Key:

JDK-X  - https://bugs.openjdk.java.net/browse/JDK-X
CVE-XXXX-YYYY: https://cve.mitre.org/cgi-bin/cvename.cgi?name=XXXX-YYYY

New in release OpenJDK 21.0.0 (2023-09-XX):
===========================================
Major changes are listed below.  Some changes may have been backported
to earlier releases following their first appearance in OpenJDK 18
through to 21.

NEW FEATURES
============

Language Features
=================

Pattern Matching for switch
===========================
https://openjdk.org/jeps/406
https://openjdk.org/jeps/420

Enhance the Java programming language with pattern matching for
`switch` expressions and statements, along with extensions to the
language of patterns. Extending pattern matching to `switch` allows an
expression to be tested against a number of patterns, each with a
specific action, so that complex data-oriented queries can be
expressed concisely and safely.

This was a preview feature (http://openjdk.java.net/jeps/12) in
OpenJDK 17 (JEP 406) and sees a second preview in OpenJDK 18 (JEP
420).

Library Features
================

UTF-8 by Default
================
https://openjdk.org/jeps/400

Specify UTF-8 as the default charset of the standard Java APIs. With
this change, APIs that depend upon the default charset will behave
consistently across all implementations, operating systems, locales,
and configurations.

Reimplement Core Reflection with Method Handles
===============================================
https://openjdk.org/jeps/416

Reimplement java.lang.reflect.Method, Constructor, and Field on top of
java.lang.invoke method handles. Making method handles the underlying
mechanism for reflection will reduce the maintenance and development
cost of both the java.lang.reflect and java.lang.invoke APIs.

Vector API
==========
https://openjdk.org/jeps/338
https://openjdk.org/jeps/414
https://openjdk.org/jeps/417

Provide an initial iteration of an incubator module,
`jdk.incubator.vector`, to express vector computations that reliably
compile at runtime to optimal vector hardware instructions on
supported CPU architectures and thus achieve superior performance to
equivalent scalar computations.

This is an incubation feature (https://openjdk.java.net/jeps/11)
introduced in OpenJDK 16 (JEP 338). A second round of incubation took
place in OpenJDK 17 (JEP 414) and OpenJDK 18 (JEP 417) sees a third.

Internet-Address Resolution SPI
===============================
https://openjdk.org/jeps/418

Define a service-provider interface (SPI) for host name and address
resolution, so that java.net.InetAddress can make use of resolvers
other than the platform's built-in resolver.

Foreign Function & Memory API
=============================
https://openjdk.org/jeps/412
https://openjdk.org/jeps/419

Introduce an API by which Java programs can interoperate with code and
data outside of the Java runtime. By efficiently invoking foreign
functions (i.e., code outside the JVM), and by safely accessing
foreign memory (i.e., memory not managed by the JVM), the API enables
Java programs to call native libraries and process native data without
the brittleness and danger of JNI.

This API is an incubation feature (https://openjdk.java.net/jeps/11)
introduced in OpenJDK 17 (JEP 412), and is an evolution of the Foreign
Memory Access API (OpenJDK 14 through 16) and Foreign Linker API
(OpenJDK 16) (see release notes for java-17-openjdk). OpenJDK 18 sees
a second round of incubation (JEP 419).

Tools
=====

Simple Web Server
=================
https://openjdk.org/jeps/408

Provide a command-line tool, `jwebserver`, to start a minimal web
server that serves static files only. No CGI or servlet-like
functionality is available. This tool will be useful for prototyping,
ad-hoc coding, and testing purposes, particularly in educational
contexts.

Code Snippets in Java API Documentation
=======================================
https://openjdk.org/jeps/413

Introduce an @snippet tag for JavaDoc's Standard Doclet, to simplify
the inclusion of example source code in API documentation.

DEPRECATIONS
============

Deprecate Finalization for Removal
==================================
https://openjdk.org/jeps/421

Deprecate finalization for removal in a future release. Finalization
remains enabled by default for now, but can be disabled to facilitate
early testing. In a future release it will be disabled by default, and
in a later release it will be removed. Maintainers of libraries and
applications that rely upon finalization should consider migrating to
other resource management techniques such as the try-with-resources
statement and cleaners.
