Liskov's Substitution Principle | SOLID Design Principles (ep 1 part 1)

[@KawsarJami]

I fully understood LSP when you said on 10:57 "they're trying to show us when we should not use Inheritance and when we shouldn't"

[@abdullahbhojani4772]

exactly!

[@linjustek]

So the quote states, that we shouldn't use inheritance :D Or there is an error. :D. LSP is says that we should adhere to method argument and return types, when using implementation or when extending abstract declarations or overrides. Usually when you do not do that, but implement Interface with type declarations you get Type Error. 🙂 And we have to understand that type declaration can be abstract or interface, so child classes can be a fit for as an argument or return type.

[@MrWilde]

I have been watching online training videos for more than 15 years and the you can spot a great teacher when they have as much energy and enthusiasm as you do. Fantastic video

[@NdamuleloNemakh]

So basically it's, "whatever the parent can do, the descendants should be able to do that [and more]"?

[@MilaBarross]

Omg, thanks a lot!

[@lordmorgoth7]

it's, "whatever the parent can do, the descendants should at least be able to do that"

[@karthikeyancseskcet]

@@lordmorgoth7 great words

[@soumavanag5025]

@@lordmorgoth7 golden words

[@ipodtouch470]

Yes but the big caveat is just because the child must do what the parent is able to do does not mean the child has to do it in the same fashion

[@McSeeMo_]

I imagine with the actual viral context you may have spare time to continue this series ! The crowd ask for it!

[@waelsalama84]

Hey Christopher, Hope you're very fine! I got shocked why did you stop this serious.. where are other parts..?? You're awesome teacher and really you've the skill of explain things in a very clear and easy way.. please don't stop producing these kinds of videos. waiting for other parts .. really in a big need to them .. really appreciate your efforts .. Keep it up!

[@SakethSusarla]

unique perspective and wonderful deconstruction, thanks for sharing :) it's 2020, still waiting for part 2...

[@ringoaikocascade]

I am so excited for the part 2. Especially for the past several years I've been avoiding variance, covariance etc and could really use his intuitive explanation.

[@michor10]

Yup, we're all waiting for the rest.

[@jfilipcic]

Still waiting

Is part 2 ever coming? We are all looking forward to it!

[@davidzhou9834]

It's 2022

[@MontagoDK]

part 2 ?

[@bananek131]

+1

[@sebastianvera5830]

+1

[@abderrahimouakki6734]

+1

[@pparturo2007]

+1

[@yevheniisemendiak2501]

+1

[@radu5log76]

Thank you. You have really helped me understand Design Patterns and now SOLID. You are not assuming we know what you're talking about and that really helps get your knowledge across.

[@ChristopherOkhravi]

Thanks! Your comment is super helpful :) Much appreciated :) Thanks for watching and for the feedback :)

[@RocckeFella]

Bro you are doing a really good job. I really love the way you explain things.. more power to you.

[@hana-games]

part 2 to save my life

[@driden1987]

Cristopher!! What will it take to have you create the video about covariance and contravariance ?

[@schmidtlach]

Good and funny. Christopher has a nice way of explaining difficult concepts in simple terms. I loved the video.

[@kinvain]

Wow! It takes you only 16 minutes to explain me Liskov principle and finally I can understand it. You are simply amazing!

[@cehdmoy]

Break Liskov is too easy, that's another reason because we should not use inheritance just for "reuse" code porpuse. Well if you know what are u doing, please feel free to use inheritance. But even Efective Java encurage developer to prefer composition instead of inheritance. My point is when we use inheritance IMHO we are so naive and we think that we can handle it, but finally we get a dog that acts like a airplane (LOL) and we have broken Liskov.

[@alecc8231]

Thank you Roberto. That's quick and easy to understand. If inheriting from dog you end up with an airplane = breaking of the Liskov's substitution principle. Quick and easy to remember. LOL. From now on I'm going to use your explanation.

[@guzideesra4743]

I swear, you should be the Dean of my University. Thank you a lot Mister Bean

[@Vendavalez]

This is one of the best explanations for this principle that I have been able to find out there. For many of them I would walk away feeling like I understood everything that was being said, but not like a I learned something that I could apply, let alone ideas on how to apply it. I would love for this series to be completed if you have the chance or for you to address the topic as part of another series.

[@TheLifeRockss]

2018 almost finished.. still no part 2? you can't do that to us mate :-)... Imagine Game of Thrones not releasing season 8

[@hiteshchalise3988]

now after watching season 8, I wish they didn't released it. lol

[@avnishsinghtomar7783]

we would have lived without season 8.

