Java

Inside JDK 25: Features, Fixes, and Future of Java

JDK 25

Author: Shiva Srivastava
Reviewed by: Shramik Masti
Published on: May 29, 2025

Three Months to Go — here’s the lowdown

JDK 25 is dropping this September, and it’s packed with serious upgrades that will transform how you write Java code. Among the headline features are Scoped Values for safer concurrency, improved performance with Compact Object Headers, and enhanced concurrency tools that boost scalability and maintainability.

On the security front, JDK 25 finalizes the much-anticipated Key Derivation Function (KDF) API introduced as a preview in JDK 24. This critical addition fills a major gap in Java's cryptographic toolkit – existing APIs like KeyGenerator and SecretKeyFactory were never designed for modern key derivation scenarios where multiple parties need to deterministically generate identical keys from shared inputs. The new KDF API enables secure multi-key derivation using standards like HKDF, provides essential building blocks for quantum-safe encryption schemes like HPKE, and paves the way for post-quantum cryptography as classical methods become vulnerable to quantum computing attacks.

JDK 25 also brings a highly requested language improvement: Flexible Constructor Bodies. This feature removes the long-standing restriction that constructor invocations (super(...) or this(...)) must be the very first statement. Now, you can place safe initialization code and validations before calling the superclass constructor. This allows for more natural and safer object construction patterns, like validating arguments early to fail fast without unnecessary work.

If you care about building scalable, maintainable, and secure systems — while writing cleaner, more intuitive code — JDK 25 is definitely worth your attention.

Feature Status Guide:
Incubator = Experimental API
Preview = Near-final testing
Final = Production-ready
LTS = Long-Term Support

Java 25 isn't just another release—it's the next Long Term Support (LTS) version after Java 21, scheduled for September 16, 2025. If you're still using Java 8, 11, or even 17, this is your next major upgrade target.

Key highlights:

Thread-safe data sharing without ThreadLocal headaches
Simplified concurrent programming that actually makes sense
Enhanced startup performance and memory optimization
Modern cryptography and pattern matching improvements

1. Scoped Values (JEP 487 - Final)

What it solves: Ever struggled with ThreadLocal variables leaking memory or being hard to manage? Scoped Values fix this completely.

Real-world example:

// Old way with ThreadLocal (problematic)
private static final ThreadLocal<String> USER_ID = new ThreadLocal<>();

// New way with Scoped Values (clean & safe)
private static final ScopedValue<String> USER_ID = ScopedValue.newInstance();

public void handleRequest(String userId) {
    ScopedValue.where(USER_ID, userId).run(() -> {
        // Any method called here can access USER_ID.get()
        processOrder();
        sendNotification();
        logActivity();
        // Value automatically cleaned up when this block ends
    });
}

Immutable by design - no accidental modifications
Automatic cleanup - no memory leaks
Virtual thread optimized - perfect for modern Java
Type-safe - compile-time safety

2. Structured Concurrency (JEP 506 - Fifth Preview)

What it solves: Tired of complex ExecutorService code that's hard to debug? Structured Concurrency groups related tasks as a single unit.

Before & After comparison:

// Before: Complex ExecutorService code
ExecutorService executor = Executors.newCachedThreadPool();
try {
    Future<UserData> userData = executor.submit(() -> fetchUser(userId));
    Future<List<Order>> orders = executor.submit(() -> fetchOrders(userId));
    
    // Complex error handling and cleanup...
    UserData user = userData.get(5, TimeUnit.SECONDS);
    List<Order> orderList = orders.get(5, TimeUnit.SECONDS);
    
} finally {
    executor.shutdown();
}

// After: Clean Structured Concurrency
try (var scope = StructuredTaskScope.open()) {
    var userData = scope.fork(() -> fetchUser(userId));
    var orders = scope.fork(() -> fetchOrders(userId));
    
    scope.join(); // Wait for all tasks
    
    return new UserProfile(userData.resultNow(), orders.resultNow());
}

Easier debugging - clear parent-child task relationships
Automatic cancellation - if one fails, others stop
Better observability - thread dumps show task hierarchy
Simpler error handling - exceptions propagate naturally

3. Compact Object Headers: Significant Memory Optimization (JEP 501 - Production Ready)

What changed: Object headers shrunk from 128 bits to 64 bits on 64-bit systems.

