Top 20 System Design Interview Questions for Java Programmers

System design questions are an important part of programming job interviews and if you want to do well, you must prepare this topic. In the past, when I shared my list of programming interview questions, I have shared a couple of System design questions but my readers kept asking me for more questions, as it is a hard topic to master and more and more practice is needed. I had my own list of questions which I have collected from various interviews with friends and colleagues but I needed more questions for this article and my own preparation then I stumbled upon Grokking System Design Interview course. It's an excellent resource because it not only gives you a lot of System design question but also provide all the knowledge and tools you need to solve those questions.

In other words, this course teaches you to step by step how to proceed with designing a real-world system like Facebook, Twitter, Uber etc.

When you combine this course with this list of questions you would have the best material to prepare for your System design interview. You can also first try all these questions by yourself before joining the course or looking it my solution for some of the questions.

System Design Interview Questions for Programmers

Without any further ado, here is the list of some of the most popular System design or Object-oriented analysis and design questions to crack any programming job interview.

1. How to design Vending Machine in Java? (solution)
You need to write code to implement a Vending machine which has a bunch of products e.g. chocolates, candy, cold-drink and accept some coins e.g. Nickle, Dime, Quarter, Cent etc. Make sure you insert a coin, get a product back and get your chance back. Also, write the Unit test to demonstrate that these common use cases work.  If you get stuck you can read my two-part articles (part1 and part 2) about solving this classical system design questions.

2. How to design URL Shortening service like
This one is another common System design questions. You have given a (typically) long URL, how would how would you design service that would generate a shorter and unique alias for it? If you are not familiar with URL shortener service have a look at some of the popular ones e.g. from Google and which is used by Twitter.

Make sure to provide database schema and rationale behind some design decisions e.g. how long you keep the data, how to get stats and analytics etc. If you get stuck, you can follow the solution given on System Design Interviews: Grokking the System Design Interview.

3. How to design a traffic control system?
A classical system design question from old age which is still popular. Make sure you know how to transition from one state to other e.g. RED to GREEN and from GREEN to ORANGE to RED etc.

4. How to design a limit order book?
A limit order book is used in stock exchanges to match a buy order with a sell order based on price and time priority. How would you go about that? Which data structure you will use? Remember, the speed of matching is key and also the reliability. If you need a refresher on Data Structure then you can check out Data Structure and Algorithm in Java course and If you feel stuck you can check out my solution here.

5. How to design a website like Pastebin?
Pastebin allows you to paste text or code and then share a link to that code to anywhere you want. It's not an online code editor but you can use this to store any kind of text.

6. How would you create your own Instagram?
Instagram is a photosharing application which provides some custom filters to enhance your photo quality.

7. How to design a global file sharing and storage apps like Google Drive or Dropbox?
These are used to store and share files, photos and other media. How do you go about designing things like allowing users to upload/view/search/share files or photos? track permissions for file sharing, and allow multiple users to edit the same document?

8. How to design a chat application like WhatsApp or Facebook Messenger?
You have surely used WhatsApp and Facebook, right? No? If not let me tell you that a chat application allows you to send messages to your friend. It's point to point connection. You keep a friend list and see their status and chat them. In WhatsApp, you can also connect groups but that is for advanced and experienced developers. At a minimum, you should provide design to keep friend list and send and receive messages from them.

9. How to design a Twitter Clone?
Twitter is a popular messaging service lets you broadcast your messages to all your followers. You tweet and your followers see those messages, they can like or retweet. Make sure you implement common features like followers, hashtag, tweet, delete etc. If you feel not going anywhere and stuck, you can follow the solution on System Design Interviews: Grokking the System Design Interview.

How to design a twitter clone

10. How to design a global video streaming service e.g. YouTube or NetFlix?While designing a video streaming service like NetFlix or YouTube key thing is smooth streaming and buffering and functioning over low bandwidth connection, how do you manage those challenges.

11. How to design an ATM machine?
An ATM machine allows a user to deposit and withdraw cash. It also allows a user to see his balance. How do you design such system? What are your main challenges?

12. How to design an API Rate Limiter?

13. How to design Twitter Search?

14. How to design a Web Crawler like Google?
A Web Crawler goes to a website and crawl all link and index them e.g. Google so that they can later appear in a search result. A Crawler can also use for searching a particular file in a set of directories, how do you design such things? What are main challenges?

15. How to design Facebook’s Newsfeed? What kind of Algorithm will you use?
The newsfeed is an important part of Facebook which allows a user to see what's happening around his world which includes friends and families, the pages he has liked, the group he has followed and of-course the Facebook Ads.

The job of Newsfeed algorithm is to show messages which is most important for the user and which can generate high engagement. Obviously, messages from friends and family should take priority.   If you feel not going anywhere and stuck, you can follow the solution on System Design Interviews: Grokking the System Design Interview.

Top 20 System Design Interview Questions for Java Programmers

16. How to design Yelp or Nearby Friends?

17. How to design a global ride-hailing service e.g. Uber, Grab, or Ola backend?
Uber and Ola are two of the most popular ride-hailing services, it brings both drivers and passengers together. How do you go about designing to allow a passenger to see nearby taxis and book them?

18. How to design BookMyShow?
A website which allows you to book cinema and event ticket

19. How to design a social network + message board service sites like Quora, Reddit, or HackerNews?
Reddit, Quora, and HackerNews are some of the most popular social network sites where users can post questions or share links. Other users can answer questions or comment on the shared links.

20. How do you design an application like Airbnb?
It allows some users to upload rooms for rent and other users to rent them. Some of the features are only available to admins, publishers, and subscribers.

That's all about some of the frequently asked System Design Interview Questions for Java Programmers. Btw, these questions are not just useful for Java Programmers but also for Python, C++, and Ruby Programmers. These questions are actually independent of programming language and test your software design and architecture skill.

Further Reading
The Coding Interview Bootcamp: Algorithms + Data Structures
Cracking the Code Interview - 189 Problems with Solutions
20 Software Design and Design patterns Interview Questions
Software Engineer Interview Unleashed by Udemy
The System Design Primer on Github
System Design Interviews: Grokking the System Design Interview

Thanks for reading this article so far, if you like these System Design Interview Questions then please share with your friends and colleagues. If you have any feedback or question then please drop a comment.

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