention to detail about what is important to the pattern is what I find most valuable in this videos. For those who already appreciate the existence of individual business constraints within a given implementation, you're intentional quality of skipping particular details about , for example, how private or final a method should or should not be be is something in which, I ,for one, find much value. Your willingness to politely discuss via comments with others how your vagueness on certain points might be more invaluably clarified in particular situations is a cherry on top. Please hit me up if you want to discuss cleaning up your content a bit and syndicating for a good cause. I'm willing to pith in on other people's ventures and I am always looking for good coders to pitch in on mine. Thanks again, Anthony Ruffino aruffino84@gmail.com 815-301-7606
You definitely understand my way of thinking in these videos. I always thought it was better to avoid covering the details at times if it gets in the way of the topic at hand. I'm glad you see that because most people don't. I provide everything for free, so if you want to embed the videos, or use the code from my site in any way feel free to do that. I do all of this purely to help people in any way that I can.
Got to thank you for these series. I failed my OOP subject last year (studying Computer Engineering) and this is being a great help. Studying while on my vacations. Thanks alot man.
I've been thinking about covering Extreme / Agile programming techniques. I'm just not sure if there is any audience for that topic? I don't particularly care about views, but I don't want to alienate every viewer. I'll probably do a overview video on the subject and see how people like it. I also want to cover Discrete mathematics because the Khan academy never covered it and it works perfectly with understanding programming.
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.!!!
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
Derek, THANK YOU VERY MUCH!!... you have made an incredible job. The most important fact in my case, is your clarity to talk, i'm from argentina and as you know, this part of the world talks in spanish. I think that i have quite good english, but i saw a lot of tutorials where you barely understand what they are saying... however, your tutorials are excellent in this point. Congrats to you! Keep doing this job... all the developers in whole world are grateful with you.
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
I wanted to leave a quick note before I forget. Thank you so much Derek. Right now I'm in a Software Design class in which we have to learn these really tricky patterns. You do an absolute amazing job at explaining concepts(literally the best tutorials I've ever seen on the web for programming) I hope you continue to do this work and that you'll find a way to spin it into something even bigger than youtube videos(if you haven't already)
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
Don't worry it is easy to get confused by design patterns. It is just a new way of thinking about programming. It may not seem like it now, but after you understand these oop concepts, it becomes very easy to make very complicated systems
to summarize, Use strategy pattern(Composition), when you wanna have behaviours that change DYNAMICALLY. Use Inheritance when the behaviour changes STATICALLY. Right?
I read these up instead of GoF. I have read Head first before but these videos do a better job than anything I know of. Derek Banas , you da real MVP .
Thank you :) Technically Fly should be an interface because in the real world Fly wouldn't be considered an object. I stick with that idea when writing code, but you may find a reason to use an abstract class that I haven't thought of.
flyingType should be private I agree. I didn't call setFlyingAbility in a constructor because I was trying to be as flexible as possible. Well sort of I could have done other things to add flexibility in hindsight. Sometimes while focusing on the pattern I tend to disregard everything because I have this belief in my head that if I focus on optimization that it will confuse people. I hope that makes sense
Wouldn't an easier case to be have a nested superclass? Animal (Abstract) -> FlyingAnimal (Abstract) -> Bird Animal (Abstract) -> LandAnimal (Abstract) -> Dog FlyingAnimal type creates a base fly method that can be overridden.
I never liked paying college fees, because I felt its not worth it. But for your videos, I voluntarily wish to. That is the degree of satisfaction I have. I can't thank you enough.
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.
Excellent. Many Thanks to u. 1. Way of explanation 2. Choosing of right examples 3. Timing All are good. Till now I am hearing about OOP but not able to understand how it's powerful but because of your examples only I could understand how OOP powerful.
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.
Hi, i'm studying computer science at university of tübingen in germany. All i can say ist that because of you i don't have to visit the lectures for software design to be successful. You know how to put the things in a nutshell. Afterwards i still can dive in, in fact even better then.
