State Pattern - Design Patterns (ep 17)

Video series on Design Patterns for Object Oriented Languages. This time we look at the State Pattern.
00:00:00 Intro
00:01:50 Example
00:37:50 Definition
00:38:50 Definition in UML
00:43:37 Example in UML
00:51:20 Example in Code
01:10:41 Recap of code example
► The playlist
• Design Patterns in Obj...
► Head First: Design Patterns
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► Design Patterns: Elements of Reusable Object-Oriented Software
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► Great playlist on State Machines (amongst other things)
• Introduction to the Th...
💪 Patreon Community
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📚 Products I Recommend
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[@claudios]

An 80 minute video on a design pattern?! It really is Christmas, thanks Chris

[@ChristopherOkhravi]

Thank you and Thank you for watching 🙂🙂

[@MahmoudHbobati]

singleton pattern is 20 minutes!!! :)

[@TheGGbond]

wtf is wrong with u

[@calexito9448]

@@TheGGbond reversed card actually

[@openyourmind1694]

I usually watch various tutorials, so I feel capable of giving a "competent" judgment: you have excellent presentation, comprehensive, organized, straight to the point, more than valid expertise, but what struck me is your enthusiasm and eagerness to convey competence. You deserve a like and a subscription. Thank you for your effort.

[@iliassaek4609]

only with these videos I've aced the design patterns exam . Thank you .

[@madhurajanaradhanan3368]

What exam?

[@zizimouad8291]

People don't understand the hard work puts for +1h explaining design pattern + editing, thank you 👌

[@mayurdugar03]

Can I just take a moment and appreciate your efforts here! You made design pattern really understandable for me! Hats off to your efforts 🙏🤗 Wish you get everything required to be able to continue this series as well. Take care Christopher :)

[@dscheme4427]

36:00 definitions 51:23 code

[@omarabdo6403]

that was a GREAT video! Chris, we're missing your videos on design patterns and different topics really bad! I hope you can find more time in the near future to help us learn more and become better software developers. Much love!

[@MrMikomi]

Watched at 2x speed; it's doable as I've some pre-existing knowledge of this pattern and this video makes a great refresher. Thank you very much.

[@zieldistante]

I really like how you explain things (and sometimes go to other related things and go back). I thought I was the only one who explained things in this way! Thanks a lot for your videos.

[@professorfontanez]

There was a similar example in a textbook I used to teach Java which used three states LOCKED, UNLOCKED, and ROTATING. The transitions were "payment" for LOCKED --> UNLOCKED, "push" for UNLOCKED --> ROTATING, and "one revolution" for ROTATING --> LOCKED.

[@parvez04]

This is a really nice tutorial. Please keep it going. I am kind of addicted to your videos now.

[@FunkyHotDog]

You do a very good job in visualising these problems. Thank you, I'd be in trouble with my design pattern course without you.

[@ChristopherOkhravi]

I’m super glad to hear you feel that you’re learning faster :) I like to think that the quicker we can get the “known things” out of the way, then we can start to think about the “unknown things”. Which imho is where the really interesting issues lie :)

[@JayJay-ki4mi]

I've studied your videos for a while, and come back to them. But, I find it's only when I actually need to use a certain pattern that your videos make sense to me. I need to use the state pattern for game development and this video has been a God send. Thank you so much.

[@nicolafontana2738]

This has been very enlightning! Very well explained with the exact amount of detail, thanks a lot!

[@pra86sat]

I have been searching for Design pattern tutorials online like forever, to find something that can be more relatable to the software systems. But all I ever find are Ice cream, Pizza, Burger examples, which makes no sense what so ever. Thank you so much for all your efforts and making sense. I feel I am a better Software Engineer than I was 1:20 Hrs ago.

[@monikaraut5266]

What a explanation 🙌🙌 guys if you are confused whether to watch or not seeing the video duration, just give it a try. As otherwise you will have to waste double the time while reading articles

[@olenaqwerty7895]

the best patterns explanation I've come across so far

[@oztv_]

you are perfect, i have only a few hours before exam i tried to watch 2x speed but it is still perfect because of body language, fluently speaking, diving into everything with clear explanation. need to say that i am still trying to learn english but i understand whole video. THANK YOU A LOT FOR YOUR EFFORT AND AMAZING JUMP CUTS.

[@johnnguyen1655]

I watched tons of video about DP, your DP playlist make you special among the bests Chris!

[@mdkhxyz]

The way of your teaching is very interesting and helpful. Thanks for your effort.

