[CS Technical Interview 6] Java and Object-Oriented Programming Made Clear

💬 Getting a developer job - coding tests weren't the end of it.

As someone from a non-computer science background, when I first prepared for a developerjob, I focused solely on algorithms and coding tests. I gained some confidence and passed most coding tests. However, I kept failing at the next hurdle - technical interviews.
What was the problem? It was the lack of CS (Computer Science) knowledge. In interviews, CS fundamentals were considered much more important than algorithms.

🗣 For actual interviews, 'speaking practice' was important.

Even after filling in my CS fundamentals, interviews weren't easy. In an interview at a certain company, I was asked about floating-point numbers. It was content I thought I had read and understood multiple times in books, but I couldn't utter a single word. I painfully realized that passive learning through simply reading and understanding wasn't enough to answer questions in actual interviews.

To succeed in interviews, you need not only to accumulate a lot of knowledge but also the ability to explain this knowledge. This 'ability to explain' can only be developed through practicing to organize concepts in just a few sentences and articulate them verbally. Through this process, you can also discover what you didn't know precisely. Without sufficient practice, you'll encounter the following problems.

1. Conceptual Confusion Type

❓InterviewerWhat are the characteristics of object-oriented programming?
💬 Candidate The SOLID principles. First, S is..(omitted)...

This is a case of confusing similar concepts.
SOLID is an OOP design principle, and the characteristics of object-oriented programming are abstraction, encapsulation, inheritance, and polymorphism.
The moment you mix up related concepts, the interviewer judges that 'your fundamentals are shaky'.
It's not just a simple mistake, but rather it's read as a signal that your conceptual framework is not solidly established.

2. Lack of Specificity Type

❓Interviewer What are the characteristics of TCP?
💬 Candidate It's a protocol that guarantees reliability.
❓ Interviewer What are the mechanisms that guarantee reliability?
💬 Candidate Uh... well... it makes transmission secure... like that...

This is a case where you only know the What, but are missing the How/Why.
You only know the superficial answers and aren't prepared to explain the underlying principles.
TCP establishes communication through connection (3-way handshake), ensures reliability through RDT (sequence numbers, ACK, retransmission, etc.), and maintains quality through flow control and congestion control.
These concepts should be connected as one cohesive flow in your mind. Without organizing concepts concretely, you cannot prepare for follow-up questions.

3. Getting tongue-tied with basic questions

❓Interviewer What is HTTP?
💬 Candidate Um... it's for sending and receiving data on the web... something like that...?

It's such a familiar concept, but when asked to explain it in one sentence, the words don't come easily.
Words like request, response, server, and client come to mind, but they don't flow naturally into a coherent sentence.
This is because we've never practiced explaining from definition to principles in one continuous flow.
This isn't a lack of knowledge, but an absence of structure.

Just knowing is not enough. It only becomes true skill when you can express it in words.

🔥 So I created it. The CS Technical Interview Series That Gets You Talking!

🎯 Recommended for these people

⚡ Lecture Core Kick

💡 Use it like this

💬 Q. The lecture time is short, but will I be able to learn properly?

🖐 Hello! Let me introduce myself! 🙇

I created this course thinking of my past self who stayed up all night worrying about fundamentals and felt anxious over every single interview question.

I started as a non-CS major and understand better than anyone the thirst for fundamentals (CS knowledge, programming languages, etc.). Through self-studying countless materials and building my own know-how, I eventually graduated from Seoul National University and now work as a 🧑🏻‍💻 Kakao developer.

From a young age, I was more confident than anyone in combining and restructuring various materials to create my own 'comprehensive study notes.' This course is precisely that 'ultimate self-study know-how' and a secret notebook born from all my passion and philosophy.

🔥 What makes this course special?

• All of my 'know-how' is included: As a non-CS major, I have fully incorporated my experience and know-how of self-studying CS and programming languages and getting hired at a large corporation. I have included in this course all the methods for how to most efficiently understand complex and abstract concepts and make them your own.

• 'Fundamentals' are key in any development field: Whether you're aiming for game development, AI, web/app development, or any other field, basic computer science knowledge is not optional but essential. This course helps you become a true expert based on solid fundamentals.

• We compete with 'overwhelming quality': I've referenced countless materials including textbooks, famous university lectures, commercial books, and technical interview resources to extract core keywords and reconstruct them in my own unique way. With intuitive diagrams and illustrations, combined with easy explanations infused with my practical experience, I promise to make even complex concepts click with that "Ah, now I get it!" moment.

🚀 Introducing the sixth lecture [Java and Object-Oriented Programming] from the Technical Interview Master Roadmap.

📕 Java is the most widely used programming language worldwide and a representative implementation language of object-oriented design.

• Do you know about classes and interfaces, but get confused about when to use which one❓

• Do you know the concepts of JVM and Garbage Collection (GC), but can you explain how they actually work❓

• Have you heard of multithreading and synchronization, but find it daunting to answer in just one or two sentences during interviews❓

This course is the one solution that will quench that thirst of yours.
Rather than simply listing grammar, it organizes Java's core concepts in a diagram-centered, principle-centered, practice-centered approach,
helping you transform into someone who truly knows.

🎯 Through this course, you will be able to clearly answer the following questions.

• What is Object-Oriented Programming (OOP) and why is it important?
  → Explains the principles of abstraction, inheritance, polymorphism, and encapsulation along with SOLID design principles using Java code examples

• How does the JVM operate structurally, and how does GC manage memory?
  → Organizes class loader, execution engine, heap/stack memory structure, and major GC algorithms in flowcharts

• How do you implement multithreading, and why is synchronization necessary?
  → Shows the usage of Thread, Runnable, synchronized, and volatile keywords and concurrency control methods through practical examples

• What are the modern Java features introduced after Java 8?
  → We compare and organize the concepts and use cases of lambda expressions, functional interfaces, and Stream API

  
  

  
  

📌 At the end of the course, a practical interview practice chapter awaits you.

You can practice answering by yourself in one or two sentences to common technical interview questions like "What are the core principles of OOP?", "Why is GC necessary?", and "When is volatile needed in a multithreaded environment?"

📖 A curriculum packed with only the essentials

Here are the table of contents and key keywords you will learn in this course.

If there are any unfamiliar keywords, make sure to grasp them thoroughly this time.

✏ Here's what you'll learn

👀 Course Preview

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💡 Curious about other interview preparation courses? Check out the roadmap below :)

Pre-enrollment Reference Information