[@yawar110]

Gist: The subtype MUST be able to do what its base type can do - Excellent clip! Keep posting good stuff.

[@giveexamples]

Learn the most difficult things while your brain stopped and doesn't work with Cristopher's magical videos. Thank you man.

[@StuartLoria]

When I study I vocalize my ideas similar to how Christopher conducts his presentations. I love the demystification of concepts in order to allow more people to get the job done, and enjoy engineering, no reason to be selfish or arrogant, these youtubers are fighting the good fight I think.

[@ChristopherOkhravi]

💛💛

[@jg5645]

Chris

[@a.rohimsama7222]

Yeah, the same here I like him.

[@vunguyenhoang3704]

really hope to see the next part. You are amazing broo

[@shaimaaaltaay5183]

OMG thank you so much I have an exam on Wednesday and I was lost with LSP principle.... I never enjoyed a lesson this much before thank you again

[@ChristopherOkhravi]

Aha. Great stuff :) How convenient :) :) Best of luck on the exam! 👍👍

[@shaimaaaltaay5183]

Christopher Okhravi I explained LSP to my friends before exam and they were like “oh that’s it 😮 it’s so easy” and I was like “yeah can you imagine “ and then gave them the link to your KZbin channel 😁 BTW DIP came in the exam not LSP 😂 except that scenario question with classes and DIP example I think I did well

[@ooredroxoo]

The funny thing is that you had a video on Liskov Substitution Principle posted on July 2016, that was the video that made me discovery your channel.

[@ChristopherOkhravi]

Haha :) Awesome! Super thanks for sticking around :D :D

[@salmanahmedkhan3979]

Preparing for exam and this masterpiece is pop up. Great Explanation

[@janabodu3392]

Mr Bean mastered design principles and became Christopher Okhravi...Great Explanation ...Thank you..

[@ЕдвардГригорян-н6к]

the best explanation pf lsp. Please return to make these videos. You are one of the best teacher on youtube

[@RamKumar-kv1fx]

I though I knew Liskov's Substitution Principle for around a year but its only today I understand it correctly. Thank you very much Christopher Okhravi

[@sunilphanimanne]

Hey @christopher okhravi, I dont think 0(phi) need not be on the type T and the subtype S, what is being said (from my understanding) is - If there exists a property (on some arbitrary class or type) which takes T as an input then the same property should work even if invoked with the subtypes of T i.e S here. I hope you agree with me.

[@sunilphanimanne]

... and to add to that, the 0(phi) can be present in T and S, there is nothing wrong in it though!

[@rupn9633]

Very Unique way of explanation, I have see many videos on SOLID principles , this one standout. Great!!!

[@LucidFabrics]

Any chance that you could do a continuation for that video ? Many thanks!

[@zbigniewcwiakalski7253]

Ech. That would be super cool to hear more about this in the next episode .... Hope it's going to be created eventually ;) regards

[@MultiPauwel]

Top Notch explanation, i'm not a native english speaker and i followed some guides on PluralSight, came here because i still didn't get. Now i heared u talking, it's darn simpel, once u get it! Thanks alot!

[@nitendratiwari3709]

Hi Chris, really nice explanation, but you know best part @ 5:36 which my daughter of 3.5 years Liked a Lot, She didn't understand the principle but she likes ur expression a lot ...!!!, Thanks

[@jctkc]

You are the best man!! I've watched all your videos about Design Patterns and now I'm watching this and your explanation is simply great!. Thanks a lot!

[@shubhankarpaul2740]

10:08 is what you have been looking for .... EXCELLENT !!!

[@tsvetanpetrov5971]

Amazing! Usually, this is one of the hardest questions during interviews. Thank you for the hard work!

[@rohitkalya]

Hi Chrisopher, Can you please post the 2nd part of this video.

[@mufizshaikh8439]

It was very easy to understand with the help of your video. Thank you

[@Erdling123]

Not only a great explanation, this was entertaining as well.

[@ronironion]

Awesome man! So easily served!

[@iamyajivhere]

anybody has the link for part-2?

[@cetiah]

I just recently learned from one of your videos that the snail would speak, but it would have a NullSpeaking behavior that's returned when you run Speak() on the snail.

[@toooldtobejunior]

I think the only way to violate LSP is using "override" keyword for a method. Therefore if I did not use "override" I'm safe. Do you think it is correct?

