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Java 9 Release Notes

What's new in JDK 9

Key Changes in JDK 9

  • Java Platform Module System: Introduces a new kind of Java programing component, the module, which is a named, self-describing collection of code and data. This module system:

    • Introduces a new optional phase: link time, see the jlink tool documentation and these examples.

    • Adds options to the tools javac, jlink, and java where you can specify module paths, which locate definitions of modules.

    • Introduces the modular JAR file, which is a JAR file with a module-info.class file in its root directory.

    • Introduces the JMOD format, which is a packaging format similar to JAR except it can include native code and configuration files; see the jmod tool.

    • The JDK itself has been divided into a set of modules. This change:

      • Enables you to combine the JDK's modules into a variety of configurations.
      • Restructures the JDK and JRE runtime images to accommodate modules and improve performance, security, and maintainability.
      • Defines a new URI scheme for naming modules, classes, and resources stored in a runtime image without revealing the internal structure or format of the image: jrt. A jrt URL is a hierarchical URI, per RFC 3986, with the syntax jrt:/[$MODULE[/$PATH]]. More info at JEP 220: Modular Run-Time Images
      • Removes the endorsed-standards override mechanism and the extension mechanism.
        • Before Java 9, the extension mechanism let us add classes to the JDK without having to place them on the class path. It loaded them from directories named by the system property java.ext.dirs, from lib/ext in the JRE, or from a platform-specific system-wide directory. Likewise the endorsed standards override mechanism let us replace certain APIs with custom implementations. It loaded them from the directories named by the system property java.endorsed.dirs or the lib/endorsed directory in the JRE. Aftet Java 9 removed these features, alternatives are as follows:
          • The java and javac option --patch-module injects content into modules.
          • The java and javac option --upgrade-module-path replaces an upgradeable platform module with another one.
          • The extending artifacts can be placed on the class path.
      • Removes rt.jar and tools.jar from the Java runtime image.
      • Makes most of the JDK's internal APIs inaccessible by default but leaves a few critical, widely used internal APIs accessible until supported replacements exist for all or most of their functionality.
        • To determine if some code uses internal JDK APIs, run the command jdeps -jdkinternals.

    • More info at Java Platform Module System (JSR 376)

  • JEP 223: New Version-String Scheme: Provides a simplified version-string format that helps to clearly distinguish major, minor, security, and patch update releases. The new version-string format is $MAJOR.$MINOR.$SECURITY.$PATCH.

What’s New for the Java Language in JDK 9

  • JEP 213: Milling Project Coin (more at Java Language Changes for Java SE 9)
    • Allow @SafeVargs on private instance methods.
    • Allow effectively final variables to be used as resources in the try-with-resources statement.
    • Allow the diamond with anonymous classes if the argument type of the inferred type is denotable.
    • Complete the removal, begun in Java SE 8, of the underscore from the set of legal identifier names.
    • Add support for private interface methods.

