Learning modern Java the playful way (Devoxx PL)

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Learning modern Java the playful way Marit van Dijk, Piotr Przybył Devoxx PL MMXXV

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$ who are we Piotr Przybył @piotrprz @piotrprz.bsky.social Senior Developer Advocate Marit van Dijk @MaritvanDijk77 @maritvandijk.bsky.social Developer Advocate

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$ who are you

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Agenda ● Various features from recent Java versions (not all of them, obviously) ● Demos (obviously)

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CAVEAT AVDITORES A.K.A. Safe harbour statement: don't assume anything based on this presentation. Verify on your own. Errare humanum est.

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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

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Simple / Compact source files & Instance main methods 🧪 Preview in Java 24 JEP 495 Standard feature in Java 25 JEP 512

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Simple / Compact source files & Instance main methods public class HelloWorld { public static void main(String[] args) { System.out.println("Witaj Świecie!"); } }

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Simple / Compact source files & Instance main methods public class HelloWorld { public static void main(String[] args) { System.out.println("Witaj Świecie!"); } }

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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!"); }

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Preview features --enable-preview JEP 12 ▶

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DEMO 2: Playing with Java 24

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All these pictures are from pixabay.com Stunning royalty-free images & royalty-free stock

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“an apple on books” Multimodal encoder

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Multimodal encoder POST elasticsearch/catalogue { "filename" : "apple.png", "embedding" : [0.12, -0.48, 0.0231, …], … } Preparation: Indexing

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Multimodal encoder POST ${elasticsearch}/catalogue/_search { } “apple” “apple” POST ${elasticsearch}/catalogue/_search { } RRF Results: 1. … 2. … 3. … 4. … Application: Searching ▶

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Records Standard feature in Java 16 JEP 395 immutable transparent data carriers

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final class QueryWithVector { private final String query; private final List vector; QueryWithVector(String query, List vector) { this.query = query; this.vector = vector; } @Override public String toString() { return "QueryWithVector[" + "query=" + query + ", " + "vector=" + vector + ']'; } public String getQuery() { return query; } public List 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 vector) { @Override public String toString() { return "QueryWithVector[" + "query=" + query + ", " + "vector=" + vector + ']'; } }

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Module imports 🧪 Preview in Java 24 JEP 494 Standard feature in Java 25 JEP 511 ▶

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🧪 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

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Stream Gatherers Standard feature in Java 24 JEP 485

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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 ▶

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Structured Concurrency 🧪 Preview in Java 24 JEP 499 🧪 Preview in Java 25 JEP 505

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Structured Concurrency ● better "idioms" for multi-threaded code ● synchronous way of thinking ● help eliminate thread leaks and cancellation delays

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Task POST ${elasticsearch}/catalogue/_search { } “apple” POST ${elasticsearch}/catalogue/_search { } RRF Results: 1. … 2. … 3. … 4. … Structured Concurrency Subtask Subtask combine Results: 1. … ▶

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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

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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()); }

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CompletableFuture has no future!

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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/ ▶

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Stay up to date 1. pom.xml / gradle.kts 2. new idioms ▶

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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 ▶

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Vector API (Panama) 🧫 Incubator in Java 24 JEP 489 🧫 Incubator in Java 25 JEP 508 ▶

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● API to express vector computations ● Different performance characteristics ▶

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$ 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 ▶

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What did we play with? Vectors from Panama Records Structured Concurrency Stream Gatherers Pattern Matching Compact Classes, module imports, simple IO … and more

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Each new Java version is: ● easier ● faster ● better ● and (guess what?) still free Why not use it?

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How was it? bit.ly/LMJPW-DevoxxPL

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The (QR) code & everything bit.ly/LMJPW-all

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Thank you! Bedankt & Dziękuję Piotr Przybył @piotrprz @piotrprz.bsky.social Senior Developer Advocate Marit van Dijk @MaritvanDijk77 @maritvandijk.bsky.social Developer Advocate