How a Junior Backend Engineer Can Prioritize Learning Breadth and Depth and When to Use Java Wrapper Types vs Primitive Types

Background: As a junior backend developer, I feel the knowledge landscape is overwhelming. Horizontally there are algorithms, operating systems, networking, concurrency, middleware, databases, etc.; vertically, each topic can be explored deeply, sometimes seemingly bottomless.

Because of this, in my learning journey I encounter two problems: on the breadth side, "there is too much to master, I don't know where to start"; on the depth side, "a superficial understanding may leave pitfalls" or "I forget details of problems I've studied in depth".

Question: How should I prioritize my learning to develop my abilities, any recommended order? To what extent should I study depth? As a backend engineer, what can be considered a core competency?

2. Java has wrapper classes and primitive types. In daily code, should we use wrapper classes or primitive types, or what conditions distinguish them? At what service scale does it affect performance, and why?

Answer: To improve your technical level, whether in breadth or depth, start from your company or actual projects, encounter problems, solve them, and reflect on the root cause to enhance your skills.

The appropriate "depth" varies per individual and interest. For example, if your business scenario involves selecting one item from tens of millions or billions based on complex conditions, you will likely face performance issues. In such cases, items stored in contiguous memory are faster than random memory, so consider building indexes, updating them in real time, and addressing other practical concerns.

Regarding the core competency of a backend engineer, I would say learning ability. I recommend all engineers solidify fundamentals such as data structures and algorithms from undergraduate computer science courses.