Hi Derek, I have number of questions: 1. Just to make sure that I understand what I see: in your Flys.java file you have 3 classes? Flys which is interface and 2 classes of Fly/CantFly which implements the fly() method? It is a bit confusing. Why all of the classes are in the same .java file? 2. I read your replies to the comments below and also in your website and I did not understand how the Animal class uses flyingType: Flys as a field? I saw you wrote about composition, but what exactly is composition? Thanks for the great videos! Shai
Well you probably figured it out yourself by now, since you asked your question a month ago. Putting this two classes in the interface JAVA file is just for clarity and (as far as I understood in my short career as java weekend warrior) is the preffered way, something like good practise, as these classes shouldn't be used outside the interface.
1. This is called inner classes. It is convenient to place several small tightly related classes in one java file. You can (and usually should) place each class in separate Java file, because these inner classes bloat code in no time. 2. You can have an instance of a class in a class field. `Flys flyingTipe;` is no different from `List myList;`
Derek. Even though your implementation is technically correct there are few problems. First the strategy pattern should always have the strategy implemented, typically through a constructor. Secondly the use of an interface to implement an in-ability is confusing, it should not be done. A more appropriate example would say an color system where the strategy could be color by RGB, HSV or HSL. In short stratgey must be required, should not be negated
Two birds in a single shot! I am trying to learn Design Patterns for C#, but learning Java too :) Actually 4 birds (Design Patterns, Java, Inheritance and Polymorphism). Excellent example with all these together. Thank you very much. You are the best!!!
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
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.
Yes I should have marked it as private. Sorry about that. I made the UML tutorial. It's on my TH-cam channel. Thank you for the kind words. I'm always here to teach whenever you are in need :)
Thank you :) I have a Design Pattern, Java, etc. playlist on my TH-cam 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 :)
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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
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 realise how bad Uni lectures are. If i finish my Degree its because of TH-cam.
+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?
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
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.
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!
It is awesome to be able to help people all over the world :) Thank you for telling me you are watching!
I have worked as a software engineer for 8 years and then went back to school & started doing Machine Learning. But when I wanted to revise my old stuff , your videos were the best option. Thanks for the effort and yes! UML tutorial will be great as well.
+Saptarshi Mitra Thank you for the very nice compliment :) Here is my UML tutorial th-cam.com/video/OkC7HKtiZC0/w-d-xo.html
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
I'm very happy that so many people around the world seem to be able to understand me :) the funny thing is that in my country I was often used to speak with people from foreign countries. I could always understand them as well. I'm very happy to be able to help
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.
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
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
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!
Hi Derek,
Thanks a lot for your channel, it helped me a lot in my job interviewing process.
I owe you one ;-)
Thank you :) I did my best to cover just about everything in one video. I'm always very appreciative of the kind compliments!
Bog vas blagoslovi, kot dobro. Hvala
Where can I get PPT used in this video?
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
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.
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
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)
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
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?
Done thanks
Todo move notes to onenote
9:30 UML diagram
It’s a pattern to favor composition over inheritance.
Use case: animal superclass, some subclasses fly and some dont.
Instead of animal superclass having a fly method (where not all subclasses can fly) and subclasses overriding it to fly/not fly, and instead of having a flies interface that some subclasses implement and some dont (both these solutions are bad and duplicate the flying code or the non flying code), we can have a flies interface (but not have animals implement it directly). Instead we have “ability objects” that implement the Fly interface like ItFlys: Fly or CantFly:Fly. And animal superclass has instance variable (composition) of type Fly (the type of the interface) and subclasses set that instance variable to ItFlys or CantFly polymorphically. We can have many different types of flying, classes that implement the Fly interface like ItFlys, CantFly, FlyWings, FlySuperFast etc
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.
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
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
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
it's : Flies ..
