the runtime illusion: what Java really runs

Wed, 18 Feb 2026 07:00:02 +0000

Introduction

Java’s bytecode is made abstract to be portable and neutral from specific hardware. Yet in production, it performs with the precision of native code. How? The secret lies in the JIT compiler, a near magical blend of static analysis and real-time insights. It reinterprets, restructures and often reinvents the code based on the runtime behaviour. This article traces that silent transformation using the Semeru (OpenJ9) JIT, following a method from source to bytecode to intermediate representation and ultimately to highly optimised machine code. You will be amazed to see how your logic is optimized beyond recognition. What you write is not always what runs, and what runs is often much better version of what you imagined.

IBM Architect Mark Stoodley Reveals JVM Optimization Techniques

Wed, 07 May 2025 10:17:14 +0000

Slow Java startups, repeated JIT compilations, high CPU load: these factors are not just performance issues — they also drive up infrastructure costs and increase the energy consumption of applications. At JCON EUROPE 2025, developers will have a rare opportunity: Mark Stoodley, Chief Architect for Java at IBM, travels from Canada to personally lead an exclusive workshop. The title: “Ultra Efficient Startup for Production Java Workloads” — a hands-on format demonstrating how to run JVM-based production applications more efficiently, faster, and with lower resource consumption.

JIT on JAVAPRO International

the runtime illusion: what Java really runs

Introduction

IBM Architect Mark Stoodley Reveals JVM Optimization Techniques