feat(jdk12): add demo for JEP 230

src/main/java/org/javademos/init/Java12DemoLoader.java

@@ -6,6 +6,7 @@
 import org.javademos.commons.IDemoLoader;
 
 import org.javademos.java12.jep189.ShenandoahExperimental;
+import org.javademos.java12.jep230.MicrobenchmarkSuite;
 import org.javademos.java12.jep325.SwitchExpressionsPreview;
 import org.javademos.java12.jep334.ConstantsAPIDemo;
 
@@ -17,6 +18,7 @@ public class Java12DemoLoader implements IDemoLoader {
     @Override
     public void loadDemos(Map<Integer, IDemo> demos) {
         demos.put(189, new ShenandoahExperimental());
+        demos.put(230, new MicrobenchmarkSuite());
         demos.put(325, new SwitchExpressionsPreview());
         demos.put(334, new ConstantsAPIDemo());
     }

src/main/java/org/javademos/java12/jep230/MicrobenchmarkSuite.java

@@ -0,0 +1,48 @@
+package org.javademos.java12.jep230;
+
+import org.javademos.commons.IDemo;
+
+/// Demo for JDK 12 feature JEP 230 - Microbenchmark Suite.
+///
+/// JEP history:
+/// - JDK 12: [JEP 230 - Microbenchmark Suite](https://openjdk.org/jeps/230)
+///
+/// Further reading:
+/// - [Java Microbenchmark Harness (JMH)](https://github.com/openjdk/jmh)
+/// - [JDK microbenchmarks source](https://github.com/openjdk/jdk/tree/master/test/micro)
+/// - [Microbenchmarking with Java](https://www.baeldung.com/java-microbenchmark-harness)
+///
+/// @author alois.seckar@gmail.com
+public class MicrobenchmarkSuite implements IDemo {
+    @Override
+    public void demo() {
+        info(230);
+
+        // This JEP changes how the JDK itself is developed, not the Java language
+        // or its runtime APIs. A suite of microbenchmarks was added directly into
+        // the JDK source code, so there is nothing new to call from application code.
+
+        // The benchmarks are built on top of JMH (Java Microbenchmark Harness), which
+        // handles the tricky parts of measuring small pieces of code reliably:
+        // JIT warm-up, dead-code elimination, constant folding, forking fresh JVMs, etc.
+        // Naive timing via `System.nanoTime()` around a loop is usually misleading.
+
+        // The suite lives in the JDK repository under `test/micro/org/openjdk/bench`,
+        // split into `java` (organized like JDK packages/modules) and `vm` (organized
+        // like HotSpot components). It originated in the former standalone
+        // "JMH JDK Microbenchmarks" project and started with around a hundred benchmarks.
+
+        // It is not part of a regular JDK build, to keep build times low.
+        // JDK developers can build and run it explicitly, e.g.:
+        //   make build-microbenchmark
+        //   make test TEST="micro:java.lang.reflect"
+        // JMH filtering allows running only the benchmarks of current interest.
+
+        // Co-location makes it easy to add a benchmark together with the code change
+        // it measures, and to compare performance against previous JDK builds/releases.
+        // Benchmarks are expected to be small, stable, and finish within about a minute.
+
+        // To benchmark your own code, add JMH as a dependency to your project and
+        // annotate methods with `@Benchmark` - the same approach the JDK suite uses.
+    }
+}

src/main/resources/JDK12Info.json

@@ -7,6 +7,14 @@
     "link": true,
     "code": false
   },
+  {
+    "jep": 230,
+    "jdk": 12,
+    "name": "JEP 230 - Microbenchmark Suite",
+    "dscr": "Adds a basic suite of JMH-based microbenchmarks to the JDK source code, making it easy to run existing benchmarks and create new ones.",
+    "link": false,
+    "code": false
+  },
   {
     "jep": 325,
     "jdk": 12,