I don't know enough to comment on C++/C#, but for PHP they are extremely useful. One of the major reasons that your tutorials are so good are that you obviously go to a lot of trouble thinking/preparing for them beforehand and they are presented very well - which means that the subjects/methodologies you are trying to explain are easily understood. Wish I'd come across your channel earlier!! Thanks again!! :-)
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 TH-cam educator, I really appreciate your videos. Cheers.
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!!
These are by far the most helpful tutorials on TH-cam 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!
Thank you :) I do my best to make the videos fast and compact. I'm glad you liked it
Hello, Derek, I am software developer having 3 years experience(Delphi/Oracle Pro*C, PHP(MVC)) and keep failing wtih interviews especially due to lack of understanding about OOP conception and design pattern. I just found your video and it does help me to understand those questions I have asked during interview and I think I will make it better next time.
Thank you so much !
I'm very happy that I could help :) I wish you all the best in your future interviews!
Derek,
Theses tutorials are life savers. I'm working for a company in a java boot camp accelerated program in which all of my classmates have previous programming exp. except me. To say I'm drowning in information overload would be a understatement. These tut's have helped immensely. God speed!
Thank you very much :) i'm very happy to hear that they are helping.
Yes that is exactly it. Also if we can't think of something as a real object then it shouldn't be instantiated.
Thank you :) Yes, I tend to make videos for intermediate programmers. Most everyone else aims at beginners so I like to be different.
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 :)
I spent days looking at different videos and examples of strategy design patterns that never explained or touched base with the instance variable of the interface. There was so many levels of confusion going on. Like how this abstract could extend multiple sub-classes of the interface being you can only extend one class. And why the need for the interface if I was just extending another class. This was the best explanation that I came across by far. Thank you.
Thank you very much :) I'm happy the video learned up a complex topic
Thank you very much :) I constantly do my best to improve them. I'm very happy that you enjoy them
You're very welcome :) I did my best to make the gof book make more sense
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
Thanks Derek for such a great video.
The first time I listen this video. I think I understand something. But when I try to watch it again. I feel I get lost. Here is my understand (which might incorrect)
- Strategy Patterns can use when we have objects shared behavior and we want to avoid code duplication.
- Instead of put that behavior as a attribute or method in SuperClass (which is bad because subclass have to override those method and this cause code duplication.) So, we use an interface.
However using an interface does not mean just to move the method over there (which cause another problem -- each subclass will implement that interface and cause code dependent. (I do not sure I understand this point correctly or not.)
So, Derek suggests that we use interface in a new approach:
- Create an interface with behavior as a method.
(Flys interface)
- Then, create classes for each of those shared behavior and implemented method from behavior interface.
(Itflys and Cantfly)
- next, the SuperClass (Animal) have a new_field and use behavior interface as a data type
- after that, the SuperClass (Animal) need to create a method to access to interface method. -- tryToFly() which return flyingType.fly()
- and at object subclass construction -- Derek do interface polymorphically.
-- flyingType = new CantFly(); //
- at run-time, the instance of subclass (Dog) can access to behavior by using method in SuperClass -- trytoFly()
which will call fly() method from the behavior class (Cantfly in this case)
The benefit of Strategy Method is:
a) I can add behavior which unaffected to Object SuperClass,
b) As long as the method name in behavior implemented class not change, modification to the algorithm inside method won't cause any issue to the reference subclass.
It would be grateful If someone could confirm my understanding or correct me what I misunderstand. Thank you.
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
The tutorial is great.. Creating an instance of a Fly directly inside the constructor using new keyword leads to more coupling. Instead we can pass it as a parameter in the constructor to use polymorphism
Yes it is halfway between a regular class and an interface
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
Its simple straight and clear. I have just listen only a few of them. I am in progress of listening more of deisgn principles session. Will recommend everyone who wants to learn design pattern... Thanks Derek
Thank you for the kind message :)
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.
Wow, I had totally skipped these tutorials for some reason when your first created them,. Now I just watch the first design pattern and I am just completly amazed! (why did I skip these videos!!)
Yes a java enum is often well suited for that.
