I'm studying these now! | 정진영의 포트폴리오

Machine Learning

Mon, 13 Oct 2025 00:00:00 +0000

Machine Learning Study Log: Teaching a Computer with Data

As I entered the fall semester of my junior year, I began taking a course called “Machine Learning”. I’m attending Professor Song Hyun-je’s lectures every Monday and Wednesday at 4:00 PM in Room 523 of Engineering Building 7. You can find more information on Professor Song Hyun-je’s site via the link attached above!

At first, the term “Machine Learning” felt very difficult and complex. However, now that I’ve started learning it, I’ve realized it’s a fascinating technology that is much closer to our daily lives than I expected. I’ve decided to summarize the basic ML concepts I’ve learned in my own simple words.

🧐 So, what is Machine Learning? My understanding is that machine learning starts with a very simple idea. Instead of explicitly telling a computer every single rule (e.g., “this is an apple,” “this is an orange”), it is a technology that lets the computer learn patterns and rules on its own by showing it vast amounts of data.

It’s similar to how a young child might look at hundreds of pictures of dogs and come to realize on their own, “Ah, an animal with perky ears and fluffy fur is a dog!”

📚 Two Learning Methods I’ve Learned There are many types of machine learning, but I have learned about the two most representative methods.

Teaching with the “Answer Key”: Supervised Learning Supervised learning is, as the name suggests, a method of training a computer using data that already has the “answer” (known as a Label). It works by repeatedly showing the computer sets of “problems” and “answers” together.

A spam filter is a classic example. By training the model on countless emails (problems) labeled as “this is spam” (answer) or “this is important” (answer), it eventually learns to classify new, unseen emails on its own.

Housing price prediction is another example. If it learns from vast amounts of housing data (problems) like, “A 3-bedroom house in Area A costs $500,000” (answer), it will be able to predict the price when given information about a new house.

Letting it Learn on its Own: Unsupervised Learning Unsupervised learning is like giving the computer raw data without any answers and telling it, “Find some meaningful groups or structures within this!” The computer analyzes the features of the data and groups similar items together by itself.

This is very useful for customer management. By feeding it customer purchase pattern data, the model can discover hidden customer segments, such as a “budget shopper group” or a “new product enthusiast group.”

News article clustering is another great example. When given thousands of news articles, the AI can automatically bundle them into similar topics like “Politics,” “Economy,” or “Sports.”

✨ Closing Thoughts Now that I’ve learned the concepts firsthand, I feel that machine learning isn’t some vague, abstract technology, but rather a very logical tool for solving problems. Of course, I still only know the absolute basics, but I find the process of discovering meaning within data to be truly fascinating. I’ve now set a goal for myself to study this more deeply and to try and build a simple project of my own.

JAVA

Sun, 12 Oct 2025 00:00:00 +0000

I began this study not just to simply understand Java’s syntax and features, but to deeply explore why those features are necessary and how they can be applied in practice.

The topics I have studied so far are as follows.

Object Class

The Object class is the top-level parent of all classes. I studied the reasons why the Object class is necessary, the features it provides, and also learned about the concepts of identity vs. equality in Java through the equals() method.

Immutable Objects

An immutable object is an object whose state cannot be changed after it is created. Many objects provided by Java—including String, wrapper classes, and date/time objects—are immutable. I studied why immutable objects are necessary and how to create them.

String Class

The String class is used for handling character strings in Java. I studied not only the basic features of String objects but also the functional and performance differences between StringBuilder and String, as well as how Java optimizes the String class.

Wrapper & Class Classes

I learned about the limitations of Java’s primitive types and studied the wrapper classes designed to overcome them. Additionally, I studied the Class class, which represents class information, the System class, which provides system information, and other frequently used classes like Math and Random.

Enumerations (Enums)

Enums are an excellent feature that provides a high level of type safety. Rather than just learning the syntax, I studied the fundamental reasons why enums are necessary. I also tried implementing the “typesafe enum pattern” that was manually implemented in the days before enums existed.

Nested and Inner Classes

Placing a class within another class is known as a nested or inner class.

Exception Handling

While Java’s exception handling syntax is simple, I studied why exception handling is necessary.

Spring MVC

Sun, 12 Oct 2025 00:00:00 +0000

##From Servlets to Spring MVC: Learning the Evolution of Java Web Development This time, I took the opportunity to trace the evolution of web applications, a technology that can be called the core of Java backend development.

Why Web Applications? Most modern applications operate in a web environment. The countless services we use every day are, in fact, web applications. Java backend developers play a critical role in developing the server-side logic for these applications, and the most powerful tool used for this is the Spring Framework—specifically, Spring MVC.

To gain a deep understanding of Spring MVC, which helps us develop complex web applications quickly and easily, I studied its foundational technologies step-by-step, starting from its very roots.

The Beginning of Java Web Tech: Servlets Everything started with Servlets. A Servlet is pure Java code that receives a client’s request, processes business logic, and generates a dynamic HTML response. However, this approach had a major drawback: HTML code had to be written directly within the Java code as strings (e.g., out.println("…")). This made modifying the view (the UI) cumbersome and severely harmed readability.
Separating the View: JSP (JavaServer Pages) JSP emerged to compensate for this shortcoming. JSP is a technology that allows embedding Java code within an HTML document, which made collaboration between designers and developers much easier. Thanks to this, the task of presenting the view became much more manageable.

But JSP alone was not enough. Business logic and presentation code were still mixed in a single file. As projects grew larger, this led to “spaghetti code,” which became increasingly difficult to maintain.

The Start of Role Separation: The MVC Pattern To solve this problem, a design philosophy called the MVC (Model-View-Controller) pattern emerged.

Model: Manages the data and business logic.

View: Manages the screen (UI) shown to the user. (JSP)

Controller: Acts as the intermediary, receiving the user’s request and connecting the Model and View. (Servlet)

By clearly separating these roles, the code became much more structured and reusable.

The Birth of Spring MVC and its Practical Use Implementing the MVC pattern manually still involved a lot of repetitive and cumbersome work. Developers began to create MVC frameworks to make using this pattern easier, and the most successful and overwhelmingly popular of these became Spring MVC.

Spring MVC handles the complex processes required for MVC implementation on behalf of the developer, providing an environment where one can focus solely on the business logic. This study covered everything from the origins of Spring MVC to the modern techniques used in the field, allowing me to personally understand why countless companies choose Spring.

I will continue to share my experiences as I conduct my own projects using these technologies. Thank you!

You can check out the code I’ve studied so far via the link attached above!