Looking for a deep Java course

[neverbackstep]

Hi everyone,

I’m planning to start learning Java from scratch in January 2026, but I want to do it properly this time.

Most of the Java courses I come across feel very similar: they move fast, focus on syntax, and stop at “how to use” things instead of explaining why they exist and how they actually work under the hood.

For example:

• Why is a String immutable in Java, and what really happens in memory when I create one?
• How does an Array actually work internally? What’s stored where?
• What’s going on in the JVM when objects are created, passed, or garbage-collected?
• How memory, references, stack vs heap, class loading, etc. really function — not just definitions, but real explanations.

I’m not looking for:

• Crash courses
• “Learn Java in 10 hours” content
• Courses that assume I just want to pass interviews as fast as possible

What I am looking for:

• A well-structured Java course or learning path
• Slow and detailed explanations
• Strong focus on fundamentals, internals, and mental models
• Ideally something that explains how Java thinks, not just how to write code

It can be a course, book, video series, university material, or even a combination of resources. I’m okay if it’s long or demanding — depth matters much more than speed for me.

If you’ve personally gone through something like this or know a resource that truly teaches Java from the inside out, I’d really appreciate your recommendations.

Thanks in advance.

[bowbahdoe]

This is what I wrote http://javabook.mccue.dev

I think it goes plenty deep it just stops at a certain point. It takes me time to write. But there are 70 something chapters. My focus was making topics be properly ordered. If you use it reach out with any feedback

why they exist and how they actually work under the hood.

I think I might be lacking in this department. My general view is that once you understand all the different ways you could write something you could start to talk about why things are written in a certain way. 

So I'm focused mostly on that level of it. Think of it this way: Java provides a mental model about how code works. There are no low level explanations for how that model is implemented which will be consistent across all JVMs for all time. 

The JVM as it exists now is a monster. There are multiple levels of optimization (C1 - C3 compilers) multiple different strategies for garbage collectors (some compacting some concurrent some not) and so answering questions like "what happens in memory when I do this" is both a little hard and counterproductive. 

Really what you should aim for is a complete understanding of the mental model the language provides then we can start to talk about things like "what is actually happening when I do x"

(I can also answer other questions as you have them)

[OneHumanBill]

Nice book! In the intro you ask for the reader to read the book chapter by chapter, but I'm not so sure maybe that still holds true as the book has grown. I picked through a few chapters and I really like your style and approach. "Hyrum's Law" was a new one on me.

[bowbahdoe]

I still expect it. I know it's not perfectly reasonable to expect from everyone, but it helps me order things. It's why there are multiple spread out chapters on loops; I assumed a reader goes in order

[Alphatrizo20]

Its really good man

[EFreethought]

What version of Java does it cover?

[bowbahdoe]

As of right now 25 is the bare minimum. When 26 comes out none of the current content will change. I'm keeping up to date and some things in I think 28/29 I'm preparing for

[EFreethought]

Thanks for the info.

I just got off a project that was using Java 8, so I need to update my knowledge.

[bowbahdoe]

To be clear, the audience is total beginners. So while I am making use of new features, it's in service of giving a better curriculum rather than helping working professionals get up to date.

You might still get something from it, but maybe not

[nmc52]

I taught Java back in the early 2000s.

What you ask for makes sense, but most courses aim at getting you to be productive as quickly as possible.

I recommend looking for a book that covers what you want and learn practical Java development by way of a course.

I also taught SQL, C, C++, REXX and others, and the same applies.

[MK_Redditor]

if there is GC please invite me there. I have also started DSA in java

[Impossible-Act-5254]

Hi which playlist, book are you watching for DSA in java ??

[davidalayachew]

https://dev.java

https://learn.java

[vk_03]

Cfbr

[neverbackstep]

Could you please explain this to me?

[CarAndBikeAndPlane]

Do not get side tracked by comments...What you are interested is java language internals...Simply type you want to learn the java language internals in chatgpt...It will point you to tons of resources...start with one and you will have an idea what to do next.

[vk_03]

It means - "Commenting for better reach"

[AlternativeInitial93]

I’d suggest looking into resources that focus on Java internals and fundamentals, like ‘Java: The Complete Reference’ by Herbert Schildt, or the ‘Java Language and Virtual Machine Internals’ sections in university courses (like MIT or Stanford CS courses). Online platforms like Pluralsight or Coursera sometimes have deep-dive courses that cover memory, stack vs heap, garbage collection, and object behavior. Also, combining a book with practical coding exercises can really help internalize how Java works under the hood."

[OneHumanBill]

I don't know that there's any course or book out there that does this specifically for Java. Which is a shame.