[@ChristopherOkhravi]

Good point. Very interesting. I’m not sure actually. I’m suspecting there’s some further complications around generics (i.e. parametric polymorphism, think T in C#) but I need to learn more before I can have an opinion about this :/ Sorry! But thank you very much for watching the video and dropping a comment!

[@toooldtobejunior]

@@ChristopherOkhravi Thank you for making these videos. I absolutely love them.

[@saurabhshukla4900]

This video has useful content worth just 2 mins.

[@slobom.6744]

The force is with you, all Jedis should be ashamed of themselves! :)

[@cepi24]

Sir you are doing great job and seems you are enjoying it

[@divyeshkumarbalar7732]

its been 4 years since i commented, still waiting for part 2 :)

[@opsherx]

this guy is so excited hahah thank you man

[@aymanshaawat]

I really hope that you continue this series. Or at least start a new one talking about the same topic.

[@JaspreetChhabra]

One of the best explanations...

[@naito016]

2020 year, after a lot of videos listening blah blah and blah about Liskov's Substitution, finally understand the Liskov Substitution Principle then I Think this video was awesome need the next one, it's pretty weird that KZbin is not showing part two on following video, go to authors channel, looking for the part two that never comes.

[@aprendemusica1931]

Love his passion teaching 💞

[@gourangabhattacherjee6648]

where are the other video of this playlist?

[@shiblimohammadarafat6602]

It's indeed a great lecture! I have been trying to understand Liskov's Substitution Principle for a long time. Obviously I had some understandings which is correct but I also had some confusions as well. But your explanation is so clear that now I don't have any confusion about it. Thank you so much.

[@danielmilewski7659]

cannot wait for part 2 !!!!

[@sunnyshekhar862]

Just discovered your channel... And my my, What a fine job you have done explaining these concepts. I am from a non-Computer Science Background and even I was able to understand the logic in one go !! Seems like it's been more than an year that you did the 1st episode... Not sure why you dropped the Series... but like me many would love to see the 2nd and subsequent episodes in this series. 😇

[@tomaszb9668]

i can't find part 2 of liskov's substitution

[@jeffdosser4251]

Your vids are great. More ppl should be watching them.

[@divyeshkumarbalar7732]

Where is second part?

[@Name-lt2tz]

12:02 - if S inherits from T, how it can not have T methods? It is not possible, at least in PHP. Also I do not understand why you call methods as properties? For me property sounds like class variable. This was confusing. Or maybe this principle means that you cannot have empty methods. Like if there is parent class called Animal and has method speak. And we create Snail which extends Animal, and automatically snail has method speak() but we make it empty, or it is empty in Animal class - then maybe this is bad?

[@c4stus]

Great as always Christopher, love your videos and your way of explaining stuff, don't stop please :)

[@davidecullen1]

Thank you! You helped me understand this principle the day before an interview!!

[@felipeignaciocastrojara5065]

THANKS bro, love from Chile!

[@taskapptaskapp3138]

You are great man. You should have more views. I wish you all the best, greetings from Poland. :)

[@tusherkhan7531]

Thanks for making it easy!

[@michaelhaddad2190]

Thank's a lot! I thought it's hard to imagine how we could possibly break this principle, until one day I tried to add an instant messages feature to my program, and I created a "Participant" class, which inherited from "User". Then I realized that although a "Participant" IS A "User", I could not substitute "user" with "participant" anywhere in the program, and if by accident I do it in the wrong place, things will get really bad. That is when I realized that inheritance actually doesn't represent an "IS A" relationship, but rather an "IS A SPECIFICATION OF" relationship.

[@ChristopherOkhravi]

This is a great example! Thank you very much for sharing!! :) :) Super helpful! But when you said “specification”, did you actually mean “specialization” rather than “specification”? Or, if the latter, could you please elaborate? Thanks again! :) :)

[@michaelhaddad2190]

Thanks! I did mean "specialization". Sorry... My English is not great :P

[@bryancorea678]

Please continue this amazing videos

[@AdrianBlogs]

I like your way of speaking you also speak English very well and I understand what you say

[@rubenbasketpalencia]

You can also talk about he exception throwing. A subclass mustn't throw an exception that it superclass can not throw. (correct me if I am wrong) Thanks for your videos!

