This is the first LLD video where I saw real coding example.. and not just theory. Great work man!! Keep it up !!

at 32:41 , the reason for not notifying again is that, in the implementation of obj.setStockCount(newStockCount) { stockCount = stockCount + newStockCount } not { stockCount = newStockCount }

As a fresher , Started learning LLD from today. Enjoying the concept .so simple explanation and easy to understand Thanks bhaiya

For the notify function in observable concrete class, we can call the update of observer and send the current object in parameter. In the observer class, we don't necessarily have to use instance of operator in conditionals, if getData() is there in the observable interface, then we can directly use observable.getData() and it is fine. No need for constructor injection as well

Recently i started reading Head First II edition, I come back to your examples after going through each chapter. Thanks a lot for knowledge. It's really helpful.

Just brilliant, You are giving us true insight into enterprise level coding,, thanks a lot

Happy to be here before this channel blows up. Keep up the quality content.

bought Gaurav Sen's course but you explain better than him. I saw only 1 video from his playlist and will watch all ur videos. Keep up bro..

Hi Guys, how was the explanation? Please let me know where i can improve. like voice speed and clarity, depth of topic detail, handwriting, example taken etc.

Very nice explaination. In the Observable concrete class, you should first update the stocks value and then call update for the observers. Reason: It might happen that the update method in Observer has something to do with the number of stocks currently available. It will get the old value not the updated one.

Simple and brilliant explanation. Particularly good for those who is revising and have some idea

Hi Shrayansh, Your amazing man, I have reviewed Java and DP's. Now i am fan of you. you make concept simple, understandable and moreover easy to remember, Thanks for your hard work man. you have great future. For sure we see more video's going forward.

I think that in the setStockCount() method, we should do stockCount = newStockAdded instead of stockCount+=newStockAdded since let's say we want to make the stock as 0 as in 32:42, the stockCount will stay 10 itself as 10+0 = 10. That's the reason why it didn't notify second time. Please correct me if I am mistaken somewhere while understanding this. Thanks.

An Observer can register with multiple Observables. If we use constructor injection, then we are limited to only one Observable implementation which is usually not the case.

just joined the channel for lld, hld and java videos, great content bro, worth the money 😃

Thank you @Shreyansh ! I have never found a better Design pattern video.

nicely explained Shrayansh. Hope to get more videos on LLD.

Hats off to your explanation buddy.... big fan of your teaching 😊

Too good.... This level of depth in knowledge covered with such simplicity..... Its phenomenal. Thank you so much and keep the good work up

Man! You are really killing in teaching the concepts❤️.

One of the best explanation on youtube. Thanks

Amazing simple explanation i have never seen such a simple explanation keep it up 😊

observal -> state changes. observer -> state changes of observable observed by observer make there interface where there can be many observer but single observable and make there classes In observable class u will make a list of observer , u will add observer, remove objserver , notify all observer , and change the state of data or get the state of data.

the best teacher for lld

Thankyou for this video. The mixture of the question and the explanation pattern together, will help me to remember this kind of scenario well. Thankyou once again!

Simple and crispy explanation, hats-off to you

Why i found your video so late ?Anyway, You make things easier then what people used to complex it.

Very good explanation with examples, Thanks a lot for such videos.

Loved the real-time scenario

Very Nice Explanation. Please keep on adding new videos on these topics

Well explained, you gave a good clarity of the concept, easy to remember + revise.