Impact on your applications:

# Enable compact headers in production
java -XX:+UseCompactObjectHeaders YourApp

# Results from real benchmarks:
# 22% less heap memory usage
# 8% faster CPU performance  
# 15% fewer garbage collections

Perfect for:

Microservices with memory constraints
Cloud deployments where memory equals cost
Applications with millions of small objects
Enterprise apps optimizing for efficiency

4. AOT (Ahead-of-Time) Improvements: Enhanced Startup Performance

Two major AOT enhancements deliver substantial startup improvements:

JEP 514 - Simplified AOT Commands:

# Old way (2 steps)
java -XX:AOTMode=record -XX:AOTConfiguration=app.conf MyApp
java -XX:AOTMode=create -XX:AOTConfiguration=app.conf -XX:AOTCache=app.aot

# New way (1 step)
java -XX:AOTCacheOutput=app.aot MyApp

# Use the cache for faster startup
java -XX:AOTCache=app.aot MyApp

JEP 515 - Method Profiling:
AOT now remembers which methods are "hot" during training, so production apps reach peak performance immediately instead of warming up.

5. Module Import Declarations: Reduce Import Boilerplate (JEP 508 - Second Preview)

Problem: Importing multiple classes from the same module is verbose.

Solution:

// Before: Multiple imports
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import java.nio.file.Path;
import java.nio.file.Files;

// After: Single module import
import module java.base;  // Imports all 54 packages!

// Now use any class from java.base module
List<String> items = List.of("a", "b", "c");
Map<String, Integer> counts = items.stream()
    .collect(Collectors.groupingBy(s -> s, Collectors.summingInt(s -> 1)));

6. Vector API: High-Performance Computing (JEP 506 - Tenth Incubator)

Perfect for: AI/ML workloads, financial calculations, image processing.

Example:

// Process 8-16 numbers at once instead of one-by-one
static final VectorSpecies<Float> SPECIES = FloatVector.SPECIES_PREFERRED;

void vectorizedCalculation(float[] a, float[] b, float[] result) {
    for (int i = 0; i < SPECIES.loopBound(a.length); i += SPECIES.length()) {
        var va = FloatVector.fromArray(SPECIES, a, i);
        var vb = FloatVector.fromArray(SPECIES, b, i);
        
        // Calculate (a² + b²) for 8-16 numbers simultaneously
        var result_vector = va.mul(va).add(vb.mul(vb));
        result_vector.intoArray(result, i);
    }
}

Performance gains:

2-16x faster than regular loops
Automatic optimization for your CPU (AVX, NEON, etc.)
Easy to use - just change your loops

7. Key Derivation Function API: Modern Cryptography (JEP 510)

What is it? Standardized API in javax.crypto.KDF for secure key generation supporting TLS 1.3, HPKE, and post-quantum cryptography.

Real-world use cases:

Secure password hashing and encryption key generation
Generating entropy for secure communication protocols
Interfacing with hardware-backed security modules

// Example: Deriving a 256-bit AES key using PBKDF2
public SecretKey deriveKeyFromPassword(char[] password, byte[] salt) throws Exception {
    KDF kdf = KDF.getInstance("PBKDF2");
    kdf.init(new PBKDF2ParameterSpec(salt, 210000, "HmacSHA256"));
    return kdf.deriveKey(
        new SecretKeySpec(new String(password).getBytes(), "RAW"),
        "AES",
        256,
        null
    );
}

8. Primitive Types in Patterns: Safe Type Conversions (JEP 507 - Third Preview)

Enhanced pattern matching that allows primitive types in all pattern contexts and extends switch to work with all primitive types.

// Safe primitive type patterns
int i = 1000;
if (i instanceof byte b) {
    processAsByte(b);  // Only executes if conversion is safe
}

// Enhanced switch with all primitive types
switch (sensor.getTemperature()) {
    case 0.0f -> "freezing";
    case float temp when temp > 100.0f -> "boiling";
    case float temp when temp < 0.0f -> "below freezing";
    case float temp -> "normal: " + temp + "°C";
}

Developer experience improvement:

Eliminates unsafe casts and manual range checks
Provides compile-time safety for primitive conversions
Makes pattern matching work seamlessly with all types

9. Flexible Constructor Bodies: Simplified Object Initialization (JEP 513)

What are Flexible Constructor Bodies? This feature relaxes the requirement that constructor calls to this() or super() must be the first statement.

Real-world use case: Object construction that requires preparation before parent initialization.

// Before Java 25 - Awkward workarounds needed
class ConfigurableService extends BaseService {
    ConfigurableService(String configPath) {
        // Had to use static method or duplicate code
        super(loadConfig(configPath).getServiceName());
        // More initialization here...
    }
    
    private static Config loadConfig(String path) {
        // Duplicate code needed just for constructor
        return new ConfigParser().parse(path);
    }
}

// With Java 25's flexible constructor bodies
class ConfigurableService extends BaseService {
    ConfigurableService(String configPath) {
        // Prepare everything we need first
        var parser = new ConfigParser();
        var config = parser.parse(configPath);
        var loggingLevel = determineLogLevel(config);
        
        // Call super with prepared values
        super(config.getServiceName());
        
        // Continue initialization
        this.configure(config);
        initLogging(loggingLevel);
    }
}

Code quality improvement: Leads to more logical, readable constructor code with less duplication and fewer helper methods.

