The second feature, late barrier expansion for the G1 garbage collector, is intended to simplify the implementation of G1’s barriers. The G1 garbage collector’s barriers record information about application memory accesses, by shifting their expansion from early in the C2 compilation pipeline to later. 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.
A third feature, 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.
Additional features targeting JDK 24 will be determined during the next several months. Potential Java 24 features include further previews or final releases of features being previewed in JDK 23. These include stream gatherers, to enhance the stream API for custom intermediate operations; module import declarations, for succinctly importing all packages exported by a module and simplifying reuse of modular libraries; structured concurrency, to simplify concurrent programming; scoped values, for sharing immutable data; and flexible constructor bodies, giving developers greater freedom to express behavior of constructors.
