Teaching an Old Handle New Tricks: From Core Reflection to FFM

Core reflection has been a cornerstone of Java since Java SE 1.1. It provides a unified model for inspecting classes, invoking methods and accessing fields. But reflection is also inefficient. Every reflective call must check access, handle argument conversions like boxing and, finally, invoke the target.

Method handles, introduced in Java 7, address this problem with an execution model that closely mirrors the JVM's. A method handle is one resolved executable operation: a typed capability whose access rights and type are established up front. In Java 9, var handles extended this model to fields and array elements.

In this talk, we’ll show how this trick—moving expensive, one-off setup work out of the hot path—has paid dividends across the Java platform. Method and var handles now sit at the core of many modern runtime features, making string concatenation more efficient, revolutionizing native interop with the Foreign Function & Memory API, and enabling serialization to be redesigned on safer foundations.

This is both an advanced tour of an overlooked part of the Java runtime and a story of resilient platform design: how the right hammer keeps finding new nails.