☕ Java 26 Feature Demos

A collection of runnable demos showcasing new features in JDK 26 (released March 2026). Each demo is a self-contained Java class with extensive Javadoc documentation explaining the feature, its motivation, and usage patterns.

📋 Prerequisites

Requirement	Version
JDK	26 (EA or GA)
Maven	3.9+

Verify your setup:

java -version   # Should show "26" or "26-ea"
mvn --version   # Should show 3.9+

🔨 Build

mvn compile

The project is pre-configured with --enable-preview and --add-modules jdk.incubator.vector in pom.xml.

🚀 Running Demos

Run any demo with:

java --enable-preview --add-modules jdk.incubator.vector \
  -cp target/classes <fully.qualified.ClassName>

Or using Maven:

mvn compile exec:exec -Dexec.mainClass=<fully.qualified.ClassName>

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📚 Feature Index

✅ Standard Features (Final)

#	JEP	Feature	Demo Class	Description
1	JEP 517	HTTP/3 for the HTTP Client API	o.e.standard.Http3Demo	HttpClient now supports HTTP/3 (QUIC)
6	JEP 500	Prepare to Make Final Mean Final	o.e.standard.FinalFieldWarningsDemo	Runtime warnings when reflection mutates final fields

🔬 Preview Features (require --enable-preview)

#	JEP	Feature	Demo Class	Description
2	JEP 530	Primitive Types in Patterns	o.e.preview.PrimitivePatternsDemo	Pattern match on int, double, boolean in switch
3	JEP 525	Structured Concurrency	o.e.standard.StructuredConcurrencyDemo	Fork/join concurrent tasks as a unit of work
4	JEP 524	PEM Encodings of Crypto Objects	o.e.preview.PemEncodingDemo	Read/write PEM-encoded keys and certificates natively

🧪 Incubator Features (require --add-modules)

#	JEP	Feature	Demo Class	Description
5	JEP 529	Vector API	o.e.incubator.VectorApiDemo	SIMD computations via jdk.incubator.vector

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🔍 Detailed Feature Descriptions

1. JEP 517 — HTTP/3 for the HTTP Client API

java --enable-preview --add-modules jdk.incubator.vector \
  -cp target/classes org.example.standard.Http3Demo

What changed: The built-in java.net.http.HttpClient now supports HTTP/3 (RFC 9114), which runs over QUIC (RFC 9000) instead of TCP. HTTP/3 eliminates head-of-line blocking, achieves faster connection setup (0-RTT/1-RTT), and supports connection migration across networks.

The client transparently upgrades to HTTP/3 when a server supports it:

HttpClient client = HttpClient.newBuilder()
    .version(HttpClient.Version.HTTP_3)
    .build();
HttpResponse<String> resp = client.send(request, BodyHandlers.ofString());
resp.version()  // → HTTP_3

The demo covers: version enumeration, basic HTTP/3 requests, version negotiation comparison, async requests, and concurrent multiplexed requests.

Best for: High-performance API clients, CDN integration, mobile backends, microservice communication.

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2. JEP 530 — Primitive Types in Patterns

java --enable-preview --add-modules jdk.incubator.vector \
  -cp target/classes org.example.preview.PrimitivePatternsDemo

What changed: Pattern matching now supports primitive types in switch, instanceof, and record patterns:

switch (value) {
    case int i when i > 0  -> "positive int"
    case int i when i == 0 -> "zero"
    case int i             -> "negative int"
}

The demo covers: primitive switch on Object, guarded primitive patterns, record destructuring with primitives, narrowing conversions, and exhaustive boolean switch.

Status: Fourth Preview — requires --enable-preview.

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3. JEP 525 — Structured Concurrency

java --enable-preview --add-modules jdk.incubator.vector \
  -cp target/classes org.example.standard.StructuredConcurrencyDemo

What changed: StructuredTaskScope treats groups of concurrent tasks as a single unit:

try (var scope = StructuredTaskScope.open()) {
    var user  = scope.fork(() -> fetchUser());
    var order = scope.fork(() -> fetchOrder());
    scope.join();         // Wait for all
    use(user.get(), order.get());
}   // All tasks guaranteed complete here

Key joiners: awaitAll(), awaitAllSuccessfulOrThrow(), allSuccessfulOrThrow(), anySuccessfulOrThrow(), allUntil(Predicate).

Status: Sixth Preview — requires --enable-preview.

Best for: Concurrent service calls, fan-out/fan-in, replacing ExecutorService.

