Learning modern Java the playful way

Staying up to date with modern Java can feel overwhelming. If you don’t have any experience with Java since Java 8 (or at all), features like structured concurrency or pattern matching might sound exciting, but also scary: “How do I even get started with that?”

Fear not! In this session Marit and Piotr will explain to you the new exciting things and also show you how to use them in your IDE, so that the next day you can start having fun and profit with modern Java in your favorite tools on your own.

Transcript

1. Learning modern Java the playful way Marit van Dijk, Piotr Przybył JCON MMXXVI
2. Slido for questions
3. $ who are we Piotr Przybył @piotrprz @piotrprz.bsky.social Senior Developer Advocate Docker Captain Marit van Dijk @MaritvanDijk77 @maritvandijk.bsky.social Senior Developer Advocate
4. $ who are you
5. Agenda • Various features from recent Java versions (not all of them, obviously) • Demos (obviously)
6. • More Amber (pattern matching, data-oriented programming) • Loom maturing (Structured Concurrency, Scoped Values) • Panama + Vector API progress (performance, native interop) • Leyden groundwork (startup, footprint) • Stronger security defaults • And more
7. • Performance (Shenandoah, Compact Object Headers) • More concurrency goodies (Scoped Values, revamped Structured Concurrency) • Better observability & profiling • Stuff for newbies / prototyping • And more
8. <Sean Bean portraying Boromir.jpg>
12. Compact source files & Instance main methods Standard feature in Java 25 JEP 512
13. Compact source files & Instance main methods public class HelloWorld { public static void main(String[] args) { System.out.println("Hello World!"); } } void main() { IO.println("Hello World!"); }
14. <Disaster Girl.jpg> Alt: A girl standing in front of a burning house
15. All these pictures are from pixabay.com Stunning royalty-free images & royalty-free stock
16. “an apple on books” Multimodal encoder
17. Multimodal encoder POST elasticsearch/catalogue { "filename" : "apple.png", "embedding" : [0.12, -0.48, 0.0231, …], … } Preparation: Indexing
18. Multimodal encoder POST ${elasticsearch}/catalogue/_search { } “apple” “apple” POST ${elasticsearch}/catalogue/_search { } RRF Results: 1. … 2. … 3. … 4. … Application: Searching ▶
19. Records Standard feature in Java 16 JEP 395 immutable transparent data carriers ▶
20. final class QueryWithVector { private final String query; private final List<Float> vector; QueryWithVector(String query, List<Float> vector) { this.query = query; this.vector = vector; } @Override public String toString() { return "QueryWithVector[" + "query=" + query + ", " + "vector=[" + vector.getFirst() + ", --., " + vector.getLast() + ']'; } public String getQuery() { return query; } public List<Float> getVector() { return vector; } @Override public boolean equals(Object obj) { if (obj -= this) return true; if (obj -= null -| obj.getClass() -= this.getClass()) return false; var that = (QueryWithVector) obj; return Objects.equals(this.query, that.query) -& Objects.equals(this.vector, that.vector); } @Override public int hashCode() { return Objects.hash(query, vector); } } record QueryWithVector(String query, List<Float> vector) { @Override public String toString() { return "QueryWithVector[" + "query=" + query + ", " + "vector=[" + vector.getFirst() + ", --., " + vector.getLast() + ']'; } }
21. Module imports Standard feature in Java 25 JEP 511 ▶
22. Standard feature in Java 25 JEP 512 Compact source files & Instance main methods ▶ Also comes with simple IO
23. Stream Gatherers Standard feature in Java 24 JEP 485
24. Stream Gatherers Stream.of(...) .gather(a) [.gather(b)] [.gather(c)] .collect(...); custom intermediate operations Stream Gatherers - Deep Dive with the Expert: https://youtu.be/v_5SKpfkI2U Gatherers: The API Your Stream Was Missing: https://youtu.be/oVdWfU_IObY Hunting with Stream Gatherers: https://youtu.be/rvW8tu1n5x4 Extending Functional Pipelines with Gatherers: https://www.youtube.com/live/dxVDiJsyu3Y ▶
25. Preview features --enable-preview JEP 12 ▶
26. Structured Concurrency 🧪 Preview in Java 26 JEP 525
27. Structured Concurrency • better "idioms" for multi-threaded code • synchronous way of thinking • help eliminate thread leaks and cancellation delays
28. Task POST ${elasticsearch}/catalogue/_search { } “apple” POST ${elasticsearch}/catalogue/_search { } RRF Results: 1. … 2. … 3. … 4. … Structured Concurrency Subtask Subtask combine Results: 1. … ▶
