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Java - Wyatt's Notes

Java programming language notes covering fundamentals, advanced concepts, and practical examples.
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sources:

  • text: Standard textbook reference

Java is a programming language with a rich type system and ecosystem. These notes cover the language from fundamentals to advanced topics, with worked examples, practice problems, and flashcards.

Topics

Fundamentals

Java fundamentals notes covering key definitions, core concepts, worked examples, and practice problems.

Object oriented

Java object oriented notes covering key definitions, core concepts, worked examples, and practice problems.

Collections

Java collections notes covering key definitions, core concepts, worked examples, and practice problems.

Streams

Java streams notes covering key definitions, core concepts, worked examples, and practice problems.

Concurrency

Java concurrency notes covering key definitions, core concepts, worked examples, and practice problems.

Best practices

Java best practices notes covering key definitions, core concepts, worked examples, and practice problems.

Modern java

Java modern java notes covering key definitions, core concepts, worked examples, and practice problems.

Jvm internals

Java jvm internals notes covering key definitions, core concepts, worked examples, and practice problems.

Io nio

Java io nio notes covering key definitions, core concepts, worked examples, and practice problems.

Generics reflection

Java generics reflection notes covering key definitions, core concepts, worked examples, and practice problems.

Exceptions

Java exceptions notes covering key definitions, core concepts, worked examples, and practice problems.

Build tools

Java build tools notes covering key definitions, core concepts, worked examples, and practice problems.

Intuition

Java’s ecosystem is its greatest strength: Beyond the language itself, Java has Maven, Spring, JUnit, and thousands of libraries that make building enterprise applications practical. The JVM provides performance, portability, and garbage collection.

Why it matters: Java remains one of the most widely used languages in enterprise, Android development, and big data processing.

The key insight: Java’s verbosity is deliberate — explicit code is easier to read, debug, and maintain, especially in large codebases with many developers.

What You Will Find

  • Fundamentals: Types, control flow, exception handling, and the collections framework
  • Object-Oriented: Classes, interfaces, inheritance, and design patterns
  • Concurrency: Threads, executors, locks, and concurrent data structures
  • JVM Internals: Class loading, garbage collection, and JIT compilation
  • Modern Java: Records, sealed classes, pattern matching, and virtual threads

Why This Matters

Java remains one of the most widely used languages in enterprise software, Android development, and large-scale distributed systems. Its mature ecosystem, strong type system, and JVM performance make it a reliable choice for production systems. Understanding Java’s concurrency model, memory management, and class loading system is essential for building scalable, maintainable applications.

Common Mistakes

Assuming Java is slow because of the JVM: Modern JVMs use JIT compilation, garbage collection optimisations, and intrinsic methods. Java performance is competitive with C++ for many workloads. The JVM overhead is often negligible compared to algorithmic efficiency.

Overusing static methods: Static methods cannot be overridden or mocked efficiently, making testing harder. They also create tight coupling. Prefer instance methods and dependency injection for testable, maintainable code.

Ignoring the Java Memory Model: Concurrent programming in Java requires understanding the Java Memory Model. Without proper synchronization (volatile, synchronized, java.util.concurrent), thread interactions may not see each others writes due to caching and reordering.

Cross-References

  • Site Home: Main landing page for Java notes.
  • Java Basics: Fundamental Java concepts including types and control flow.
  • Concurrency: Multithreading and concurrent programming.
  • Practice: Practice problems for revision.