What’s New for Core Libraries in JDK 9

  • JEP 102: Process API Updates
    • Improves the API for controlling and managing operating system processes.
    • The ProcessHandle class provides the process's native process ID, arguments, command, start time, accumulated CPU time, user, parent process, and descendants. The class can also monitor processes' liveness and destroy processes. With the ProcessHandle.onExit method, the asynchronous mechanisms of the CompletableFuture class can perform an action when the process exits.
    • More info at Process API in Java Platform, Standard Edition Java Core Libraries Developer's Guide, java.lang.Process, and java.lang.ProcessHandle.
  • JEP 193: Variable Handles
    • Defines a standard means to invoke the equivalents of java.util.concurrent.atomic and sun.misc.Unsafe operations upon object fields and array elements.
    • Defines a standard set of fence operations, which consist of VarHandle static methods that enable fine-grained control of memory ordering. This is an alternative to sun.misc.Unsafe, which provides a nonstandard set of fence operations.
    • Defines a standard reachability fence operation to ensure that a referenced object remains strongly reachable.
  • JEP 254: Compact Strings
    • Adopts a more space-efficient internal representation for strings. Previously, the String class stored characters in a char array, using two bytes (16 bits) for each character. The new internal representation of the String class is a byte array plus an encoding-flag field.
    • This is purely an implementation change, with no changes to existing public interfaces.
  • JEP 264: Platform Logging API and Service
    • Defines a minimal logging API that platform classes can use to log messages, together with a service interface for consumers of those messages. A library or application can provide an implementation of this service to route platform log messages to the logging framework of its choice. If no implementation is provided, then a default implementation based on the java.util.logging API is used.
  • JEP 266: More Concurrency Updates
    • Adds further concurrency updates to those introduced in JDK 8, including an interoperable publish-subscribe framework and enhancements to the CompletableFuture API.
  • JEP 268: XML Catalogs
    • Adds a standard XML Catalog API that supports the Organization for the Advancement of Structured Information Standards (OASIS) XML Catalogs version 1.1 standard. The API defines catalog and catalog-resolver abstractions that can be used as an intrinsic or external resolver with the JAXP processors that accept resolvers.
  • JEP 269: Convenience Factory Methods for Collections
  • JEP 274: Enhanced Method Handles
    • Enhances the MethodHandle, MethodHandles, and MethodHandles.Lookup classes of the java.lang.invoke package to ease common use cases and enable better compiler optimizations. Additions include:
      • In the MethodHandles class in the java.lang.invoke package, provide new MethodHandle combinators for loops and try/finally blocks.
      • Enhance the MethodHandle and MethodHandles classes with new MethodHandle combinators for argument handling.
      • Implement new lookups for interface methods and, optionally, super constructors in the MethodHandles.Lookup class.
  • JEP 277: Enhanced Deprecation
    • Revamps the @Deprecated annotation to provide better information about the status and intended disposition of an API in the specification. Two new elements have been added:
      • @Deprecated(forRemoval=true) indicates that the API will be removed in a future release of the Java SE platform.
      • @Deprecated(since="version") contains the Java SE version string that indicates when the API element was deprecated, for those deprecated in Java SE 9 and beyond.
    • jdeprscan can be used to scan a class library (JAR file) for uses of deprecated JDK API elements.
    • More info at Enhanced Deprecation in Java Platform, Standard Edition Java Core Libraries Developer's Guide.
  • JEP 285: Spin-Wait Hints
    • Defines an API that enables Java code to hint that a spin loop is executing. A spin loop repeatedly checks to see if a condition is true, such as when a lock can be acquired, after which some computation can be safely performed followed by the release of the lock. This API is purely a hint, and carries no semantic behavior requirements. See the method Thread.onSpinWait.
  • JEP 290: Filter Incoming Serialization Data
    • Allows incoming streams of object-serialization data to be filtered to improve both security and robustness. Object-serialization clients can validate their input more easily, and exported Remote Method Invocation (RMI) objects can validate invocation arguments more easily as well.
    • Serialization clients implement a filter interface that is set on an ObjectInputStream. For RMI, the object is exported through a RemoteServerRef that sets the filter on the MarshalInputStream to validate the invocation arguments as they are unmarshalled.
  • JEP 259: Stack-Walking API
    • Provides a stack-walking API that allows easy filtering and lazy access to the information in stack traces.
    • The API supports both short walks that stop at a frame that matches given criteria, and long walks that traverse the entire stack. Stopping at a frame that matches a given criteria avoids the cost of examining all the frames if the caller is interested only in the top frames on the stack. The API enables access to Class objects when the stack walker is configured to do so.
    • More info at java.lang.Stackwalker.
  • JEP 255: Merge Selected Xerces 2.11.0 Updates into JAXP
    • Updates the JDK to support the 2.11.0 version of the Xerces parser. There is no change to the public JAXP API.
    • The changes are in the following categories of Xerces 2.11.0: Datatypes, DOM L3 Serializer, XPointer, Catalog Resolver, and XML Schema Validation (including bug fixes, but not the XML Schema 1.1 development code).

What’s New for Javadoc in JDK 9

  • JEP 221: Simplified Doclet API
    • Replaces the old Doclet API with a new simplified API that leverages other standard, existing APIs. The standard doclet has been rewritten to use the new Doclet API.
  • JEP 224: HTML5 Javadoc
    • Supports generating HTML5 output. To get fully compliant HTML5 output, any HTML content provided in documentation comments must be compliant with HTML5.
  • JEP 225: Javadoc Search
    • Provides a search box to the generated API documentation. This search box can be used to find program elements, tagged words, and phrases within the documentation.
  • JEP 261: Module System
    • Supports documentation comments in module declarations. Includes new command-line options to configure the set of modules to be documented and generates a new summary page for any modules being documented.

