JDK 16: The new features in Java 16

Oracle’s Java Growth Package (JDK) 16 is now out there as a manufacturing launch, as of March 16. The brand new options in JDK 16 vary from a second preview of sealed lessons to data to concurrent thread-stack processing for rubbish assortment.

JDK 16 is the reference implementation of Java 16, the model of normal Java that follows JDK 15, which arrived September 15. JDK 16 is a characteristic launch backed by simply six months of help from Oracle. JDK 17, due in September, can be a long-term help (LTS) launch. Oracle frames JDK 16 as a place to begin for migration to JDK 17, with customers capable of check on JDK 16 previous to deploying to JDK 17. LTS releases are revealed each three years.

Seventeen proposals formally goal JDK 16. The brand new capabilities embody:

  • The warnings for value-based classes proposal designates the primitive wrapper lessons as value-based and deprecates their constructors for removing, prompting new deprecation warnings. Warnings are offered about improper makes an attempt to synchronize on cases of any value-based lessons within the Java platform. Driving this effort is the Valhalla Project, which is pursuing a big enhancement to the Java programming mannequin within the type of primitive lessons. Primitive lessons declare cases to be identity-free and able to inline or flattened representations, the place cases may be copied freely between reminiscence areas and encoded utilizing values of cases’ fields. The design and implementation of primitive lessons in Java is now sufficiently mature that the migration of sure lessons of the Java platform to primitive lessons may be anticipated in a future launch. Candidates for migration are informally designated as value-based classes in API specs.
  • Previewed in JDK 15 and once more in JDK 16, sealed classes and interfaces limit which different lessons and interfaces might lengthen or implement them. Objectives of the plan embody permitting the creator of a category or interface to regulate the code chargeable for implementing it, present a extra declarative means than entry modifiers to limit the usage of a superclass, and help future instructions in sample matching by offering a basis for evaluation of patterns.
  • Strong encapsulation of JDK internals by default, apart from important inside APIs reminiscent of misc.Unsafe. Customers can select the relaxed robust encapsulation that has been the default since JDK 9. Objectives of this proposal embody bettering the safety and maintainability of the JDK, as a part of Project Jigsaw, and inspiring builders emigrate from utilizing inside parts to utilizing customary APIs in order that each builders and finish customers can replace simply to future Java releases. This proposal does carry a main danger that current Java code will fail to run. Builders are inspired to make use of the jdeps instrument to establish code that is dependent upon inside parts of the JDK and swap to standard replacements when out there. Builders can use an current launch, reminiscent of JDK 11, to check current code by utilizing --illegal-access=warn to establish inside parts accessed through reflection, utilizing --illegal-access=debug to pinpoint errant code, and testing with --illegal-access=deny.
  • Foreign linker API, providing statically typed, pure-Java entry to native code. This API can be in an incubator stage in JDK 16. Along with the proposed foreign-memory entry API, the international linker API will significantly simplify the in any other case error-prone strategy of binding to a local library. This plan is meant to switch JNI (Java Native Interface) with a superior pure-Java improvement mannequin, to supply C help, and, over time, to be versatile sufficient to accommodate help for different platforms, reminiscent of 32-bit x86, and international features written in languages aside from C, reminiscent of C++. Efficiency needs to be higher than or corresponding to JNI.
  • Moving ZGC (Z Garbage Collector) thread-stack processing from safepoints to a concurrent part. Objectives of this plan embody eradicating thread-stack processing from ZGC safepoints; making stack processing lazy, cooperative, concurrent, and incremental; eradicating all different per-thread root processing from ZGC safepoints; and offering a mechanism for different HotSpot VM subsystems to lazily course of stacks. ZGC is meant to make GC pauses and scalability points in HotSpot a factor of the previous. Up to now, GC operations that scale with the scale of the heap and the scale of metaspace have been moved out of safepoint operations and into concurrent phases. These have included marking, relocation, reference processing, class unloading, and most root processing. The one actions nonetheless achieved in GC safepoints are a subset of root processing and a time-bounded marking termination operation. These roots have included Java thread stacks and different thread roots, with these roots being problematic as a result of they scale with the variety of threads. To maneuver past the present state of affairs, per-thread processing, together with stack scanning, should be moved to a concurrent part. With this plan, the throughput value of the improved latency needs to be insignificant and the time spent inside ZGC safepoints on typical machines needs to be lower than one millisecond.
