java-tutorial

16) JVM Basics: Memory, GC, Performance Habits

Goal

Build correct mental models for performance without premature optimization.

JVM memory (high level)

• Heap: where objects live
• Stack: method frames, local variables

Garbage collection

• You usually don’t free memory manually.
• Avoid holding references longer than needed.

Practical performance habits

• Prefer clarity first.
• Measure before optimizing.
• Avoid unnecessary allocations in hot loops.
• Use the right data structure.

Exercises

1. Use System.nanoTime() to compare two string-building approaches: + in a loop vs StringBuilder.
2. Read about GC logs (optional): run Java with GC logging flags (varies by version).

Table of contents

1. Getting Started: Install, run, and your first program
2. Java Basics: types, variables, operators, formatting
3. Control Flow: if/switch/loops
4. Methods: parameters, return values, overloading
5. OOP: classes, objects, encapsulation
6. Inheritance & Polymorphism (and when not to use them)
7. Interfaces, abstract classes, and design basics
8. Exceptions and error handling
9. Strings, files, and I/O basics
10. Collections: List/Set/Map and Big-O intuition
11. Generics (the useful parts)
12. Lambdas & Streams
13. Dates and time (java.time)
14. Testing with JUnit 5 (basics)
15. Concurrency: threads, executors, futures
16. JVM basics: memory, GC, performance habits
17. Build tools: Maven essentials (recommended)
18. Next steps: projects to build