The JDK is the Java Development Kit, the full-featured SDK for Java. It has everything the JRE has, but also the compiler (javac) and tools (like javadoc and jdb). It is capable of creating and compiling programs.
The new Oracle Technology Network License Agreement for Oracle Java SE is substantially different from prior Oracle JDK licenses. The new license permits certain uses, such as personal use and development use, at no cost — but other uses authorized under prior Oracle JDK licenses may no longer be available.
Sometimes, even if you are not planning to do any Java development on a computer, you still need the JDK installed. For example, if you are deploying a web application with JSP, you are technically just running Java programs inside the application server. Why would you need the JDK then? Because the application server will convert JSP into Java servlets and needs to use the JDK to compile the servlets.
These notes describe important changes, enhancements, removed APIs and features, deprecated APIs and features, and other information about JDK 16 and Java SE 16. In some cases, the descriptions provide links to additional detailed information about an issue or a change. This page does not duplicate the descriptions provided by the Java SE 16 ( JSR 391) Platform Specification, which provides informative background for all specification changes and might also include the identification of removed or deprecated APIs and features not described here.
This section describes some of the enhancements in Java SE 16 and JDK 16. In some cases, the descriptions provide links to additional detailed information about an issue or a change. The APIs described here are those that are provided with the Oracle JDK. It includes a complete implementation of the Java SE 16 Platform and additional Java APIs to support developing, debugging, and monitoring Java applications. Another source of information about important enhancements and new features in Java SE 16 and JDK 16 is the Java SE 16 ( JSR 391) Platform Specification, which documents the changes to the specification made between Java SE 15 and Java SE 16. This document includes descriptions of those new features and enhancements that are also changes to the specification. The descriptions also identify potential compatibility issues that you might encounter when migrating to JDK 16.
JEP 396: Strongly Encapsulate JDK Internals by Default (JDK-8256299)
Strongly encapsulate all internal elements of the JDK by default, except for critical internal APIs such as sun.misc.Unsafe. Allow end users to choose the relaxed strong encapsulation that has been the default since JDK 9.
With this change, the default value of the launcher option –illegal-access is now deny rather than permit. As a consequence, existing code that uses most internal classes, methods, or fields of the JDK will fail to run. Such code can be made to run on JDK 16 by specifying –illegal-access=permit. That option will, however, be removed in a future release.
For further details, please see JEP 396.
JEP 390: Warnings for Value-based Classes (JDK-8249100)
Users of the value-based classes provided by the standard libraries—notably including users of the primitive wrapper classes—should avoid relying on the identity of class instances. Programmers are strongly discouraged from calling the wrapper class constructors, which are now deprecated for removal. New javac warnings discourage synchronization on value-based class instances. Runtime warnings about synchronization can also be activated, using command-line option -XX:DiagnoseSyncOnValueBasedClasses.
For further details, see JEP 390.
JEP 389: Foreign Linker API (Incubator) (JDK-8249755)
Introduce an API that offers statically-typed, pure-Java access to native code. This API, together with the Foreign-Memory API (JEP 393), will considerably simplify the otherwise error-prone process of binding to a native library.
For further details, see JEP 389.
JEP 393: Foreign-Memory Access API (Third Incubator) (JDK-8253415)
Introduce an API to allow Java programs to safely and efficiently access foreign memory outside of the Java heap.
For further details, see JEP 393.
Add InvocationHandler::invokeDefault Method for Proxy’s Default Method Support (JDK-8159746)
A new method, invokeDefault, has been added to the java.lang.reflect.InvocationHandler interface to allow a default method defined in a proxy interface to be invoked.
JEP 380: Unix domain sockets (JDK-8238588)
Provides support for Unix domain sockets (AF_UNIX) in the java.nio.channels, SocketChannel, and ServerSocketChannel classes. See JEP-380 for more information.
See also the following release note for information about the limitations in the support on Windows in JDK16.
Day Period Support Added to java.time Formats (JDK-8247781)
A new formatter pattern, letter ‘B’, and its supporting method have been added to java.time.format.DateTimeFormatter/DateTimeFormatterBuilder classes. The pattern and method translate day periods defined in Unicode Consortium’s CLDR (https://unicode.org/reports/tr35/tr35-dates.html#dayPeriods). Applications can now express periods in a day, such as “in the morning” or “at night”, not just am/pm. The following example demonstrates translating the day periods:
This example produces day period text depending on the time of the day and locale.
Add Stream.toList() Method (JDK-8180352)
A new method toList has been added to the java.util.Stream interface. This introduces a potential source incompatibility with classes that implement or interfaces that extend the Stream interface and that also statically import a toList method from elsewhere, for example, Collectors.toList. References to such methods must be changed to use a qualified name instead of a static import.
Complete release notes here.