  • An elastic metaspace capability, which returns unused HotSpot VM class metadata (metaspace) reminiscence extra promptly to the OS, reduces metaspace footprint and simplifies metaspace code to scale back upkeep prices. Metaspace has had points with excessive off-heap reminiscence use. The plan requires changing the prevailing reminiscence allocator with a buddy-based allocation scheme, offering an algorithm to divide reminiscence into partitions to fulfill reminiscence requests. This strategy has been utilized in locations such because the Linux kernel and can make it sensible to allocate reminiscence in smaller chunks to scale back class-loader overhead. Fragmentation additionally can be diminished. As well as, the dedication of reminiscence from the OS to reminiscence administration arenas can be achieved lazily, on demand, to scale back the footprint for loaders that begin out with giant arenas however don’t use them instantly or may not use them to their full extent. To totally exploit the elasticity provided by buddy allocation, metaspace reminiscence can be organized into uniformly sized granules that may be dedicated and uncommitted independently of one another.
  • Enablement of C++ 14 language features, to permit the usage of C++ 14 capabilities in JDK C++ supply code and provides particular steering about which of those options could also be utilized in HotSpot VM code. By JDK 15, language options utilized by C++ code within the JDK have been restricted to the C++98/03 language requirements. With JDK 11, the supply code was up to date to help constructing with newer variations of the C++ customary. This consists of having the ability to construct with latest variations of compilers that help C++ 11/14 language options. This proposal doesn’t suggest any fashion or utilization modifications for C++ code that’s used outdoors of HotSpot. However to benefit from C++ language options, some build-time modifications are required, relying on the platform compiler.
  • A vector API in an incubator stage, during which the JDK can be fitted with an incubator module, jdk.incubator.vector, to specific vector computations that compile to optimum vector hardware directions on supported CPU architectures, to attain superior efficiency to equal scalar computations. The vector API gives a mechanism to jot down complicated vector algorithms in Java, utilizing pre-existing help within the HotSpot VM for vectorization however with a consumer mannequin that makes vectorization extra predictable and strong. Objectives of the proposal embody offering a transparent and concise API to specific a spread of vector computations, being platform-agnostic by supporting a number of CPU architectures, and providing dependable runtime compilation and efficiency on x64 and AArch64 architectures. Swish degradation is also a aim, during which a vector computation would degrade gracefully and nonetheless perform if it can’t be totally expressed at runtime as a sequence of hardware vector directions, both as a result of an structure doesn’t help some directions or one other CPU structure is just not supported.
  • Porting the JDK to the Windows/AArch64 platform. With the discharge of recent server-class and shopper AArch64 (ARM64) hardware, Home windows/AArch64 has turn into an essential platform resulting from demand. Whereas the porting itself is already principally full, the main focus of this proposal includes integration of the port into the mainline JDK repository.
  • Porting of the JDK to Alpine Linux and to different Linux distributions that use musl as their main C library, on x64 and AArch64 architectures. Musl is a Linux implementation of the usual library performance described within the ISO C and Posix requirements. Alpine Linux is extensively adopted in cloud deployments, microservices, and container environments resulting from its small picture measurement. A Docker picture for Linux is smaller than 6MB. Letting Java run out-of-the-box in such settings will permit Tomcat, Jetty, Spring, and different fashionable frameworks to work in these environments natively. By utilizing jlink to scale back the scale of the Java runtime, a consumer can create a good smaller picture tailor-made to run a selected software.
