JDK 24: The new features in Java 24

The vector API is designed to express vector communications that reliably compile at runtime to optimal vector instructions on supported CPU architectures, thus achieving performance superior to equivalent scalar computations. The vector API previously was incubated in JDK 16 through JDK 23. Goals of the proposal include clearly and concisely expressing a wide range of vector computations in an API that is platform-agnostic, that offers reliable runtime compilation and performance on x64 and AArch54 architectures, that degrades gracefully and still functions when a vector computation cannot be expressed at runtime, and that aligns with Project Valhalla, leveraging enhancements to the Java object model.

The class-file API, previously previewed in JDK 22 and JDK 23, would be finalized in JDK 24, with minor changes. This API provides a standard API for parsing, generating, and transforming Java class files. It aims to provide an API for processing class files that tracks the class file format defined by the Java Virtual Machine specification. A second goal is to enable JDK components to migrate to the standard API, and eventually remove the JDK’s internal copy of the third-party ASM library. Changes since the second preview include a renaming of enum values, removal of some fields, the addition of methods and method overloads, methods renamed, and removal of interfaces and methods deemed unnecessary.

Late barrier expansion for the G1 garbage collector is intended to simplify the implementation of G1’s barriers by shifting their expansion from early in the C2 compilation pipeline to later. The barriers record information about application memory accesses. Goals include reducing the execution time of C2 compilation when using the G1 collector, making G1 barriers comprehensible to HotSpot developers who lack a deep understanding of C2, and guaranteeing that C2 preserves invariants about the relative ordering of memory accesses, safepoints, and barriers. A fourth feature is preserving the quality of C2-generated JIT (just-in-time)-compiled code, in terms of speed and size.