[@ilnurgazizov2959]

One of the best explanation! Thank you very much!

[@RichardGomezMx]

Amazing explication. I loved it. Congrats Chris. Great video. Thank you very much.

[@BM-jy6cb]

I love this entire series. Fantastic!

[@finyog]

It is a very informative content, presented nicely. I like your videos and the way you explain things. Keep up the good work Chris 👍😊

[@NoOne-pi8cj]

Thank you so much for providing so many awesome videos. Even though I am unable to fully understand or master each every pattern, but you gave me the courage to dive deep into OOD. I will definitely read these two books again. Thank you !!!!

[@ChristopherOkhravi]

I’m glad to hear :) Thanks for commenting!

[@ismailktami2727]

Thank youuuu sooo muchhhhhhh ! your the best way to understand the concrets concepts of DP

[@hdanijel]

Hey man, I just found your channel. Immediately I knew I liked you, and it took me a while to figure it. It's cuz you look like Antonio Banderas! Your energy also is amazing! So much alive and warm :) I'm a smart guy, but as soon as I build a game that has all the basic elements . . .I get lost in the jungle of the code. So I started reading about design patterns. Well, my friend. You're the first one that I can follow! And even understand to that point that I can really see what you drew on your whiteboard as beautiful! Please keep making such simple videos and stop for so many explanations! :) :) :) Thank you man! p.s. Headfirst book sounds like a thing for me Love from Croatia!

[@galtals]

great sound effects. the "boop" sound is to die for.

[@felixjost8206]

Thank you so much for your passionate work!

[@nickeax]

Great teaching and information. Thank you very much!

[@Amine670]

Good explanation of the concepte and theory of the State Design Pattern, when rarely found in KZbin. (y)

[@semajxocliw]

i literally love you for these videos

[@user-ew9qv3zy1y]

Thank you so much for these videos!

[@niclaskron3384]

This was amazing, I learned alot. Thank you Christopher :-)

[@johnmcway6120]

This channel is such a blessing. Thank you so very much Chris.

[@davidsierra3300]

excellent video, you have the gift of teaching! subbed

[@lyonyan]

Only 72 comments? Here one more to appreciate your hard work and effort!

[@orenfarhan8584]

Nice one, but I disagree with passing the gate reference. If the interface for a state declares that an action causes a state to generate a state (e.g return GateState), you can avoid passing references to the gate itself, and from your gate call the action on the state to return a new state, and assign it to your ivar locally. Other than that, I like this playlist. For each pattern, I created a swift playgrounds version for future reference. I wasn't aware I was using so many of them :) Keep up the great work!

[@VictorCarvalhoTavernari]

Hi, Could you if possible share your playgrounds files? I loved your solution about how to create a new State, just returning a State on each function, but if you are doing an async request probably you have to wait this new state, so probably call a delegate like changeState is better for a reactive approach.

[@SemyonKalyakulin]

As I remember, he mentioned that possible solution before the coding part:)

[@amirkhazama7464]

what if the action we wanna do actually does produce a result and returns it like for example the payOk should return the payment id or something ... in that case the return type could not be just the new state .... . . . . . . . maybe you could specify the first returned item to be the new state and the other results to be the other stuff you are expecting from the method ...

[@catcat942]

This was good, I learned alot. Thank you!

[@jojojojo483]

You are a great teacher!

[@alfredoportocarrero8663]

The best explanation of this pattern in the internet still 2020

[@EuanFR]

As suggested in some comments, I would rather return the next state to the gate, from the states "action" methods, something like "nextState = currentState.actionPerformed()" (instead of a void return)

[@abhishekjain3527]

That would be helpful if you are returning void but if you are returning some response then you cannot return state. There should be a signalling mechanism to change state i.e one state should signal the parent gate to change state. And for states there should be a factory that creates these states

[@Wubwub772]

@@abhishekjain3527 ​ you should return the new state and use "signalling mechanisms" for "some response", not the other way around

[@osamucamarques]

Very good stuff. Thanks man!

[@shanm4629]

Once again.. another Great Video . Kudos to you.

[@user-mb6cn8zq4v]

Now it`s all clear, thanks !

[@sarastanway8861]

wonderful series!