10. Stable Values (JEP 502 – Preview)

What are Stable Values? A new API that enables deferred immutability — values are initialized lazily, safely, and at most once, even in multithreaded environments.

Why it matters: Traditionally, final fields must be initialized eagerly. Mutable fields offer flexibility but at the cost of safety and performance. Stable values strike the perfect balance: delayed initialization with immutability and constant-folding optimizations by the JVM.

Real-world use cases:

Loading configuration or logger instances only when needed
Creating shared resources (e.g., database config, caches) on demand
Improving application startup time by deferring unnecessary initialization

// Define a stable value for expensive database configuration
private static final StableValue<DbConfig> DB_CONFIG = 
    StableValue.of(() -> {
        System.out.println("Loading DB config (happens only once)");
        return loadDatabaseConfig();
    });

// Use it across multiple threads without synchronization concerns
public Connection getConnection() throws SQLException {
    DbConfig config = DB_CONFIG.get(); // Only computed first time
    return DriverManager.getConnection(
        config.url(), config.username(), config.password());
}

What's new in JDK 25:

A preview API StableValue<T> that guarantees single-time, thread-safe initialization
Support for constant folding after initialization
Cleaner replacement for double-checked locking and lazy singletons

Performance impact: Removes manual synchronization overhead and enables better startup time and runtime efficiency without sacrificing thread safety.

11. Compact Source Files & Instance Main Methods (JEP 512)

What are Compact Source Files? A streamlined syntax that eliminates class declarations and allows instance main methods, making Java programs more concise and beginner-friendly.

Real-world use case: Educational programming, command-line utilities, prototyping, and small scripts.

// Before Java 25 - Traditional Hello World
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

// Java 25 - Instance main method (simplified)
class HelloWorld {
    void main() {
        System.out.println("Hello, World!");
    }
}

// Java 25 - Compact source file (no class needed!)
void main() {
    IO.println("Hello, World!");
}

Key Features:

// Complete compact source file with methods and fields
String greeting = "Hello, Java 25!";

String getWelcomeMessage() {
    return greeting + " Welcome to compact source files!";
}

void main() {
    String name = IO.readln("Please enter your name: ");
    IO.print("Pleased to meet you, ");
    IO.println(name);
    IO.println(getWelcomeMessage());
}

// Automatic imports from java.base module - no import statements needed!
// List, Map, Stream, Path, Files, etc. are all available
void processData() {
    var authors = List.of("James", "Bill", "Guy", "Alex", "Dan", "Gavin");
    for (var name : authors) {
        IO.println(name + ": " + name.length());
    }
}

Dramatically reduces boilerplate for small programs, provides smooth learning curve from simple scripts to complex applications, includes built-in console I/O with IO class, and automatically imports essential Java classes without ceremony.

Additional Features in Java 25

Also coming in Java 25:

32-bit x86 Removal - Focus on modern platforms
JFR Enhancements - Better production debugging
Generational Shenandoah GC - Lower pause times

Performance Improvements That Matter

Memory & Startup Benchmarks

Metric	Java 21	Java 25	Improvement
Startup Time	2.5s	1.2s	52% faster
Memory Usage	100MB	78MB	22% reduction
Vector Operations	1x	2-16x	Up to 16x faster
GC Frequency	Baseline	-15%	Fewer pauses

Conclusion

Java 25 represents the biggest leap in Java performance and developer experience since Java 17. The combination of Scoped Values and Structured Concurrency finally makes concurrent Java programming intuitive, while Compact Object Headers deliver immediate cost savings for cloud deployments.

With enhanced cryptography support, improved pattern matching, and significant performance optimizations, Java 25 LTS transforms how developers write modern Java applications.

Bottom line: If you're planning your next Java upgrade, Java 25 LTS should be at the top of your list.

Download Java 25 Preview

Early Access Downloads:

OpenJDK 25 Early Access Builds - Official Oracle OpenJDK builds
Oracle JDK 25 Early Access - Oracle commercial builds
Eclipse Temurin 25 EA - Adoptium community builds

References

https://openjdk.org/jeps/487
https://openjdk.org/jeps/506
https://openjdk.org/jeps/501
https://openjdk.org/jeps/514
https://openjdk.org/jeps/515
https://openjdk.org/jeps/508
https://openjdk.org/jeps/506
https://openjdk.org/jeps/510
https://openjdk.org/jeps/507
https://www.oracle.com/java/technologies/javase/25-relnotes.html
https://openjdk.org/projects/jdk/25/
https://blogs.oracle.com/java/