Java Version Upgrades - ashishranjandev/developer-wiki GitHub Wiki

You're asking about a significant jump in Java versions! Going from Java 8 to Java 11 means skipping over Java 9 and Java 10, each of which introduced important features. Here's a breakdown of the key changes across those releases:

Java 8 (March 2014)

  • This is your starting point, and it was a massive release.
  • Lambda Expressions: Enables functional programming with concise, anonymous functions.
  • Streams API: Introduces a powerful way to process collections of data in a declarative style.
  • Default Methods in Interfaces: Allows adding new methods to interfaces without breaking existing implementations.
  • Date and Time API (java.time): A completely revamped date and time API to address the shortcomings of the old Date and Calendar classes.

Java 9 (September 2017)

  • Project Jigsaw (Module System): This was the headline feature, modularizing the JDK itself and allowing developers to create modular applications.
  • JShell (REPL): A Read-Eval-Print Loop for interactive Java coding.
  • Private Interface Methods: Allows defining private helper methods within interfaces.
  • HTTP/2 Client (Incubator): A new HTTP client API supporting HTTP/2.

Java 10 (March 2018)

  • Local-Variable Type Inference: The var keyword allows the compiler to infer the type of local variables.
  • Parallel Full GC for G1: Improved garbage collection performance.
  • Collection Modifications to Interfaces: Minor additions to the Collection interfaces.

Java 11 (LTS - September 2018)

  • Local-Variable Syntax for Lambda Parameters: You can use var when declaring lambda parameters.
  • HTTP Client (Standard): The HTTP Client API from Java 9 becomes standard.
  • Nest-Based Access Control: Improved encapsulation of nested classes.
  • Epsilon Garbage Collector: A no-op garbage collector for short-lived, latency-sensitive applications (experimental).
  • ZGC (Experimental): A scalable low-latency garbage collector.

Key Themes and Trends:

  • Functional Programming: Java 8's lambdas and Streams API paved the way for more functional-style programming.
  • Modularity: Java 9's module system was a fundamental change to how Java applications are structured.
  • Performance: Continuous improvements to garbage collection and other areas to boost performance.
  • Developer Productivity: Features like local-variable type inference aim to make coding faster and more concise.

Migrating from Java 8 to Java 11:

  • While Java is generally backward compatible, migrating from Java 8 to 11 can require some effort.
  • Module System: If your application uses internal JDK APIs, you may need to adjust your code due to the module system's encapsulation.
  • Deprecated APIs: Some APIs deprecated in earlier versions may have been removed.
  • Garbage Collection: You might want to explore the newer garbage collectors (G1, ZGC) for potential performance gains.

Java has adopted a six-month release cadence, with Long-Term Support (LTS) releases every few years. Java 11 and Java 17 are both LTS releases, meaning they receive extended support. Here's a breakdown of the key changes introduced between Java 11 and Java 17:

Java 11 (LTS - September 2018)

  • Local-Variable Syntax for Lambda Parameters: You can use var when declaring lambda parameters.
  • HTTP Client (Standard): A new HTTP Client API replaces the old HttpURLConnection, with support for HTTP/2 and WebSockets.
  • Nest-Based Access Control: Improved encapsulation of nested classes.
  • Epsilon Garbage Collector: A no-op garbage collector for short-lived, latency-sensitive applications (experimental).
  • ZGC (Experimental): A scalable low-latency garbage collector.

Java 12 (March 2019)

  • Switch Expressions (Preview): Enhanced switch statements with arrow syntax and the ability to return values.
  • Shenandoah GC (Experimental): Another low-pause-time garbage collector.
  • Teeing Collector: A new collector in the Stream API to collect stream elements into two collectors.

Java 13 (September 2019)

  • Text Blocks (Preview): Multi-line string literals.
  • Switch Expressions (Second Preview): Further refinements.
  • Dynamic CDS Archives: Improved application class-data sharing.

Java 14 (March 2020)

  • Records (Preview): A concise syntax for declaring data classes.
  • Pattern Matching for instanceof (Preview): Simplified type checking and casting.
  • Helpful NullPointerExceptions: More informative NullPointerException messages.