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4. JEP 524 — PEM Encodings of Cryptographic Objects

java --enable-preview --add-modules jdk.incubator.vector \
  -cp target/classes org.example.preview.PemEncodingDemo

What changed: Java now has a built-in API for encoding and decoding cryptographic objects in PEM format — the ubiquitous text format used by OpenSSL, SSH, TLS, and every crypto tool. No more manual Base64 wrapping or Bouncy Castle dependency.

PEMEncoder encoder = PEMEncoder.of();
String pem = encoder.encodeToString(publicKey);
// → "-----BEGIN PUBLIC KEY-----\nMIIBI..."

PEMDecoder decoder = PEMDecoder.of();
PublicKey key = decoder.decode(pem, PublicKey.class);

The demo covers: encoding public/private keys to PEM, round-trip verification, PEM record for raw access, and multi-object PEM bundles.

Status: Second Preview — requires --enable-preview.

Best for: Key export/import, certificate management, cross-platform crypto, CI/CD signing.

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5. JEP 529 — Vector API

java --enable-preview --add-modules jdk.incubator.vector \
  -cp target/classes org.example.incubator.VectorApiDemo

What changed: The Vector API enables SIMD (Single Instruction, Multiple Data) parallel computation on arrays. Process 4–16 elements per CPU instruction instead of one.

The demo covers: element-wise operations, reductions, conditional/masked operations, dot products, and a scalar-vs-SIMD comparison.

Status: Incubator (11th round) — requires --add-modules jdk.incubator.vector.

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6. JEP 500 — Prepare to Make Final Mean Final

java --enable-preview --add-modules jdk.incubator.vector \
  -cp target/classes org.example.standard.FinalFieldWarningsDemo

What changed: JDK 26 now issues runtime warnings when code uses reflection (java.lang.reflect) to mutate fields declared as final. This is the first step toward making final truly immutable — in a future JDK, these mutations will be blocked with an IllegalAccessException.

class UserProfile {
    private final String name = "Alice";
}

// This now triggers a WARNING in JDK 26:
Field f = UserProfile.class.getDeclaredField("name");
f.setAccessible(true);
f.set(profile, "Bob");  // ⚠️ WARNING: final field was set via reflection

The demo covers: final instance field mutation warnings, final static field warnings, reading final fields (still safe), non-final fields (unaffected), and proper migration alternatives (builders, records, constructor injection).

Best for: Understanding migration paths for frameworks (Jackson, Spring, Gson) that mutate final fields via reflection.

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📝 Non-Codeable JEPs in JDK 26

These JEPs are important but don't have runnable demo code in this project:

JEP	Feature	Why Not Codeable
JEP 504	Remove the Applet API	The java.applet package is removed entirely — there is no API left to call or demonstrate.
JEP 516	Ahead-of-Time Object Caching with Any GC	Controlled via JVM flags (-XX:AOTCache), not Java code. No programmatic API.
JEP 522	G1 GC: Improve Throughput by Reducing Synchronization	Internal JVM optimization — zero API surface, only observable via benchmarks.
JEP 526	Stable Values (Second Preview)	StableValue API is codeable in principle (real preview API), but not yet available in JDK 26 EA builds. Demos will be added once the API ships in a later EA or GA build.

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📁 Project Structure

java26/
├── pom.xml                                    # Maven config (Java 26 + preview + incubator)
├── README.md                                  # This file
└── src/main/java/org/example/
    ├── Main.java                              # Original hello-world
    ├── standard/                              # Final/standard features
    │   ├── Http3Demo.java                     # JEP 517
    │   ├── Http3RealWorldExamples.java        # JEP 517 real-world
    │   ├── FinalFieldWarningsDemo.java        # JEP 500
    │   ├── FinalFieldWarningsRealWorldExamples.java  # JEP 500 real-world
    │   ├── StructuredConcurrencyDemo.java     # JEP 525
    │   └── StructuredConcurrencyRealWorldExamples.java  # JEP 525 real-world
    ├── preview/                               # Preview features
    │   ├── PrimitivePatternsDemo.java         # JEP 530
    │   ├── PrimitivePatternsRealWorldExamples.java  # JEP 530 real-world
    │   ├── PemEncodingDemo.java               # JEP 524
    │   └── PemEncodingRealWorldExamples.java  # JEP 524 real-world
    └── incubator/                             # Incubator features
        ├── VectorApiDemo.java                 # JEP 529
        └── VectorApiRealWorldExamples.java    # JEP 529 real-world

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📜 License

This project is for educational purposes. Feel free to use, modify, and share.