https://devops-monk.com/tags/preview/Recent content in Preview on Devops MonkHugoen-usMon, 04 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/java17/pattern-matching-switch-preview/Mon, 04 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/java17/pattern-matching-switch-preview/Preview Feature in Java 17 (JEP 406 — First Preview). Requires --enable-preview. This feature evolved through Java 18 (JEP 420), Java 19 (JEP 427), Java 20 (JEP 433), and was finalized in Java 21 (JEP 441). The Java 21 final version has minor syntax differences from this Java 17 preview — documented below. Enabling Preview Features Pattern matching for switch requires --enable-preview in Java 17. Add to your build tool:https://devops-monk.com/tutorials/java21/scoped-values/Mon, 04 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/java21/scoped-values/Preview Feature — Requires --enable-preview at compile and runtime. The ThreadLocal Problem at Scale ThreadLocal has been the standard way to pass context (request ID, user session, database transaction) implicitly through a call stack without threading it through every method signature. It works well with a few hundred platform threads. With virtual threads, it breaks down. Problem 1 — Memory overhead with inheritance When you create a child thread with InheritableThreadLocal, Java copies the thread-local map from parent to child:https://devops-monk.com/tutorials/java21/structured-concurrency/Mon, 04 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/java21/structured-concurrency/Preview Feature — Requires --enable-preview at compile and runtime. The API stabilized significantly from Java 21 through 24 and will be finalized in a future release. The Unstructured Concurrency Problem When you submit tasks to an ExecutorService, the tasks are logically related but structurally unconnected — the executor doesn’t know they belong together: // Unstructured concurrency — looks simple, hides serious problems ExecutorService executor = Executors.newCachedThreadPool(); Future<Order> orderFuture = executor.https://devops-monk.com/tutorials/java21/unnamed-classes/Mon, 04 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/java21/unnamed-classes/Preview Feature — Requires --enable-preview at compile and runtime. The Boilerplate Problem Teaching Java to a beginner means explaining class declarations, access modifiers, static, and String[] before they can print “Hello, World!”: // Traditional Java — 4 concepts before printing one line public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"); } } Every word carries meaning, but that meaning is irrelevant until the student understands OOP, the JVM class model, and program entry points.https://devops-monk.com/tutorials/java21/unnamed-patterns/Mon, 04 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/java21/unnamed-patterns/Preview Feature — Requires --enable-preview at compile and runtime. The _ identifier was reserved in Java 9; this JEP gives it formal semantics. The Problem: Forced Naming of Unused Things When pattern matching, you often care about only some components of a matched structure. But the syntax forces you to name everything: record Point(int x, int y) {} record ColoredPoint(Point point, String color) {} record Box(ColoredPoint cp, int weight) {} // You only care about the color — but must name everything else if (obj instanceof Box(ColoredPoint(Point(int x, int y), String color), int weight)) { System.https://devops-monk.com/tutorials/java21/vector-api/Mon, 04 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/java21/vector-api/Preview Feature in Java 21 — The Vector API has been in preview since Java 16 (JEP 338). JEP 448 is the sixth preview iteration in Java 21. The API is stable and production-usable with --enable-preview; finalization is pending Project Valhalla value types. What Is SIMD and Why Does It Matter? Modern CPUs can perform the same arithmetic operation on multiple data values in a single instruction. This is called SIMD — Single Instruction, Multiple Data.