Java 18 is still five months away but is already taking shape, with six feature proposals anticipated for it so far, the latest being a simple web server and a re-incubation of a foreign function and memory API.
The OpenJDK page for Java Development Kit (JDK) 18 lists the simple web server as proposed to target JDK 18 while a vector API, code snippets, and the UTF-8 charset officially target JDK 18 as of October 13. The JEP (JDK Enhancement Proposal) index of Java technologies also cites the record patterns and array patterns proposal as eyed for JDK 18, although it has not been officially targeted yet. A second incubation of a foreign function and memory API, which was incubated in Java 17, also is eyed for Java 18.
While JDK 17, published September 14, was a long-term support (LTS) release that will receive at least eight years of support from Oracle, JDK 18, expected in March 2022, will be a short-term feature release that is supported for six months. Early-access builds of JDK 18 can be found for Linux, Windows, and MacOS at java.net.
Specifics of the JDK 18 proposals include:
- With the simple web server proposal, a command-line tool would be provided to start a minimal web server that serves static files only. No CGI or servlet-like functionality is available. The tool will be useful for prototyping, ad-hoc coding, and testing, particularly in educational contexts. Goals of the plan include offering an out-of-the-box static HTTP file server with easy setup and minimal functionality, reducing developer activation energy and making the JDK more approachable, and providing a default implementation via the command line together with a small API for programmatic creation and customization. Providing a feature-rich or commercial-grade server is not a goal of the proposal.
- Foreign function and memory API, in which an API is introduced through which Java programs can interoperate with code and data outside of the Java runtime. By invoking foreign functions – code outside the JVM – and by safely accessing foreign memory – memory not managed by the JVM – the API lets Java programs call native libraries and process native data without the brittleness and danger of JNI (Java Native Interface). The intent is to replace JNI with a superior, pure Java development model. For JDK 18, refinements would be incorporated, based on feedback, such as support for more carriers such as Boolean and MemoryAddress in memory access var handles, and a new API to copy Java arrays to and from memory segments.
- The vector API would be incubated for a third time in JDK 18, having previously been incubated in JDK 16 and JDK 17. This proposal would express vector computations that compile at run time to optimal vector instructions on supported CPU architectures, achieving performance superior to equivalent scalar computations. Vector operations express a degree of parallelization enabling more work to be done on a single CPU cycle, thus producing significant performance improvements. The platform-agnostic vector API aims to provide a way to write complex algorithms in Java, using the existing HotSpot auto-vectorizer but with a user model that makes vectorization more predictable. JDK 18 would also add support for the ARM Scalar Vector Extension platform and improve performance of vector operations that accept masks on architectures that support masking in hardware.
- A preview of record patterns and array patterns, in which the Java language would be enhanced with record patterns, to deconstruct record values, and array pattens, to deconstruct array values. Record patterns, array patterns, and type patterns, which were featured in JDK 16, can be nested so as to significantly enhance the expressiveness and utility of pattern matching. Goals of the proposal include extending pattern matching to express more sophisticated, composable data queries, and not changing the syntax or semantics of type patterns.
- Specifying UTF-8 as the default charset of the standard Java APIs. UTF-8 is a variable-wide character encoding for electronic communication and is considered the web’s standard charset. Charset is character encoding capable of encoding all characters on the web. Through this change, APIs that depend on the default charset will behave consistently across all implementations, operating systems, locales, and configurations. The proposal is not intended to define new Java-standard or JDK-specific APIs. Proponents of the proposal expect that applications in many environments will see no impact from Java’s choice of UTF-8, as MacOS, many Linux distributions, and many server applications already support UTF-8. However, there is risk in other environments, the most obvious being that applications depending on the default charset will behave incorrectly when processing data produced when the default charset was unspecified. Data corruption may silently occur. The main impact is expected to be fall on users of Windows systems in Asian locales and possibly some server environments in Asian and other locales.
- Code snippets in Java API documentation, involving the introduction of an
@snippettag for JavaDoc’s Standard Doclet, to simplify inclusion of example source code in API documentation. Among goals of the plan is facilitating the validation of source code fragments by providing API access to those fragments. While correctness is the responsibility of the author, enhanced support in JavaDoc and related tools can make it easier to achieve. Other goals include enabling modern styling, such as syntax highlighting, as well as the automatic linkage of names to declarations, and enabling better IDE support for creating and editing snippets. The proposal notes that authors of API documentation often include fragments of source code in documentation comments.
Another feature that could target JDK 18 is pattern matching for switch expressions and statements, which is being previewed in the JDK 17 release.