Java Fundamentals

This is your baseline Java reference for everything from classic OOP patterns to modern Java 21 features like pattern matching and records. It covers the core language mechanics you'll use daily: collections selection (with an actual decision table for ArrayList vs HashSet vs TreeSet), streams operations, exception handling, and SOLID principles. The quick reference examples are genuinely helpful, showing real patterns like Optional chaining and switch expressions. It spans Java 8 through 21, so you can write code that works across different runtime versions. Think of it as the skill you invoke when you need clean, idiomatic Java without reaching for Stack Overflow every time you forget whether to use flatMap or just map.