Java bytecode is created by the compiler and interpreted by the JVM, but that is just a part of the truth. It is also generated, analyzed, manipulated, and instrumented during build and run time by various tools, frameworks, and libraries. That plays well into Java’s dynamism but also has downsides, a big one being that manipulating bytecode can only be done reliably by libraries that were released after the Java version, for which the bytecode was compiled. As a consequence a Java update often requires updating a considerable portion of the a project’s dependencies.

The new class-file API that Brian Goetz presented at JVMLS in august 2023 will improve that situation greatly by shipping an always up-to-date bytecode anlysis and manipulation API with the JDK.

Make sure to check the show-notes.