29. TL;DR: .open() with Joiner and Config, can (re)use thread pools, also platform ones Structured Concurrency try (var scope = StructuredTaskScope.open( StructuredTaskScope.Joiner.awaitAllSuccessfulOrThrow(), Config -> config .withName("myStructuredConcurrency") .withTimeout(Duration.ofSeconds(5)) .withThreadFactory(myThreadFactory))) { var subtask1 = scope.fork(() -> action(--.)); var subtask2 = scope.fork(this-:anotherAction); scope.join(); combineResults(subtask1.get(), subtask2.get()); }
30. CompletableFuture has no future!
31. Lazy Constants 🧪 Preview in Java 26 JEP 526 • Immutable • Thread safe • Lazily evaluated ▶
32. Lazy Constants static final LazyConstant<ObjectMapper> OBJECT_MAPPER = LazyConstant.of(ObjectMapper-:new); -/ and later on OBJECT_MAPPER.get()--. OBJECT_MAPPER.orElse(--.) OBJECT_MAPPER.isInitialized()
34. Markdown Documentation Comments Standard feature in Java 23 JEP 467 • Easier to read & write Markdown in Java Docs? Shut Up and Take My Comments! https://blog.jetbrains.com/idea/2025/04/markdown-in-java-docs-shut-up-and-take-my-comments/ ▶
36. Stay up to date 1. pom.xml / gradle.kts 2. new idioms ▶
37. Pattern matching with primitive types 🧪 Preview in Java 26 JEP 530 • Allow primitive types in all pattern contexts • Extend instanceof and switch to work with all primitive types ▶
38. int memberDiscountPercentage(boolean isGoldMember) { return isGoldMember ? 20 : 5; } int itemDiscountPercentage(int items) { if (items -= 2) { return 5; } else if (items -= 3 -| items -= 4) { return 10; } else if (items -= 5) { return 20; } return 0; } int memberDiscountPercentage(boolean isGoldMember) { return switch (isGoldMember) { case true -> 20; case false -> 5; }; } int itemDiscountPercentage(int items) { return switch (items) { case 2 -> 5; case 3, 4 -> 10; case int i when i -= 5 -> 20; default -> 0; }; }
41. Vector API (Panama) 🧫 Incubator in Java 26 JEP 529 ▶
42. • API to express vector computations • Different performance characteristics
43. <RollSafe.jpg> Alt: A man tapping his forehead
44. $ docker exec -it es-local-dev /bin/sh -c "ps aux | cat" /usr/share/elasticsearch/jdk/bin/java -Des.networkaddress.cache.ttl=60 -Des.networkaddress.cache.negative.ttl=10 -XX:+AlwaysPreTouch -Xss1m -Djava.awt.headless=true -Dfile.encoding=UTF-8 -Djna.nosys=true -XX:-OmitStackTraceInFastThrow -Dio.netty.noUnsafe=true -Dio.netty.noKeySetOptimization=true -Dio.netty.recycler.maxCapacityPerThread=0 --add-opens=org.apache.lucene.core/org.apache.lucene.codecs.lucene99=org.elasticsearch.server --add-opens=org.apache.lucene.core/org.apache.lucene.internal.vectorization=org.elasticsearch.server -Dlog4j.shutdownHookEnabled=false -Dlog4j2.disable.jmx=true -Dlog4j2.formatMsgNoLookups=true -Djava.locale.providers=CLDR -Dorg.apache.lucene.vectorization.upperJavaFeatureVersion=25 -Des.path.home=/usr/share/elasticsearch -Des.distribution.type=docker -Des.java.type=bundled JDK --enable-native-access=org.elasticsearch.nativeaccess,org.apache.lucene.core --enable-native-access=ALL-UNNAMED --illegal-native-access=deny -Des.cgroups.hierarchy.override=/ -XX:ReplayDataFile=logs/replay_pid%p.log -XX:+EnableDynamicAgentLoading -Djdk.attach.allowAttachSelf=true --patch-module=java.base=/usr/share/elasticsearch/lib/entitlement-bridge/elasticsearch-entitlement-bri dge-9.2.0.jar --add-exports=java.base/org.elasticsearch.entitlement.bridge=org.elasticsearch.entitlement,java.loggin g,java.net.http,java.naming,jdk.net -XX:+UseG1GC -Djava.io.tmpdir=/tmp/elasticsearch-12468091459950034174 --add-modules=jdk.incubator.vector -Dorg.apache.lucene.store.defaultReadAdvice=normal -Dorg.apache.lucene.store.MMapDirectory.sharedArenaMaxPermits=1 -XX:+HeapDumpOnOutOfMemoryError -XX:+ExitOnOutOfMemoryError -XX:ErrorFile=hs_err_pid%p.log -Xlog:gc*,gc+age=trace,safepoint:file=gc.log:utctime,level,pid,tags:filecount=32,filesize=64m -Xms128m -Xmx2g -XX:MaxDirectMemorySize=1073741824 -XX:G1HeapRegionSize=4m -XX:InitiatingHeapOccupancyPercent=30 -XX:G1ReservePercent=15 --module-path /usr/share/elasticsearch/lib --add-modules=jdk.net --add-modules=jdk.management.agent --add-modules=ALL-MODULE-PATH -m org.elasticsearch.server/org.elasticsearch.bootstrap.Elasticsearch ▶
45. What did we play with? Vectors from Panama Records Structured Concurrency Stream Gatherers Lazy Constants Pattern Matching Compact Classes, module imports, simple IO … and more
46. Each new Java version is: • easier • faster • better • and (guess what?) still free Why not use it?
49. How was it? bit.ly/LMJPW-JCON
50. The (QR) code & everything bit.ly/LMJPW-all
52. Thank you! Vielen Dank! Piotr Przybył @piotrprz @piotrprz.bsky.social Senior Developer Advocate Marit van Dijk @MaritvanDijk77 @maritvandijk.bsky.social Senior Developer Advocate