[@nikiforovpizza]

Thank you, dude! Useful and comprehensible tutorial)

[@ChristopherOkhravi]

Thanks! Im glad to hear! And thanks for watching :)

[@mfelsheikh]

This is amazing, really great Thank you

[@rohitashkumawat5646]

Best design pattern videos 🙌

[@kalinkalin4543]

last repetition before exam, great job :D thanks

[@ChristopherOkhravi]

Glad to hear it helps :) Best of luck on the exam! :)

[@tomaszb9668]

Really really good tutorial. Greetings from Poland:)

[@chandankumarmishra336]

very nicely explained...thanks a ton for this :)

[@ravisankarjampani213]

Simply Superb

[@aladdinoscopy]

looking fierce bro! Thanks, you explain very well. ….. 25 more minutes in and damn even more impressed. I subscribed, thanks for teaching,

[@TeotoniodeCarvalho]

Very useful and clear even for a soil scientist like me!

[@kattakittaxr]

wow this is an amazing tutorial thanks man

[@edcatmull9253]

Love this, thank you!

[@Generally2310]

Great work 👏

[@spin851]

Great video and channel I like it very well

[@susanmbernard]

Super helpful~Thanks!

[@saurabhmahal1354]

got a deep dive into it .

[@turtla3606]

Amazing! Thanks man!

[@vinokanthvelu2660]

Hey Chris. Thanks for these invaluable content. One request. Could you please do a video on Interpreter design pattern? Thanks mate.

[@DavidBeharL]

I like It a lot, a bit longer than expected, but perfectly understood, this is a pattern very used in React, but this video is very useful to use It better

[@user-ug8qc6tr6b]

brilliant content!

[@ChristopherOkhravi]

Thank you very much. I’m glad you appreciate it 😊

[@loggoggles]

Thanks!

[@MrChezzwizz]

Thank you for your explanation. It was especially useful to hear about state diagrams and to see them used in the explanation of the UML. Your method of repetition seems to really help link your different parts together. I did have one question that I may attempt to experiment with myself and that is why a concrete state object wasn't returned from the action/message handler methods and used to set a reference in the context?

[@miracaknar9549]

I will be your patreon if you start making videos again, you have my word.

[@tofahub]

Your videos are amazing. I enjoyed every bit of them. There is not a lot of good tutorials on advanced OOP on KZbin. Can you please consider making some?

[@bbabak2]

Thanks a ton!

[@GavinKimpson]

I like this video will check your other videos for sure

[@sweetteddy390]

Thank you so much for the wonderful explanation Chris!! Looking forward to more design pattern videos from you... for Builder/FlyWeight/ChainOfResponsibility/Memento/Mediator/Visitor may be? :)

[@meratube007]

Helpful ! thanks

[@campanileLabs]

Thanks alot

[@javieralexandervictoriabal636]

Eres muy grande!!! muchas gracias!!!!

[@kushagr0123]

Thanks a lot.

[@bakyayita]

Much appreciated 👏🏽👏🏽👏🏽👏🏽👏🏽👏🏽👏🏽

[@professorfontanez]

Regardless of mutability, I would not store a Context (Gate) reference on all States. That creates a stronger bind between the Context and the State than simply using the context with needed (and then discard). With this in mind, I would simply pass the Context to each of the State interface methods so that the concrete State could then use the context to set the new (current) state.

[@riteshtyagi5439]

Thank you your gateness

[@avimehenwal]

Wow! this is a jewel :) I would be using state pattern with my upcoming project and this video explains everything on topic. Excellent video. Keep the great work up (Y) I would like to hear your opinions on Inversion of Control and Dependency Inversion principle from SOLID. I am super confused between these two and can seem to make distinction between them. They look same to me

[@ChristopherOkhravi]

Question of the day: Have any examples of where you successfully used the state pattern?

[@MarlyssonSilva]

I think that I've used it in a functionality where I manage a events system where there are subscription of people to participate... and the subscription have state : open, running and closed... where depends on your state some objects will be handled of different ways.

[@lifescience2050]

I developed a POS (point of sale) cashier app using the state pattern, seems the only practical choice. Your video is good and refreshing, our support developers definitely should go through this video before reading the POS code.

[@pascalampere6098]

Used it in a VR app, where the Input of the User needed to cause different things to happen depending on the current state.

[@user-ug8qc6tr6b]

I build simple 2d game on JS. Decide to implement player state via state pattern. State like `idle`, `jumping` etc. By the way game examples is often easer to understand, when you explaining programming concepts. There is one interesting book, which I read recently "game programming patterns", maybe you will like it

[@konradkudzia28]

Games. AI.

[@monkeyrobotsinc.9875]

amazing. you rule!!!!