What’s New for Internationalization in JDK 9

  • JEP 267: Unicode 8.0
    • Supports Unicode 8.0. JDK 8 supported Unicode 6.2.
    • The Unicode 6.3, 7.0 and 8.0 standards combined introduced 10,555 characters, 29 scripts, and 42 blocks, all of which are supported in JDK 9.
  • JEP 252: CLDR Locale Data Enabled by Default
    • Uses the Common Locale Data Repository's (CLDR) XML-based locale data, first added in JDK 8, as the default locale data in JDK 9. In previous releases, the default was JRE.
    • To enable behavior compatible with JDK 8, set the system property java.locale.providers to a value with COMPAT ahead of CLDR.
    • More info at CLDR Locale Data Enabled by Default in Java Platform, Standard Edition Internationalization Guide.
  • JEP 226: UTF-8 Properties Files
    • Loads properties files in UTF-8 encoding. In previous releases, ISO-8859-1 encoding was used when loading property resource bundles. UTF-8 is a much more convenient way to represent non-Latin characters.
    • Most existing properties files should not be affected.

What’s New for the JDK 9 Installer

  • Installer Enhancements for Microsoft Windows
    • Enable or Disable Web Deployment with Installer's UI.
  • Installer Enhancements for macOS
    • Provides notification on next CPU availability after uninstalling the current CPU version.
    • Enhanced user experience while updating the JRE.

What’s New for Tools in JDK 9

  • JEP 222: jshell: The Java Shell (Read-Eval-Print Loop): Adds Read-Eval-Print Loop (REPL) functionality to the Java platform.

  • JEP 228: Add More Diagnostic Commands: Defines additional diagnostic commands to improve the ability to diagnose issues with Hotspot and the JDK. More info at jcmd and Diagnostic Tools.

  • JEP 231: Remove Launch-Time JRE Version Selection: Removes the ability to request a version of the JRE that is not the JRE being launched at launch time.

  • JEP 238: Multi-Release JAR Files: Extends the JAR file format to enable multiple, Java release-specific versions of class files to coexist in a single archive. A multirelease JAR (MRJAR) contains additional, versioned directories for classes and resources specific to particular Java platform releases. Specify versioned directories with the jar tool's --release option.

  • JEP 240: Remove the JVM TI hprof Agent: Removes the hprof agent from the JDK. The hprof agent was written as demonstration code for the JVM Tool Interface and not intended to be a production tool.

  • JEP 241: Remove the jhat Tool: Removes the jhat tool from the JDK. The jhat tool was an experimental and unsupported tool added in JDK 6. It is out of date; superior heap visualizers and analyzers have been available for many years.

  • JEP 245: Validate JVM Command-Line Flag Arguments: Validates arguments to all numerical JVM command-line flags to avoid failures and instead displays an appropriate error message if they are found to be invalid.

  • JEP 247: Compile for Older Platform Versions: Enhances javac so that it can compile Java programs to run on selected earlier versions of the platform. When using the -source or -target options, the compiled program might accidentally use APIs that are not supported on the given target platform. The --release option will prevent accidental use of APIs. --release N is roughly equivalent to:

    • for N < 9: -source N -target N -bootclasspath <documented-APIs-from-N>,
    • for N >= 9: -source N -target N --system <documented-APIs-from-N>.

  • JEP 282: jlink: The Java Linker: Assembles and optimizes a set of modules and their dependencies into a custom runtime image as defined in JEP 220.

