Exploring JDK 25 RC: Key Features & First Impressions

// Old way: Using a thread pool for I/O tasks
ExecutorService executor = Executors.newFixedThreadPool(200);
for (int i = 0; i < 10_000; i++) {
    executor.submit(() -> {
        // Perform a blocking network call
        String result = makeNetworkCall(); 
        process(result);
    });
}

// New way with JDK 25: Simple, scalable, and readable
// 'newVirtualThreadPerTaskExecutor' is your new best friend!
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 10_000; i++) {
        executor.submit(() -> {
            // Write simple blocking code, the JVM handles the rest
            String result = makeNetworkCall();
            process(result);
        });
    }
} // executor.close() implicitly waits for all tasks to complete

“It simplifies multithreaded programming by treating groups of related tasks running in different threads as a single unit of work.”

Imagine fetching user data and order history simultaneously. With StructuredTaskScope, if fetching the user data fails, you can instantly cancel the order history fetch. This makes your code more robust and easier to reason about than the old world of scattered Future objects.

Beyond the JVM: A New Bridge to Native Code

For decades, when Java needed to talk to native libraries (like those written in C/C++), the answer was the Java Native Interface (JNI). While powerful, JNI is notoriously complex, error-prone, and unsafe. A small mistake in your C code or JNI glue could crash the entire JVM.

Enter the Foreign Function & Memory (FFM) API, which graduates from preview in JDK 25. This is the modern, safe, and pure-Java replacement for JNI. It provides a way to directly call native functions and safely access memory outside the Java heap, all from within your Java code.

Why is this a big deal?

• Safety: No more fragile C++ glue code. The FFM API operates within the safety net of the JVM.
• Simplicity: It’s a Java API. You don’t need a C++ compiler or a separate build process for your native bindings.
• Performance: It’s designed to be fast, often matching or even exceeding the performance of hand-rolled JNI.

While you might not use the FFM API directly in your day-to-day business logic, it's a massive win for the ecosystem. Libraries that rely on native code for performance (think machine learning, advanced graphics, or high-speed data processing) can now provide safer, more reliable integrations. This lowers the barrier to entry for using high-performance native libraries in the Java world.

Smarter, Safer Code with Advanced Pattern Matching

Java’s journey with Pattern Matching has been a fantastic evolution in making the language more expressive and less boilerplate-heavy. JDK 25 continues this trend by solidifying features that have been in preview, most notably Pattern Matching for `switch`.

This isn’t your grandparent’s `switch` statement. It’s a super-charged expression that can deconstruct objects, check types, and evaluate conditions in a clean, declarative way.

// Before: A clunky if-else-if chain
String format(Object obj) {
    if (obj instanceof Integer i) {
        return String.format("An integer: %d", i);
    } else if (obj instanceof Long l) {
        return String.format("A long: %d", l);
    } else if (obj instanceof Double d) {
        return String.format("A double: %.2f", d);
    } else if (obj instanceof String s) {
        return String.format("A string: %s", s);
    } else {
        return "Unknown object";
    }
}

// After with JDK 25: Expressive, safe, and beautiful
String format(Object obj) {
    return switch (obj) {
        case Integer i -> String.format("An integer: %d", i);
        case Long l    -> String.format("A long: %d", l);
        case Double d  -> String.format("A double: %.2f", d);
        case String s  -> String.format("A string: %s", s);
        default        -> "Unknown object";
    };
}

The real magic is compile-time safety. When switching over a sealed interface or an enum, the compiler will tell you if you've forgotten a case. This exhaustiveness checking eliminates a whole class of runtime bugs. It's a feature that, once you start using it, you'll wonder how you ever lived without.

What's on the Horizon?

A new JDK release isn’t just about finalized features; it’s also about what’s cooking. JDK 25 continues to incubate the Vector API, which allows developers to write complex vector calculations that are compiled at runtime to optimal vector instructions on the underlying CPU. It’s a powerful tool for AI, scientific computing, and any domain that requires crunching large amounts of numerical data.

We're also seeing previews of new language features like Scoped Values. These are a modern alternative to thread-local variables, designed to work seamlessly with virtual threads for sharing data within a bounded scope of execution, without the need to pass it through every method in a call stack. It’s a cleaner, more robust solution to a common problem.

Final Thoughts: Is JDK 25 a Must-Have?

After spending some time with the JDK 25 RC, the answer is a resounding yes. While it's not an LTS release, the features it finalizes are so foundational that they will shape Java development for the next decade.

The finalization of Virtual Threads and Structured Concurrency alone marks a new era for Java. It democratizes high-performance, concurrent programming, making it accessible to every developer. The FFM API modernizes Java's interaction with the native world, and the continued improvements to Pattern Matching make the core language more delightful to use.

JDK 25 feels less like a step and more like a leap. It delivers on promises made years ago, solidifying Java’s position as a modern, high-performance, and developer-friendly language. It’s time to download the RC, kick the tires, and get ready for the future of Java. It’s brighter than ever.