Hi Shrayansh, wouldn't there be need of initializing many objects if there are many obervable for a single observer...dependency injection in method update will be better right? THen both of them become loosely coupled, and anyway since the method are from interface we can call it using the interface argument......eg could be like 1 user can call notify on multiple items..so in that case it becomes m:n relation.. pls correct me if i am missing something

can you give another example where the observer has multiple observable? In this case i think instead of having a observable object inside the observer , we might need to have concrete objects as task that the observer will perform after geting the data from the observable(s) might depend on the type of the observable. For example: if the observable is temperature increase , the observer will lower the temperature , and if another observable is item in stock notification , the observer will place a order for that item. Or if we follow what you said in this video , where i dont have to check the type of observable , then i might need to make differnt types of observer Example : TempObserver, StockObserver

Great explanation man! It was really helpful

Question 1 : In case of more then one observable in a single observer, wouldn't you still have to check which observable called the update method? resulting in some if/else again inside update(). Question 2 : If we don't send the data in update(), won't the update logic loose on some data in case of race condition? (say temperature updates few times in a row, and since instead of passing the temperature value we are passing observable object which will have updated data always.)

Buddy it's easy to add caption for old videos. Just edit your video in KZfaq studio and select English in caption drop-down and then click save/submit changes. It will take sometimes to add caption automatically to your video.

Bhai kya explain krte ho yr, maja aa gya. I love you.

Nicely explained everything ❤

Again very well explained , And yes it will be nice if you explain Implementation With PropertyChangeListener which is another way to implement this.

Thank you for the detailed video. Very good explaination.

Hi Shrayansh, thanku for this amazing tutorial.

Why can't you pass 'this' (instance of WSObservable) in the update instead of constructor injection. You can then call whatever methods on that like you did with constructor instantiated object.

While notifying observers, we should do the same in an asynchronous manner.

Greate work, Huge respect for you bro.

Awesome Explanation♥

Bahoot hi achha explanation

Very crisp and clear explanation.

🎉🎉🎉 perfect explaination

It was good ..one suggestion .. Koi ek hi language me poora video banaiye ..Kabhi kabhi aap english me switch ho jate ho ..HIndi me hi rakhiye

Good stuff Shrayansh. Keep them coming

excellent work man, this is really good, telling theoretically is one thing, but writing actual code is another thing. But i have a doubt, could you suggest anything to C++ people, because syntax may differ and its difficult.

Great one!! I could not understand the part where it was mentioned that we would have had to use "instanceof" if we were not doing constructor injection. Please add some clarity on that part. Some example would be great!!

Thanks for the wonderful explanation

Sir sach bolu Maja aagaya ❤❤❤❤

Perfect , to the point explanation. Keep posting vedios👏

Sir I am just starting to watching your video. Please Sir make more it'll help us

Very well explained...awsome!!!

we should use set to store all the observers in the observable class

Amazing video, Thank you!

Awesome Explanation ...

Thanks for the video!! Having both Setdata Getdata methods inside Observable class seem to violate Single responsibility principle. Now this class is responsible for both notifying as well as managing the data. May be better to seperate the data managing part to seperate interface and take it as input to observable class

I think thats the perfect example of how a High Level design model such as pub-sub is translated into a low level Observer pattern, I think for each hld there must exisits some corresponding lld pattern that's my hypothesis 😬

Thanks Shrayahsh for this video. In case of multiple customers registering for 1000 products on Amazon, I believe we will not create multiple observers for each product right. How can we accommodate this requirement? How will it work in case of Distributed setup where entire scenario is handled by different microservices. We need a distributed Notification mechanism, right? I believe pubs/subs or event messages may be good option here.

very good explanation. Thank you

Your videos are awesome. But I would like to know the below things 1. which one we should start first hld or lld? 2. In what way we should learn hld and lld? 3. How to practice these and gain hands on experiene? 4. Is it necessary to take a course after watching your videos? 5. Any order, you would reccomment to follow? Please clear my doubts Shreyansh.

very nicely explained.Keep it up

great explanation, thank you so much for making this kind of video.

You explained very well, thanks for your content. just one thing can I get code repo to go through it. or can I download it from somewhere?

In case of multiple observables, do you end up writing different update methods in the observer class. Checking instance of gets replaced with new method strongly tied to one of the observable. Am I missing something here?

Great Explanation

excellent explanation!