[@mevadavatsal]

Thanks for the in-depth explanation. BTW @ 7:06 : the symbol is "Phi": en.wikipedia.org/wiki/Phi

[@harishnamjoshi]

Chris you are a savior. Just love you videos. Waiting for next episode. 👍

[@irgatyus3090]

Thanks a lot man for your visionary approach. I'm about to get my dream job thanks to your educational channel. Keep up the good work.

[@ChristopherOkhravi]

Wow! Thats cool! Congratulations for the new job! 🙂🙂

[@stekl.h]

Lovely lesson! Thanks

[@mrinaldhawan3959]

Great videos man! Complete this series. I have already watched the Code Walks of SOLID. This came to my mind while watching this video. Not sure if this is a correct analogy! At 14:17 when Chris holds the RED and GREEN Markers on screen, We believe that GREEN is Subtype of RED. Lets suppose the Marker Caps are properties of the Markers. If we remove the Cap from RED and replace it with GREEN marker cap, it should fit perfectly as GREEN is truly subtype of RED.

[@amirbeheshti9010]

If you state something is true about the PARENT type, It HAS to be true all the way down the chain ... Neat👌

[@abdelaziz2788]

pleaseeee continue the playlist u make it so simple

[@firstlast1947]

One thing I never understood about Liskov Substitution Principle is why it exists? I thought a core part of Object Oriented programming is that if you have a reference to a base class, it can refer to an instance of the base class or any derived class, since all of the derived classes "IS-A" base class. Or is Liskov the person who came up with that principle in Object Oriented programming, and that's why it is named after her? Otherwise, why give a name to something that was already a part of Object Oriented programming to begin with? It would be like someone deciding to name addition the "Bubba Joe adding principle", when addition already existed before Bubba Joe came along to give addition his name.

[@gunarsekaran]

I watch many videos to understand about LSP, Finally i am got my inner peace🍻

[@seres3694]

hi, how do you read ϕ i have been searching for a while but i cant find how let x have a circle property be a property let x have a property be a property let instance of x be a property i got confused, can you help me out with the correct word.

[@andersonchica7110]

Are you going to explain the others principles?

[@0xlilx0]

Great explanation! Been reading about it for an hour and nothing made sense, but your video made it clear :)

[@binhhq89]

I can't find part2 of video

[@misetro12345]

Christopher would like a part 2 for this video

[@suhas002]

Great work man .. you are making things easy to understand.. waiting for other principles ..

[@talldutchguyk8247]

Where is part 2?!?!!?!

[@saurabhsuman4960]

You are amazing. I love the way you explain. 👌

[@asharnavya]

I am waiting for you next part of this series. When you are going to post ?

[@the_unico]

Never knew Mr. Bean / Rowan Atkinson is a programmer. Great Content bro

[@Name-lt2tz]

where are those other videos about liskov substitution principle, which you mentioned?

[@georgebockari289]

I'd really love to see you pick this back up.

[@ossamabounnite4922]

Thank you for the explanation, Christopher. But, what I don't understand is, this principle is always true in Object-Oriented Programming where a type can be always substitutable by its subtype. Can you, please, provide some examples where this principle is violated. Thx again!!

[@kevinbenavides92]

Thank you Chris. Please continue this series on the SOLID principle if possible. Your the best.

[@ChristopherOkhravi]

Thanks! Will do :) Thanks for watching :)

[@UrzaRage778]

You're fantastic at explaining things! (Much like Tim Corey) - where'd you go?!

[@IlyaShap]

Wow! You’re an awesome teacher. Thank you so much!

[@Name-lt2tz]

Also question - if we want Snail to not have method speak, but snail is still animal, then maybe we just remove speak method from the Animal class. And maybe create some class SpeakingAnimal which has speak mehtod() which extends Animal. And since Animal will not have speak() method, we can make Snail extend Animal.

[@yogini1351]

Hello Christoph, You are awesome. I think I have watched almost all of your sessions on design patterns. This one is also amazing and simplified, but I didn't find the part 2 in this playlist. Could you please help with quick link?

[@pawekrzyzak4345]

I have still waited for the next one!

[@soufrk]

Really makes it's simpler to understand !! Way to go

[@ChristopherOkhravi]

Thanks! I’m glad to hear :)

[@B-Billy]

Woow... That was awesome Please keep it up.. Great job And yeah, thanks for sharing. BTW, I missed that cat 🐈 LOL

[@abhilashbandi3866]

Thanks for this :) I believe understanding SOLID will help in understanding Design patterns a lot better.

[@ChristopherOkhravi]

Thanks! I’m glad to hear :) It’s all connected indeed! :)