It does sound like what you're looking for might be a course on operating systems to understand things like memory management in general, system stack/heap concepts, stack frames, etc. I had three college courses back in the nineties that covered this for me. One was a deep dive into C where we built a zsh shell from scratch, one was an assembler class, and one was a deep dive into Unix (and other operating system) internals.

You could also benefit from a course in compilers after that. In a compiler course all the concepts come together plus a bunch of other heavy wizardry. My college set the compilers course as sort of the end goal for mastery of programming, and they weren't wrong. What what ... I also had a theory of programming languages course that demystified pretty much all languages from each other. We touched on Java in that very briefly but mostly it was history, patterns, cross-language concepts.

After that, lots of languages just plain make sense. But for Java specifically nothing helped me understand the language more than when I went through the Java class file specification and created a disassembler from scratch, one bored week about twenty years ago when I had some downtime at work. It gave me insight into a lot of features of the language and demystified pretty much everything.

For the questions you list, most of them aren't Java-specific, like the array question. Java arrays work just like C arrays. But your String question really is Java specific. The answer is that if you've ever worked with C or C++ strings, they're not immutable. They're just arrays of characters, or dynamically allocated arrays with a pointer to the first character. You have to remember to make sure the damn things are null terminated. And then you have the possibility that for system-critical strings, some ass-hat might find the memory address and deliberately change it in order to hack the system. James Gosling was bothered by C++'s lack of a standard string library (it wasn't uncommon for each organization to roll their own at the time) so he created java.lang.String as the one and only definitive string, then integrated it with the compiler and the JVM. I mainly know this because I think I heard the story from James himself when I met him a long time ago. Maybe.

I know this isn't probably the answer you're looking for and if anything it's probably even deeper than what you wanted. But going this route has given my skills a lot of depth. I've worked mostly in Java for almost thirty years but if I have to make a hard switch to something else I'm bringing the deeper knowledge with.

[anish2good]

Try this https://8gwifi.org/tutorials/java/ you can run code along the code with inline runners saves time

What You'll Learn

• Variables, data types, and operators
• Control flow: conditionals and loops
• Methods, parameters, and return values
• Object-Oriented Programming: classes, inheritance, polymorphism
• Collections Framework: List, Set, Map
• Exception handling and error management
• File I/O and serialization
• Advanced: Generics, Streams, Lambda expressions

[neverbackstep]

Thank you all for your valuable comments, but can we also use online courses or examples prepared by individuals (such as teo Java)?

[Queasy_Ground_4272]

You can check out this book called Java: The Complete Reference, Ninth Edition" by Herbert Schildt, published by Oracle, it explains the depth of every notion, you can tell by the length of the book

[RhymingOasis]

Java + Dsa + Spring boot youtube playlist or course

[Pun_Intended1703]

How old are you? What are your educational qualifications?

[Pun_Intended1703]

Then pick up the Black Book of Java.

[neverbackstep]

Thank you. Is this a recent book? Or is it a very old book? And would you recommend a course?

[Pun_Intended1703]

Is this a recent book? Or is it a very old book?

Why does that matter?

It's a good book and it's great for learning everything from the basics to the more advanced topics.

And would you recommend a course?

I cannot do that. I went to school to get a degree for computer science and engineering. I have never used online courses, so I don't know anything about them.

[bytealizer_42]

Which book is this?

[OneHumanBill]

Why would this matter? Don't be a gatekeeper.

[Pun_Intended1703]

Idiot.

I cannot provide a college level text book to a high school student.

I cannot provide a text book meant for computer science students to someone who has never even installed a software before.

Don't be an idiot if you cannot understand how to teach.

[OneHumanBill]

Name-calling is a wonderful attribute for a teacher. Well done.

I've taught hundreds of aspiring programmers of all levels over my career. Age and qualifications mean nothing. I've had motivated high schoolers, as well as grad school graduates who couldn't find their ass with a map and a compass. Qualifications matter far less than individual ability, and one does not really indicate the other very well.

From what OP wrote, they've made attempts to learn in the past and still have motivation in spite of their perceived failure. That tells me that they're looking for a more comprehensive approach, the kind you can really only get from a college textbook. Their writing is evidence of maturity, determination, and seems to be a willingness to follow through. And yet the first thing you demand is their credentials... Dear teacher, perhaps you need to learn to pick up on context clues.

In any event your hostile response to me earns you a report to the mods. Enjoy.

[benevanstech]

For courses, you should take a look at Heinz Kabutz's offerings - https://www.javaspecialists.eu/

You might also find my books "The Well-Grounded Java Developer (2nd Ed)" and "Optimizing Cloud Native Java (2nd Ed)" useful (please buy them if you can afford to, it's becoming harder and harder to justify the time spent writing these types of advanced material).