Learning modern Java the playful way (Devoxx PL)

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.

* Talk with Piotr Przybył

Transcript

1. Learning modern Java the playful way Marit van Dijk, Piotr Przybył Devoxx PL MMXXV
2. $ who are we Piotr Przybył @piotrprz @piotrprz.bsky.social Senior Developer Advocate Marit van Dijk @MaritvanDijk77 @maritvandijk.bsky.social Developer Advocate
3. $ who are you
5. Agenda • Various features from recent Java versions (not all of them, obviously) • Demos (obviously)
6. CAVEAT AVDITORES A.K.A. Safe harbour statement: don't assume anything based on this presentation. Verify on your own. Errare humanum est.
7. How to stay up to date with Java • Communities, conferences • Your local JUG: https://dev.java/community/jugs/ and/or the VirtualJUG: https://www.meetup.com/virtualjug/ • The JEPs: https://openjdk.org/jeps/0 • Blogs, like: ◦ 󰐤 JVM Bloggers: https://jvm-bloggers.com/ ◦ IntelliJ IDEA: https://blog.jetbrains.com/idea/ ◦ Software Garden: https://softwaregarden.dev/ ◦ Inside Java: https://inside.java/ • and many, many more
14. Simple / Compact source files & Instance main methods 🧪 Preview in Java 24 JEP 495 Standard feature in Java 25 JEP 512
15. Simple / Compact source files & Instance main methods public class HelloWorld { public static void main(String[] args) { System.out.println("Witaj Świecie!"); } }
16. Simple / Compact source files & Instance main methods public class HelloWorld { public static void main(String[] args) { System.out.println("Witaj Świecie!"); } }
17. Simple / Compact source files & Instance main methods public class HelloWorld { public static void main(String[] args) { System.out.println("Witaj Świecie!"); } } void main() { println("Witaj Świecie!"); }
18. Preview features --enable-preview JEP 12 ▶
19. DEMO 2: Playing with Java 24
20. All these pictures are from pixabay.com Stunning royalty-free images & royalty-free stock
21. “an apple on books” Multimodal encoder
22. Multimodal encoder POST elasticsearch/catalogue { "filename" : "apple.png", "embedding" : [0.12, -0.48, 0.0231, …], … } Preparation: Indexing
23. Multimodal encoder POST ${elasticsearch}/catalogue/_search { } “apple” “apple” POST ${elasticsearch}/catalogue/_search { } RRF Results: 1. … 2. … 3. … 4. … Application: Searching ▶
24. Records Standard feature in Java 16 JEP 395 immutable transparent data carriers
25. 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 + ']'; } 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 + ']'; } }
26. Module imports 🧪 Preview in Java 24 JEP 494 Standard feature in Java 25 JEP 511 ▶
27. 🧪 Preview in Java 24 JEP 495 Standard feature in Java 25 JEP 512 Simple / Compact source files & Instance main methods ▶ Also comes with simple IO
28. Stream Gatherers Standard feature in Java 24 JEP 485
29. 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 ▶
30. Structured Concurrency 🧪 Preview in Java 24 JEP 499 🧪 Preview in Java 25 JEP 505
31. Structured Concurrency • better "idioms" for multi-threaded code • synchronous way of thinking • help eliminate thread leaks and cancellation delays
32. Task POST ${elasticsearch}/catalogue/_search { } “apple” POST ${elasticsearch}/catalogue/_search { } RRF Results: 1. … 2. … 3. … 4. … Structured Concurrency Subtask Subtask combine Results: 1. … ▶
33. static SearchResult executeSearch(QueryWithVector qwv, String indexName, ElasticsearchClient esClient) { try (var scope = new StructuredTaskScope.ShutdownOnFailure()) { var knnSearch = scope.fork(() -> performKnnSearch(qwv.vector(), indexName, esClient)); var classicSearch = scope.fork(() -> performClassicSearch(qwv.query(), indexName, esClient)); scope.join(); scope.throwIfFailed(); var combined = combineUsingRRF(List.of(knnSearch.get(), classicSearch.get()), 60, TOP_K); return new SearchResult(qwv.query(), combined); } catch (Exception e) { throw new RuntimeException(); } } static SearchResult executeSearch(QueryWithVector qwv, String indexName, ElasticsearchClient esClient) { try (var scope = StructuredTaskScope.open()) { var knnSearch = scope.fork(() -> performKnnSearch(qwv.vector(), indexName, esClient)); var classicSearch = scope.fork(() -> performClassicSearch(qwv.query(), indexName, esClient)); scope.join(); var combined = combineUsingRRF(List.of(knnSearch.get(), classicSearch.get()), 60, TOP_K); return new SearchResult(qwv.query(), combined); } catch (Exception e) { throw new RuntimeException(); } } Java 24 Java 25
34. TL;DR: .open() with Joiner and Config, can (re)use thread pools, also platform ones Structured Concurrency: Java 24 vs 25 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()); }
35. CompletableFuture has no future!
37. 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/ ▶
38. Stay up to date 1. pom.xml / gradle.kts 2. new idioms ▶
39. Pattern matching 🧪 Preview in Java 24 JEP 488 🧪 Preview in Java 25 JEP 507 • Allow primitive types in all pattern contexts • Extend instanceof and switch to work with all primitive types ▶
42. Vector API (Panama) 🧫 Incubator in Java 24 JEP 489 🧫 Incubator in Java 25 JEP 508 ▶
43. • API to express vector computations • Different performance characteristics ▶
45. $ 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 -Dlog4j.shutdownHookEnabled=false -Dlog4j2.disable.jmx=true -Dlog4j2.formatMsgNoLookups=true -Djava.locale.providers=CLDR -Dorg.apache.lucene.vectorization.upperJavaFeatureVersion=24 -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 -Des.entitlements.enabled=true -XX:+EnableDynamicAgentLoading -Djdk.attach.allowAttachSelf=true --patch-module=java.base=lib/entitlement-bridge/elasticsearch-entitlement-bridge-9.0.0.jar --add-exports=java.base/org.elasticsearch.entitlement.bridge=org.elasticsearch.entitlement,java.lo gging,java.net.http,java.naming,jdk.net -XX:+UseG1GC -Djava.io.tmpdir=/tmp/elasticsearch-11578202498973800384 --add-modules=jdk.incubator.vector -Dorg.apache.lucene.store.defaultReadAdvice=normal -XX:+HeapDumpOnOutOfMemoryError -XX:+ExitOnOutOfMemoryError -XX:HeapDumpPath=data -XX:ErrorFile=logs/hs_err_pid%p.log -Xlog:gc*,gc+age=trace,safepoint:file=logs/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 ▶
46. What did we play with? Vectors from Panama Records Structured Concurrency Stream Gatherers Pattern Matching Compact Classes, module imports, simple IO … and more
47. Each new Java version is: • easier • faster • better • and (guess what?) still free Why not use it?
50. How was it? bit.ly/LMJPW-DevoxxPL
51. The (QR) code & everything bit.ly/LMJPW-all
53. Thank you! Bedankt & Dziękuję Piotr Przybył @piotrprz @piotrprz.bsky.social Senior Developer Advocate Marit van Dijk @MaritvanDijk77 @maritvandijk.bsky.social Developer Advocate