Stop Saying Java is Slow

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How goes the battle?

Java 25 Performance: Faster Starts, Smarter Memory, Better GC

Java 25 isn’t just another incremental release. It brings meaningful performance improvements that directly impact how fast your applications start, how much memory they consume, and how efficiently they manage garbage collection.

Let’s break down what changed, and why it matters.

🚀 Faster Startup with the New AOT Cache

One of the most exciting additions in Java 25 is the new Ahead-of-Time (AOT) cache.

Traditionally, when a Java application starts, the Just-In-Time (JIT) compiler kicks in and begins optimizing code as it runs. While this leads to excellent long-term performance, it adds overhead during startup.

Java 25 changes that.

With the AOT cache (introduced through JEPs 483 and 514), you can perform a “training run” of your application. During this run, the JVM observes which classes and methods are actually used. It then generates an optimized cache specifically for that execution profile.

Later, when the application starts in production, the JVM loads this prebuilt cache directly into memory. The result? Much less JIT work at startup, and dramatically faster boot times.
In large applications with many classes, startup times can improve by up to 50%.
And it gets better.
JEP 515 enhances the AOT cache by incorporating profiling data collected by the JIT itself. That means the cache isn’t just precompiled, it’s optimized based on real runtime behavior. Smarter data, better performance.

JEP 483

JEP 514

JEP 515

🧠 Smaller Object Headers, Lower Memory Usage

Java 25 also takes aim at memory efficiency with Compact Object Headers (JEP 519).

Every object in Java carries a header containing metadata used by the JVM. While small individually, these headers add up quickly in systems managing millions of objects.
Java 25 optimizes and reduces the size of these headers, decreasing overall memory footprint.

Why does this matter?

Applications consume less memory
The Garbage Collector has less work to do
Performance improves under memory pressure

In extensive production testing across hundreds of services, memory usage dropped by up to 20% in some workloads. Processing time improved by up to 10%, and GC cycles were up to 15% less frequent.

That’s not theoretical, that’s production-grade validation.

JEP 450

JEP 519

♻️ Garbage Collection Keeps Evolving

Java has always offered multiple garbage collectors for different workloads. In Java 25, all major collectors receive meaningful upgrades.

Shenandoah Goes Generational

Shenandoah is known for low-latency performance, minimizing pause times by performing most of its work concurrently with the application.

With JEP 521, Shenandoah now supports a generational mode. Generational GC typically performs better because most objects die young — and now Shenandoah can take advantage of that reality.

ZGC Embraces Generational Design

ZGC also moves forward with a generational implementation (JEP 474). In fact, the non-generational mode has been deprecated. Since generational approaches generally provide better performance characteristics, future innovation will focus there.

G1 Gets Smarter About JNI

G1, still the default GC in Java 25, also improves through JEP 423. The focus here is reducing pause times during operations involving JNI (Java Native Interface).

For applications interacting with native code, this means smoother performance and fewer unexpected delays.

JEP 423

JEP 474

JEP 521

The Big Picture

Java 25 isn’t flashy, it’s practical.

Faster startup with AOT caching
Lower memory usage with compact object headers
Smarter, more efficient garbage collection

These aren’t cosmetic changes. They directly impact cloud deployments, containerized applications, microservices, and large enterprise systems.

Modern Java keeps evolving, and it’s becoming faster, leaner, and more production-optimized with every release.

Picture 01: Duke speedster inspired

Java 25 represents a major leap forward in making the JVM more efficient and developer-friendly than ever before. With the new AOT caching system dramatically slashing startup times (up to 50% in many cases), Compact Object Headers shrinking memory usage by up to 20%, and meaningful refinements to G1, ZGC, and Shenandoah, the platform is now faster to launch, lighter on resources, and more responsive under load, all while maintaining the reliability and scalability Java is known for. Whether you’re building cloud-native microservices, real-time applications, or large-scale enterprise systems, these improvements mean less waiting, lower costs, and smoother performance right out of the gate. Java 25 isn’t just an incremental update, it’s a clear signal that the language continues to evolve to meet modern demands. Time to upgrade and experience the difference yourself!