  • Providing records classes that act as clear carriers for immutable information. Information may be thought of nominal tuples. One of the extensively anticipated options within the launch, decreasing the ceremony of Java by reducing boilerplate code, data was previewed in JDK 14 and JDK 15. Objectives of the plan embody devising an object-oriented assemble that expresses a easy aggregation of values, serving to builders give attention to modeling immutable information quite than extensible habits, routinely implementing data-driven strategies reminiscent of equals and accessors, and preserving longstanding Java ideas reminiscent of nominal typing and migration compatibility.
  • The addition of Unix-domain socket channels, during which Unix-domain (AF_UNIX) socket help is added to the socket channel and server socket channel APIs within the nio.channels bundle. The plan additionally extends the inherited channel mechanism to help Unix-domain socket channels and server socket channels. Unix-domain sockets are used for inter-process communications on the identical host. They’re just like TCP/IP sockets in most respects besides that they’re addressed by filesystem path names quite than IP addresses and port numbers. The aim of the brand new functionality is to help all options of Unix-domain socket channels which might be widespread throughout main Unix platforms and Home windows. Unix-domain socket channels will behave the identical as current TCP/IP channels when it comes to learn/write habits, connection setup, acceptance of incoming connections by servers, and multiplexing with different non-blocking selectable channels in a selector. Unix-domain sockets are safer and extra environment friendly than TCP/IP loopback connections for native, inter-process communications.
  • A foreign-memory access API, permitting Java applications to securely entry international reminiscence outdoors the Java heap. Beforehand incubated in each JDK 14 and JDK 15, the foreign-memory entry API can be re-incubated in JDK 16, including refinements. Adjustments have been made together with a clearer separation of roles between the MemorySegment and MemoryAddresses interfaces. Objectives of this proposal embody offering a single API to function on varied sorts of international reminiscence, together with native, persistent, and managed heap reminiscence. The API mustn’t undermine the security of the JVM. Motivating the proposal is that many Java applications entry international reminiscence, reminiscent of Ignite, Memcached, and MapDB. However the Java API doesn’t present a passable resolution for accessing international reminiscence.
  • Pattern matching for the instanceof operator, which additionally was previewed in each JDK 14 and JDK 15. It could be finalized in JDK 16. Sample matching permits widespread logic in a program, particularly the conditional extraction of parts from objects, to be expressed extra concisely and safely.
  • Providing the jpackage tool for packaging self-contained Java applications. Launched as an incubating instrument in JDK 14, jpackage remained in incubation in JDK 15. With JDK 16, jpackage strikes to manufacturing, supporting native bundle codecs to provide customers a pure set up expertise and permit launch-time parameters to be specified at packaging time. Codecs embody msi and exe on Home windows, pkg and dmg on MacOS, and deb and rpm on Linux. The instrument may be invoked straight from the command line or programmatically. The brand new packaging instrument addresses a state of affairs during which many Java purposes must be put in on native platforms in a first-class means, quite than being positioned on the category path or module path. An installable bundle appropriate for the native platform is required.
  • Migration of OpenJDK source code repositories from Mercurial to Git. Driving this effort are benefits in model management system metadata measurement and out there instruments and internet hosting.
  • Migration to GitHub, associated to the Mercurial-to-Git migration, with JDK 16 supply code repositories to be on the favored code-sharing website. JDK characteristic releases and JDK replace releases for Java 11 and later can be a part of this plan. The transition to Git, GitHub, and Skara for the Mercurial JDK and JDK-sandbox was achieved on September 5 and is open for contributions.  

Downloads of Oracle JDK may be discovered at oracle.com. Open supply builds of JDK 16 for Linux, Home windows, and MacOS may be discovered at jdk.java.net. Oracle affords subscriptions to its model of normal Java, offering help for the platform. The corporate famous that many Java-based applied sciences, such because the Apache Lucene search library, Apache Tomcat servlet container, and Gradle construct instrument, already help JDK 16.

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