[@olivermeyer3963]

Hi, many thanks for the video I' ve learned a lot, appreciate that. My question or maybe suggestion, would you consider to change the names, to turn the names of the states e.g. OpenGateState => GateStateOpen, ClosedGateState => GateStateClosed etc. because int this way it's even more clear that they belong together.

[@kareemjeiroudi1964]

I really like the idea that sometimes I don't get it the first, but then he tries to rephrase what he's saying or puts in a different way or with a different example, and then it starts to make sense to me. That's a lot of effort in explaining. He should become a professor or something.

[@ch1l3no]

Really nice job! Subscribing :D

[@lesvideosgaming6910]

Thanks you :)

[@deathangel908]

It's great how you can describe things on the desk, but I guess the coding part can be done in textEditor or smth. With splitscreen so every class would be visible to a viewer at the same moment of time. The code would be much cleaner and readable thus. Means = more understandable

[@pascalampere6098]

Random thought after you read the definition from the book at minute 38: Apart from the reactions to transition messages there could be a lot of other stuff being done differently depending on state. So maybe that is why they wrote that the object will appear to change its class? Obviously, the state needs to be able to deal with all potential incoming messages but apart from that it is pretty free-form regarding its capabilities, right?

[@theisegeberg]

Dang! This is the best of ALL the videos so far! I really thought I just knew this pattern inside out... and still the devil is in the detail... I'm saddened that it doesn't have more views, ALL developers should be forced to watch this :)

[@kareemjeiroudi1964]

I was thinking the same thing. He makes things ten times easier to understand. And I also think that all developers out there must watch this design patterns series.

[@VexingCode]

THANKS!

[@ChristopherOkhravi]

You're very welcome :) Thank you for watching :)

[@kgck15]

Really aweaome way of explaining concepts. More than that tge passion you show is tremendoua. Thanks for sharing uour knowledge. One question i had was ...why is pay part of gate class after paymentbdoes not happen on a gate. Having payok makes sense but not pay. Isnt it?

[@thomastesson9399]

Hi Christopher, great videos and playlist. It helps me a lot to appropriate design patterns. About the State Pattern, it kinda looks like the Strategy Pattern as each state has its own logic, right? I would define the State Pattern as an evoled Strategy Pattern. Do you agree? Do you consider make a new video in this playlist to explain the difference(s) between these two? Thanks again :)

[@noorafshanaz9092]

Wow super ❤

[@Mayukick]

Great video! I have been struggling to understand State Pattern but you made it really clear! I’m not very sure but the sample code you provided seems to be impossible to instantiate (apologies if I’m wrong) The reason is that the Gate class requires GateState object in the constructor while GateState requires Gate object in its constructor. It looks like circular reference, would it be possible to instantiate? (I’m gonna test it out when I’m available)

[@shaileshchotoe]

great content, used to watch your videos years back, and now again. i noticed a small mistake but its not a big detail: in 7:10 u mention that if youre in the openstate and you receive a payOk message you stay in the Openstate, but in 58:11 youre giving an example for when youre in the openstate and you receive a payOk you close the gate. i think you accidently overlooked it

[@MrRicharddaniel]

Hi will this video help someone new to redux understand the redux pattern ? I have been learning react from some time now and just like everyone else, jumping into redux which is confusing me... would the state pattern help ? Thanks for the great videos Christopher :)

[@abhishekjain3527]

Also how does it apply to multithreaded application as each thread could request the gate but since we are changing the state, All the threads has to wait for the processing thread

[@user-po3lq7xc7n]

Hi Christopher, first thanks for making this series. I actually have questions regarding state pattern around 1:11:15. I see that whenever you change state you initiated a new state. I think for the same gate, if it opens, closes, and repeat, it should reuse the existing state. Am I wrong? I don’t understand the potential benefit of countinuous instantiation. Any light shed on my confusion would be appreciated.

[@shakirrasheedkhankhattak9052]

Hi, such a great videos, really great step, salutation for this step. I have a question. Q - What about the GUARDS of the transition? such as events or actions on how to implement it.

[@MichaelKire]

Shakir Rasheed Khan Khattak I know this might be late, but think of code as being coded as the “happy path”. There can never be a false state. So if something happens that isnt allowed to happen, you throw an exception.

[@khaloui3736]

Hi Christopher, first thanks for your explanations it helps a lot. I did not check the other comments, then I will give you my question (4 years later ^_^') Each time a state is changed by a handler by the changeState method. And through this method a new instance of State object is created. So here is the point: how the older state instance is deleted ? I suppose it depends of the languague we use but in some examples, a static instance is used