Thanks for your great post Derek.
I really enjoyed your direct example of the Strategy Pattern emphasizing how you have decoupled any dependence from previous videos. Comments detracting from the ultimate goal of discussing the pattern in general, are no doubt valuable in specific business cases but the attention to detail about what is important to the pattern is what I find most valuable in this videos.
For those who already appreciate the existence of individual business constraints within a given implementation, you're intentional quality of skipping particular details about , for example, how private or final a method should or should not be be is something in which, I ,for one, find much value.
Your willingness to politely discuss via comments with others how your vagueness on certain points might be more invaluably clarified in particular situations is a cherry on top.
Please hit me up if you want to discuss cleaning up your content a bit and syndicating for a good cause. I'm willing to pith in on other people's ventures and I am always looking for good coders to pitch in on mine.
Thanks again,
Anthony Ruffino
aruffino84@gmail.com
815-301-7606
You definitely understand my way of thinking in these videos. I always thought it was better to avoid covering the details at times if it gets in the way of the topic at hand. I'm glad you see that because most people don't.
I provide everything for free, so if you want to embed the videos, or use the code from my site in any way feel free to do that.
I do all of this purely to help people in any way that I can.
You're very welcome :) Yes you can create an instance directly in the methods attribute. It is a little odd I know
Hi Vishal, Thank you :) I'm glad you found it useful. I record with Camtasia 2 and I edit with iMovie.
Got to thank you for these series. I failed my OOP subject last year (studying Computer Engineering) and this is being a great help. Studying while on my vacations. Thanks alot man.
TigasFMS You're are very welcome :) I wish you all the best in your schooling.
I've been thinking about covering Extreme / Agile programming techniques. I'm just not sure if there is any audience for that topic? I don't particularly care about views, but I don't want to alienate every viewer. I'll probably do a overview video on the subject and see how people like it. I also want to cover Discrete mathematics because the Khan academy never covered it and it works perfectly with understanding programming.
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.!!!
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
Derek, THANK YOU VERY MUCH!!... you have made an incredible job. The most important fact in my case, is your clarity to talk, i'm from argentina and as you know, this part of the world talks in spanish. I think that i have quite good english, but i saw a lot of tutorials where you barely understand what they are saying... however, your tutorials are excellent in this point. Congrats to you! Keep doing this job... all the developers in whole world are grateful with you.
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
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 :)
I wanted to leave a quick note before I forget. Thank you so much Derek. Right now I'm in a Software Design class in which we have to learn these really tricky patterns. You do an absolute amazing job at explaining concepts(literally the best tutorials I've ever seen on the web for programming) I hope you continue to do this work and that you'll find a way to spin it into something even bigger than youtube videos(if you haven't already)
nicolasap86 Thank you :) I'm very happy that I could help with patterns. Many more videos are coming and they will always be free.
Thank you very much :) It is very nice to be able to help people understand this stuff. Many more videos are coming.
Old is Gold.
Never imagined video from 2012 is still the best one out here
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 very much :) I already have the UML tutorial finished. I hope you like it
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
Don't worry it is easy to get confused by design patterns. It is just a new way of thinking about programming. It may not seem like it now, but after you understand these oop concepts, it becomes very easy to make very complicated systems
to summarize,
Use strategy pattern(Composition), when you wanna have behaviours that change DYNAMICALLY.
Use Inheritance when the behaviour changes STATICALLY.
Right?
You're very welcome :) it is very gratifying to be able to help people all over the world
I have made a bunch of stock analysis tools and many patterns are involved. Yes the observer is very common. Sorry, but it depends on your program
I read these up instead of GoF. I have read Head first before but these videos do a better job than anything I know of.
