[CS Technical Interview 6] Java and Object-Oriented Programming That Makes Sense

🥲 Getting a developer job, coding tests weren't the end of it.

As a non-major, when I first prepared for developer employment, I was obsessed only with 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 were still not 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. That's when I realized it. Passive learning through simply reading and understanding cannot provide answers in real situations.

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 out loud. 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 it's read as a signal that the conceptual framework is not 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 Um... 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 need to be connected as one coherent 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.

🔥 That's why I created it. The CS Technical Interview Series That Gets You Talking!

🎯 Recommended for these people

Non-majors · Job seekers · Career changers and others who have technical interviews ahead and need to be able to organize CS fundamentals verbally

⚡ Lecture Core Kick

📘 Technical Interview Practical WorkbookProvided

💡 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.

Since childhood, I've been 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 secret note' 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 put all the methods of how to most efficiently understand complex and abstract concepts and make them your own into this course.

• 'Fundamentals' are key in any development field: Whether you're aiming for game development, AI, web/app development, or any other field, basic knowledge of computer science 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, plus 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 one or two sentences during interviews❓

This course is the one and only solution that will quench that thirst of yours.
Rather than simply listing grammar rules, it organizes Java's core concepts with a diagram-centered, principle-centered, and 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 through Java code examples

• How does the JVM operate structurally, and how does GC manage memory?
  → Summarizes 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 common technical interview questions in one or two sentences such as "What are the core principles of OOP?", "Why is GC necessary?", and "When is volatile needed in a multithreaded environment?"

📖 Core-packed Curriculum

Here are the topics 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 :)

🔗 Technical Interview Master Roadmap

Pre-enrollment Reference Information