Java 15 (September 2020)

  • Sealed Classes (Preview): Allows defining restricted class hierarchies.
  • Text Blocks (Second Preview): Further refinements.
  • Hidden Classes: Classes that cannot be discovered directly by other classes.

Java 16 (March 2021)

  • Records (Second Preview): Further refinements.
  • Pattern Matching for instanceof (Second Preview): Further refinements.
  • Vector API (Incubator): An API to express vector computations.

Java 17 (LTS - September 2021)

  • Sealed Classes: Standardized.
  • Records: Standardized.
  • Pattern Matching for instanceof: Standardized.
  • Restore Always-Strict Floating-Point Semantics: Restores the original floating-point behavior.
  • Enhanced Pseudo-Random Number Generators: New interfaces and implementations for random number generation.

Key Themes and Trends:

  • Language Enhancements: Improvements to syntax and semantics for increased developer productivity (e.g., Records, Pattern Matching, Text Blocks).
  • Performance and Garbage Collection: Ongoing work on improving garbage collection algorithms (ZGC, Shenandoah) and introducing new performance-oriented features (Vector API).
  • API Improvements: Enhancements to existing APIs and introduction of new ones (e.g., HTTP Client, RandomGenerator).
  • Preview Features: Gradual introduction and refinement of new features through preview phases before final standardization.

It's tricky to give you a complete, detailed explanation of every change in each Java release from 17 to 23. The OpenJDK project moves very quickly, with lots of small tweaks and bug fixes. However, I can highlight the major features and trends in those releases:

Java 17 (LTS - September 2021)

  • This is where we start, an LTS release, meaning long-term support.
  • Sealed Classes: Formalized, allowing you to control which classes can inherit from a class or interface.
  • Records: Formalized, providing a concise syntax for creating immutable data classes.
  • Pattern Matching for instanceof: Formalized, simplifying type checking and casting.

Java 18 (March 2022)

  • Simple Web Server: A basic command-line HTTP server for prototyping and testing.
  • Code Snippets in Java API Documentation: Ability to include executable code examples in Javadoc.
  • Vector API (Third Incubator): Continued development of the API for vector computations.

Java 19 (September 2022)

  • Virtual Threads (Preview): Lightweight threads that dramatically reduce the effort of writing, maintaining, and observing high-throughput concurrent applications.
  • Structured Concurrency (Incubator): An API to simplify multi-threaded programming by treating multiple tasks running in different threads as a single unit of work.
  • Record Patterns (Preview): Enhancements to pattern matching to deconstruct record values.

Java 20 (March 2023)

  • Record Patterns (Second Preview): Further refinements.
  • Virtual Threads (Second Preview): Further refinements.
  • Scoped Values (Incubator): A mechanism to share immutable data within and across threads.

Java 21 (LTS - September 2023)

  • Virtual Threads: Formalized.
  • Scoped Values (Preview): Further refinements.
  • Record Patterns: Formalized.
  • Sequenced Collections: New interfaces to represent collections with a defined encounter order.
  • Generational ZGC: Improvements to the Z Garbage Collector to improve performance.

Java 22 (March 2024)

  • Statements before super(...): Allows statements that don't access instance members to appear before the super() call in constructors.
  • Implicitly Declared Classes and Instance Main Methods (Second Preview): Streamlines writing simple programs.
  • Foreign Function & Memory API (Third Preview): Enables Java programs to interoperate with code and data outside the Java runtime.

Java 23 (September 2024)

  • Primitive Types in Patterns, instanceof, and switch (Preview): Allows the use of primitive types in pattern matching.
  • Stream Gatherers (Second Preview): New intermediate operations for the Stream API.
  • Structured Concurrency (Third Preview): Further refinements.
  • Scoped Values (Third Preview): Further refinements.

Key Trends:

  • Concurrency and Performance: A major focus on improving concurrency with features like Virtual Threads and Structured Concurrency, and enhancing garbage collection with ZGC improvements.
  • Pattern Matching Enhancements: Continuously improving pattern matching to make code more concise and expressive.
  • Project Loom: This umbrella project is delivering features like Virtual Threads and Structured Concurrency, fundamentally changing how concurrent applications are written in Java.
  • Project Panama: This project aims to improve interoperability with non-Java code and memory, with the Foreign Function & Memory API.