Derek Banas , you da real MVP .
sankalp srivastava Thank you for the nice compliment :)
Thank you :) Technically Fly should be an interface because in the real world Fly wouldn't be considered an object. I stick with that idea when writing code, but you may find a reason to use an abstract class that I haven't thought of.
flyingType should be private I agree. I didn't call setFlyingAbility in a constructor because I was trying to be as flexible as possible. Well sort of I could have done other things to add flexibility in hindsight. Sometimes while focusing on the pattern I tend to disregard everything because I have this belief in my head that if I focus on optimization that it will confuse people. I hope that makes sense
Wouldn't an easier case to be have a nested superclass?
Animal (Abstract) -> FlyingAnimal (Abstract) -> Bird
Animal (Abstract) -> LandAnimal (Abstract) -> Dog
FlyingAnimal type creates a base fly method that can be overridden.
Yes that should work. You may want to give it a different descriptive name other than fly though
Thank you very much :) I work hard to make the best tutorials I can. I'm glad you like them
I never liked paying college fees, because I felt its not worth it. But for your videos, I voluntarily wish to. That is the degree of satisfaction I have. I can't thank you enough.
Thanks again for the compliment :) I'm very happy that the videos are helping. My goal is a free education for all
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..
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.
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.
Excellent. Many Thanks to u.
1. Way of explanation
2. Choosing of right examples
3. Timing
All are good.
Till now I am hearing about OOP but not able to understand how it's powerful but because of your examples only I could understand how OOP powerful.
+Krishna Kumar You're very welcome :)
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.
compile, overloading, static and earley; Runtime, overriding dynamic and late.
Hi, i'm studying computer science at university of tübingen in germany. All i can say ist that because of you i don't have to visit the lectures for software design to be successful. You know how to put the things in a nutshell. Afterwards i still can dive in, in fact even better then.
Thank you :) I'm very happy I helped. Won't your professor get lonely though?
Hi Derek, I have number of questions:
1. Just to make sure that I understand what I see: in your Flys.java file you have 3 classes? Flys which is interface and 2 classes of Fly/CantFly which implements the fly() method? It is a bit confusing. Why all of the classes are in the same .java file?
2. I read your replies to the comments below and also in your website and I did not understand how the Animal class uses flyingType: Flys as a field? I saw you wrote about composition, but what exactly is composition?
Thanks for the great videos!
Shai
Well you probably figured it out yourself by now, since you asked your question a month ago. Putting this two classes in the interface JAVA file is just for clarity and (as far as I understood in my short career as java weekend warrior) is the preffered way, something like good practise, as these classes shouldn't be used outside the interface.
1. This is called inner classes. It is convenient to place several small tightly related classes in one java file. You can (and usually should) place each class in separate Java file, because these inner classes bloat code in no time.
2. You can have an instance of a class in a class field. `Flys flyingTipe;` is no different from `List myList;`
Derek. Even though your implementation is technically correct there are few problems. First the strategy pattern should always have the strategy implemented, typically through a constructor. Secondly the use of an interface to implement an in-ability is confusing, it should not be done. A more appropriate example would say an color system where the strategy could be color by RGB, HSV or HSL. In short stratgey must be required, should not be negated
Two birds in a single shot! I am trying to learn Design Patterns for C#, but learning Java too :)
Actually 4 birds (Design Patterns, Java, Inheritance and Polymorphism). Excellent example with all these together. Thank you very much. You are the best!!!
+Phani Raghavendra Prasad You're very welcome :) I'm glad I could help
Jj
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
Thank you very much :) That is a much appreciated compliment. I do my best to present these topics in an interesting way
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 :) I did my best with it
Ok, I'll make one. I want to make an entire software engineer course here and that will definitely be part of it :)
Yes I should have marked it as private. Sorry about that. I made the UML tutorial. It's on my TH-cam channel. Thank you for the kind words. I'm always here to teach whenever you are in need :)
Been trying to get this pattern for a whille, and what are it's advantages, probably the BEST tutorial out there on the matter. Fudge. I'm impressed.
Etienne-Joseph Charles Thank you :) I did my best to make it easy to understand.
Thank you :) I have a Design Pattern, Java, etc. playlist on my TH-cam 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 :)