This Specification defines version 16 of the Java Platform, Standard Edition (“Java SE 16”). The Reference Implementation of this Specification is the Java Development Kit, version 16 (“JDK 16”).
|4||Component JSR Specifications|
|8||APIs proposed for removal|
|A1||Complete API Specification|
|A2||API Specification differences|
|A3||Java Language & Virtual Machine Specifications|
|A4||JAR File Specification|
|A5||Java AWT Native Interface (JAWT) Specification & Guide|
|A6||Java Debug Wire Protocol (JDWP)|
|A7||Java Native Interface (JNI) Specification|
|A8||Java Object Serialization Specification|
|A9||Java Remote Method Invocation (RMI) Specification|
|A10||Java Security Standard Algorithm Names|
|A11||JVM Tool Interface (JVM TI)|
This release continues the evolution of the Platform to ensure the
broadest possible success of the core Java technology. It standardizes
record classes and pattern matching for
instanceof in the
Java language, and previews sealed classes. It adds support for
Unix-domain sockets in the API, and prepares for future enhancements to
the Java programming model by refining the notion of value-based classes.
In addition, and in contrast to earlier releases, it requires strong
encapsulation of an Implementation’s modules by default.
This document directly specifies API features, enhancements, clarifications, and bug fixes. It also specifies features by reference to other Specifications which are revised in Maintenance Releases of existing JSRs. The specifications of these changes are contained in two accompanying documents: Annex 1 is the complete Java SE 16 API Specification and Annex 2 is an annotated API specification showing the exact differences relative to Java SE 15. Informative background for these changes may be found in the list of approved Compatibility & Specification Review (CSR) requests for this release.
This Specification includes the Java SE 16 Editions of The Java Language Specification and The Java Virtual Machine Specification in Annex 3. The Java SE 16 Editions contain all corrections and clarifications made since the Java SE 15 Editions, as well as additions for new features. Annex 3 also presents changes to The Java Language Specification and The Java Virtual Machine Specification in connection with preview features in Java SE 16.
This Specification includes the Java SE 16 versions of additional narrative specifications in Annexes 4 — 11. The Java SE 16 versions contain all corrections and clarifications made since the Java SE 15 versions, as well as additions for new features. The Java Object Serialization Specification in Annex 8 contains the most significant changes which were made in connection with Records a final, permanent feature added in Java SE 16.
Changes to the Java SE Platform Specification are categorized as either features or enhancements. A feature is, roughly speaking, a change of which at least one of the following statements is true:
Any addition that is not a feature is considered an enhancement.
There is, obviously, room for judgment when interpreting this definition. In order to maximize the visibility of Platform revisions we generally tend to consider borderline items to be features rather than enhancements.
Some Component JSR Specifications previously incorporated into the Platform are still available separately or have significant Specifications themselves. Changes to their Specifications are therefore made in separate Maintenance Releases, which are incorporated here by reference:
Each Component JSR Specification, or revision thereto, may be related to one or more features in the detailed list below.
Work on features in the Java SE 16 Reference Implementation is organized in terms of JDK Enhancement Proposals (JEPs). Each feature description gives a link to the corresponding JEP document as a convenience, but that document is not a normative part of this Specification. Some features are included in the Java SE 16 Reference Implementation on a preview basis, to gain exposure before achieving permanent status in a later release of the Java SE Platform.
Enhance the Java programming language with pattern matching for the
allows common logic in a program, namely the conditional extraction of
components from objects, to be expressed more concisely and safely.
Enhance the Java programming language with records, which are classes that act as transparent carriers for immutable data. Records can be thought of as nominal tuples.
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.
Designate the primitive wrapper classes as value-based and deprecate their constructors for removal, prompting new deprecation warnings. Provide warnings about improper attempts to synchronize on instances of any value-based classes in the Java Platform.
Preview features A preview language or VM feature is a new feature of the Java SE Platform that is fully specified, fully implemented, and yet impermanent. This Specification incorporates the Java SE 12 Platform Specification (JSR 386), subsection Preview features by reference.
A module is a named set of packages designed for reuse. A specification governed by the JCP defines standard packages, and may group them into one or more standard modules.
This Specification groups the standard packages of the Java SE Platform into 21 standard modules, which we refer to as the Java SE modules. The name of a Java SE module always starts with the string "java.". The complete list of such modules is:
Compared to Java SE 15, this Specification does not add or remove any modules.
The module graph The Java SE modules depend upon each other as stated in their specifications, which are part of the overall API Specification. The corresponding complete Java SE module graph has too many edges to be displayed easily in visual form; here is the transitive reduction of the directed acyclic graph, in which redundant edges are omitted (click to enlarge):
Here is how to read this visualization of the module graph:
If one module depends upon another, and it grants implied readability to that module via a requires transitive directive, then there is an edge from the first module to the second.
At the very bottom is the java.base module, which contains essential classes such as java.lang.Object and java.lang.String. The base module depends upon no module, and every other module depends upon the base module.
At the top is the java.se module, which gathers together all of the modules that comprise the Java SE Platform. This is an example of an aggregator module, which logically gathers the content of other modules by granting implied readability to them, but adds no content of its own. A run-time system configured to contain the java.se module will contain all of the packages of the Java SE Platform.
A module is a Java SE module — that is, considered part of the Java SE Platform Specification — if and only if it is a standard module reachable from the java.se module.
Relaxing strong encapsulation As an aid to migration, an Implementation may provide a means to invoke its run-time system with one or more packages of one or more of its modules open to code in all unnamed modules, i.e., to code on the class path. If the run-time system is invoked in this way, and if by doing so some invocations of the reflection APIs succeed where otherwise they would have failed, then the first such invocation must cause a warning to be issued on the standard error stream. Later such invocations may also cause warnings to be issued.
(The Reference Implementation provides this capability via the
An Implementation must not, by default, relax the strong encapsulation of any of its modules. That is, its run-time system must not customarily behave as if various packages in the Implementation’s modules are open when they are not open according to their module declarations. A package, or an entire module, is open to code in all unnamed modules if and only if:
A future revision of this Specification is expected to disallow relaxed strong encapsulation entirely.
This section may be compared to the corresponding section that appeared in Java SE 9 through 15.
The following API was removed from the Java SE Platform by this Platform Specification. The number in parentheses indicates the Java SE Platform Specification which first proposed its removal.
The following APIs were proposed for removal from the Java SE Platform by the Platform Specifications for Java SE 9, Java SE 10, Java SE 13, Java SE 14, and Java SE 15. They are not removed in this release of the Java SE Platform. They continue to be eligible for removal in a future release.
The following APIs are proposed for removal from the Java SE Platform
by this Platform Specification. They are annotated as
forRemoval=true, following the
convention established by
This makes them eligible for removal in a future release.