Real-World Java - Advanced Part 3, Lambda, Streams, and Functional Programming by Kim Young-han

The best choice I made before enlisting 😊 ++ After completing the course: I first learned Java last year when I entered university. There, I came across Kim Young-han's lectures through a recommendation from a senior, and I was very impressed with the way he explained everything from the principles, step by step, in the introductory and basic courses, even though I knew nothing. Thanks to the hand-drawn illustrations and well-organized PDFs, I was able to learn Java in a fun way and build a solid foundation. And while learning the intermediate and advanced courses, I think I fell in love with the charm of Java and object-oriented programming with fun elements like various design patterns. I started last year and learned a lot while taking Young-han's Java roadmap from the introductory to advanced courses for a year. Thanks to that, I got an A+ and I'm grateful! I'm also looking forward to any additional lectures! Thank you.

Hello Younghan, first of all, congratulations on successfully completing the Java roadmap! I was really looking forward to this third Java installment, as it covers modern syntax (Lambda, Stream) that I've been wanting to learn so much. I initially intended to take the wild course, but after facing setbacks with Lambda and Optional in the Spring introduction, I decided to complete the entire Java roadmap first. Starting with the introduction, I've now reached the final lecture. Having taken all the Java roadmap courses and reviewed them at least twice, I believe this Java roadmap is truly "an in-depth course based on programming and computer science, not just a simple Java language course." In the past, I had tried to understand Lambda syntax by haphazardly searching through books or online, but I never fully grasped how to actually use it. I tend to be intimidated by unfamiliar terms like functional programming and Lambda. However, from the very beginning of this lecture, the statement "Everyone, Lambda is also an object" immediately helped me understand the content that I had previously found difficult. I wondered why my university professor never mentioned that Lambda is an object, which made me go through so much trouble, and I felt grateful to Younghan for making me understand it with just that one sentence.😆😆😆. Through the introductory and basic courses, I was able to solidify my Java fundamentals. Through the intermediate course, I clearly understood how to handle exceptions and which data structures to use in different situations, and I attempted my first coding test. Through the advanced course 1, I learned about multithreading -> frameworks utilizing multithreading. Through the advanced course 2, I got a taste of how to create dynamic programs through networking and reflection. And through this advanced course 3, I was able to learn about Java syntax that is already commercialized, even though it is considered modern. Also, throughout this entire process, I naturally acquired a lot of computer science knowledge without specifically studying it. In particular, when I first encountered the SOLID principles, I didn't easily understand what each principle meant. However, when I reread the principles towards the end of this roadmap, I realized that they were composed of things that I already considered obvious. Although I may not be able to create something immediately with these advanced skills I've learned, I believe I've taken a step towards Spring, and I'll diligently follow the Spring roadmap as well! "Everything is an object in Java!" "All functions are not some magical trick, but functions written in Java code!" I will keep these two statements in mind and review diligently. I wish you continued success, and once again, congratulations on completing the Java roadmap!

When I first studied lambda expressions and streams, I used the book "Modern Java in Action." While reading this book, I felt like I was getting familiar with these technologies, and I thought the explanations were very well done. But after taking this course up to the streams section, I can confidently say that this course is overwhelmingly better. I haven't studied much, and maybe it's because my skills are lacking that I found other books/courses difficult, but this is the best course/book I've ever encountered. I loved that it didn't feel like the sections were divided, but rather connected, which allowed me to follow the flow. Although I felt there weren't many examples, each example was excellent. I'm currently taking the last course in Younghan's roadmap, and I think this is the best of all the courses. I don't think there's a better course/book for learning lambda expressions/streams for the first time, and I also don't think there's a better course/book for reorganizing your knowledge even if you already know them to some extent. I just wrote this in a stream of consciousness, so the writing is a bit of a mess, but either way, this course is divine. Thank you for creating such a great course. It seems like I can't leave more than two reviews, so I deleted the existing review and rewrote it. 😭😭

Hello! While taking this lecture, I could feel the beauty that the instructor talked about. Truly, the more I listened to the lecture, the more amazing and interesting the time became. It seems I also feel a sense of regret, to the point where this lecture felt exceptionally short. That's how much I think instructor 김영한 gave a good lecture. Now that you have completed the Java Roadmap, I want to say you truly worked hard. Actually, knowing that this lecture was prepared, edited, pondered over again and again, and uploaded by you alone, I think I also approached it with a passionate attitude, inspired by the instructor's passion. I am currently a 4th-year student in the Department of Computer Engineering at university. I am currently taking a lecture on learning the Spring Framework for backend programming, and what I felt while listening was that my coding skills truly improved several times over, just as the instructor said, like a sponge absorbing. In my current project as well, by applying the Lambda technology I just learned where it can be applied, I was able to become even closer to Lambda. Thank you for coming with such a good lecture this time too! I will continue to strive to become a steadily progressing developer! In my path as a developer, instructor 김영한 is a reliable presence, as if walking together. I respect you!! Thank you!

Hello, Younghan!! I finally finished the last part of the Practical Java series, Advanced Part 3! I've been using lambdas, but without really understanding how they work or being aware of the concepts - I just implemented them based on what I was familiar with. After taking your lecture, I feel like my understanding of lambdas has really improved. Now I understand why we write it this way! I sometimes wonder what it would have been like if I had found this course earlier, but I think it's not too late even now. Although I'm still not completely comfortable with lambdas, I'll keep reviewing what you taught me and work on getting more familiar with them haha. Thank you always for making things so easy to understand. You worked so hard to complete the 'Practical Java Roadmap'. Thanks to you, I was able to build a solid foundation (though it was difficult), and I think I'll be able to absorb and understand new things much faster now haha. Tomorrow is Christmas, so have a great Christmas and Happy New Year🙇‍♀️ Looking forward to learning from you in '26 as well! +) You were the instructor I spent the most learning time with in '25 haha. I was so happy to be able to learn together for such a long time. It was a year where I gained a lot of knowledge I didn't have before. But since there's still so much to learn, I'll continue studying diligently in '26 as well haha

I came to write a review while listening to lecture 34. I've taken a few of Kim Young-han's lectures before, and I just thought he was a smart guy, but this curriculum made me think "Wow, this is amazing!" Without fully understanding the teacher's profound intentions, I will study hard!!

I trust Younghan hyung!

Younghan's lectures have an incredibly well-structured build-up. Even if you had worked in construction, you would have been extremely good at it. The content learned over several hours becomes the foundation, giving the feeling of "Ta-da! Java does all these complex things for you!" But more importantly, the lecture seems to focus on "showing how Java's features came to work in historical order." It would be possible to learn Java quickly without Younghan's build-up process and be deployed to real work. There are probably many people who do that. But if deployed that way, would it be possible to improve performance and debug in complex systems? I think it's important to see the inner history of languages that are following the same path as Java. In that sense, the lecture is long, but for me, it felt short. Thank you for everything so far, and I look forward to working with you in the future.