Interviewer : Now scale it for multiple products

Hey, Shreyansh, nicely explained, but I do have one question. Q1. we are designing this notify me service for amazon, amazon has lot of products, will each product be creating one concrete observable? or there will be single observable that keeps the record of subscribers for all the product in the form of map of arrays where key is product id and array is list of subscribers and when writing notify it will take product id and notify the respective subscriber. Q2. we are saying concrete observer will have instance of concreate observable, what to do, if I want to observe multiple products from Amazon?

in the update method firstly the count should be set and then if (count != 0) notifySubscribers can be called.

Hey Shrayansh Can you please provide access to the notes and code used in the video? Keep up the great work!!

Great explanation 👍🏻

It definitely helps if this is taught in English. who doesn't know Hindi

Good Video. Thanks man.

Awesome Content

Great video

We can take List in the WSObservable Interface as whenever we will be adding data from our concrete class we can add object to final list as we are not reassaigning new list object but only afding object to final list

Great work man..

very nice

I understand the observer pattern but what if the application goes down or somehow we lost the stored information(observers) ? in this scenerio how will get the data back ? of course we need to store these information in db. but if it`s in the db then what is the purpose of observer pattern ? we can simple query the db and do the stuff (querying again and again is not good approach ) so can you or anyone explain this to get better understanding about this.

Amazing explanation. nice video

In the concrete observer, we inject concrete observable in the constructor so that we can get the updated state from this concrete observable when a notification comes. But I also think the concrete observer needs that observable to subscribe (register) itself. Right?

Second wale case if we do setStock(100) then it adds to previous count of 10 hence we are not seeing it twice

Shouldn't we have a single observable class which can handle multiple products identified by their ID? Then we can pass this object to the observer and observer will check if it is not null then it can perform some action, so no need of contructor injection also. Please correct me if i am wrong.

1. Can we consider Linkedin Job alert feature as Observer Design Pattern,? 2. Can we get code repository link for all these design patterns, would be helpfull for revision?

Really Helpful!

Very informative video! I have a question that suppose if my store has 100 products apart from iPhone. I would have to create 100 concrete classes for it?

If we keep an instance of Observable in Observer then I can call setData also. It's better to use a Notification object and pass it to the update method. This Notification object will contain all the necessary information.

In the example, I can see that there is a dependency of Observer interface in Observable interface and vice versa. I don't understand one thing how the dependency will get resolved? Will it end up in cyclic dependency? Can you please help explaining it? Which object will get created first and how?

a doubt here , can't this be solved by the following strategy : 1. Use a single table with a composite key (product_id, user_id) to store user subscriptions.The users will be added to based on the endpoint for notify users. 2. When stock becomes available, a Kafka event is triggered. 3. A dedicated service consumes Kafka events and queries the centralized table for users subscribed to the specific product. 4. Users are then notified based on a separate endpoint. Doesnt this eliminates the need for observer pattern here

For a observer having multiple obervers: List observableList, in update method how do we find which data in observer to be updated / what action to be performed ?

Hey I have a doubt here: if we are creating iphone object and passing it in the constructor of observer i.e - email or mobileAlert. then still it is not becoming that dynamic like in a system of 1000 products do we need to create 1000 objects of each product and then pass it in the observer constructor. Need to know how we can make it dynamic when the system is large or there are multiple products.

very good

Hey, lets say if there is a observer concrete class listening to 3 different observables, [video time : 12:55] 1. How will we inject 3 different objects of observables [for eg if a single customer says notify me for 3 different products at different times] in the observers class ? 2. Even if we can lets says we maintain a List in Observer, we still would need to go through all of them to know which one has actually changed. So how is Observer keeping an object / list of Observable/ Observables helping ? Basically whats the best solution in that case ?

Hindi me zaada ache se samjh me aata hai humlog zaada ache se connect kar paate hai

Wouldn’t it be better if you just pass the data directly from Observable as parameter to the update method of Observer? Cause having the object of Observable in a Observer is unnecessary I think. Wouldn’t having so also expose all the other methods (like add, remove, setData, etc) of the Observable to the Observer?