Java Version Evolution

Why Java 8 is the single biggest shift in the language's history: lambda expressions and functional interfaces, the Streams API for declarative data processing, Optional for explicit absence, and the default/static methods and method references that made it all fit together.

After the Java 8 earthquake, Java moved to a faster, yearly release train and spent seven versions quietly laying groundwork: the module system reshaping the platform itself, var easing verbose declarations, and a steady drip of previews -- records, text blocks, switch expressions, sealed classes, and pattern matching for instanceof -- that would later combine into Java 21's modern baseline.

Java 17, the second LTS release after 8 and 11, finalizes sealed classes -- a way to tell the compiler exactly which classes are allowed to extend a type, turning open-ended hierarchies into closed, exhaustively-checkable ones, and setting up exactly what pattern matching for switch needed to become safe.

Three transitional releases that fixed a decades-old default encoding inconsistency and ran the final preview rounds of virtual threads and pattern matching for switch -- the last stretch of groundwork before Java 21 locked everything in as a long-term-support baseline.

Java 21, the third LTS since Java 8, is where nearly everything previewed since Java 14 finally locks in at once: record patterns, finalized pattern matching for switch, and Sequenced Collections -- a genuinely new collection abstraction with real depth of its own -- plus virtual threads and structured concurrency shipping as finished features, covered in full elsewhere in this platform.

What's shipped since the Java 21 baseline: unnamed variables and patterns, Stream Gatherers moving from preview to finalized, primitive types joining pattern matching, and a look at Java 25 as the next LTS and Java 26 as the current bleeding edge -- framed as a trajectory to track rather than a frozen list of facts.

A practical capstone: how to actually move a real codebase across the 8-to-11-to-17-to-21 LTS boundaries, a full before/after worked example that modernizes one method using streams, records, pattern matching, and sealed classes together, and a framework for deciding which JDK a brand-new project should target today.