What’s New for Security in JDK 9

  • JEP 219: Datagram Transport Layer Security (DTLS): Enables Java Secure Socket Extension (JSSE) API and the SunJSSE security provider to support DTLS Version 1.0 and DTLS Version 1.2 protocols.
  • JEP 244: TLS Application-Layer Protocol Negotiation Extension: Enables the client and server in a Transport Layer Security (TLS) connection to negotiate the application protocol to be used. With Application-Layer Protocol Negotiation (ALPN), the client sends the list of supported application protocols as part of the TLS ClientHello message. The server chooses a protocol and returns the selected protocol as part of the TLS ServerHello message. The application protocol negotiation can be accomplished within the TLS handshake, without adding network round-trips.
  • JEP 249: OCSP Stapling for TLS
    • Enables the server in a TLS connection to check for a revoked X.509 certificate revocation. The server does this during TLS handshaking by contacting an Online Certificate Status Protocol (OCSP) responder for the certificate in question. It then attaches or "staples" the revocation information to the certificate that it returns to the client so that the client can take appropriate action.
    • Enables the client to request OCSP stapling from a TLS server. The client checks stapled responses from servers that support the feature.
  • JEP 246: Leverage CPU Instructions for GHASH and RSA
    • Improves performance ranging from 34x to 150x for AES/GCM/NoPadding using GHASH HotSpot intrinsics. GHASH intrinsics are accelerated by the PCLMULQDQ instruction on Intel x64 CPU and the xmul/xmulhi instructions on SPARC.
    • Improves performance up to 50% for BigInteger squareToLen and BigInteger mulAdd methods using RSA HotSpot intrinsics.
    • RSA intrinsics apply to the java.math.BigInteger class on Intel x64.
    • A new security property jdk.security.provider.preferred is introduced to configure providers that offer significant performance gains for specific algorithms.
  • JEP 273: DRBG-Based SecureRandom Implementations
    • Provides the functionality of Deterministic Random Bit Generator (DRBG) mechanisms as specified in NIST SP 800-90Ar1 in the SecureRandom API.
    • The DRBG mechanisms use modern algorithms as strong as SHA-512 and AES-256.
    • Each of these mechanisms can be configured with different security strengths and features to match user requirements.
  • JEP 288: Disable SHA-1 Certificates
    • Improves the security configuration of the JDK by providing a more flexible mechanism to disable X.509 certificate chains with SHA-1-based signatures
    • Disables SHA-1 in TLS Server certificate chains anchored by roots included by default in the JDK; local or enterprise certificate authorities (CAs) are not affected.
  • JEP 229: Create PKCS12 Keystores by Default
    • Modifies the default keystore type from JKS to PKCS12. PKCS#12 is an extensible, standard, and widely supported format for storing cryptographic keys. PKCS12 keystores improve confidentiality by storing private keys, trusted public key certificates, and secret keys. This feature also opens opportunities for interoperability with other systems such as Mozilla, Microsoft's Internet Explorer, and OpenSSL that support PKCS12.
    • The SunJSSE provider supplies a complete implementation of the PKCS12 java.security.KeyStore format for reading and writing PKCS12 files.
  • JEP 287: SHA-3 Hash Algorithms
    • Supports SHA-3 cryptographic hash functions as specified in NIST FIPS 202.
    • The following additional standard algorithms are supported by the java.security.MessageDigest API: SHA3-224, SHA3-256, SHA3-384, and SHA3-512.
    • The following providers support SHA-3 algorithm enhancements:
      • SUN provider: SHA3-224, SHA3-256, SHA3-384, and SHA3-512
      • OracleUcrypto provider: SHA-3 digests supported by Solaris 12.0

What’s New for Deployment in JDK 9

  • Deprecate the Java Plug-in
    • Deprecates the Java Plug-in and associated applet technologies in Oracle's JDK 9 builds. While still available in JDK 9, these technologies will be considered for removal from the Oracle JDK and JRE in a future release.
    • Applets and JavaFX applications embedded in a web page require the Java Plug-in to run. It should be considered to rewrite these types of applications as Java Web Start or self-contained applications.
  • Enhanced Java Control Panel
    • Improves the grouping and presentation of options within the Java Control Panel. Information is easier to locate, a search field is available, and modal dialog boxes are no longer used.
    • The location of some options has changed from previous versions of the Java Control Panel.
  • JEP 275: Modular Java Application Packaging
    • Integrates features from Project Jigsaw into the Java Packager, including module awareness and custom runtime creation.
    • Leverages the jlink tool to create smaller packages.
    • Creates applications that use the JDK 9 runtime only. Cannot be used to package applications with an earlier release of the JRE.
  • JEP 289: Deprecate the Applet API: Deprecates the Applet API, which is becoming less useful as web browser vendors remove support for Java browser plug-ins. While still available in JDK 9, the Applet class will be considered for removal in a future release. Consider rewriting applets as Java Web Start or self-contained applications.

What’s New for the JVM in JDK 9

  • JEP 165: Compiler Control
    • Provides a way to control JVM compilation through compiler directive options. The level of control is runtime-manageable and method-specific. Compiler Control supersedes, and is backward compatible, with CompileCommand.
  • JEP 197: Segmented Code Cache
    • Divides the code cache into distinct segments, each of which contains compiled code of a particular type, to improve performance and enable future extensions.
  • JEP 276: Dynamic Linking of Language-Defined Object Models
    • Dynamically links high-level object operations at run time, such as read a property, write a property, and invoke a function, to the appropriate target method handles. It links these operations to target method handles based on the actual types of the values passed. These object operations are expressed as invokedynamic sites.
    • While java.lang.invoke provides a low-level API for dynamic linking of invokedynamic call sites, it doesn't provide a way to express higher level operations on objects nor methods that implement them.

What’s New for JVM Tuning in JDK 9

  • Improve G1 Usability, Determinism, and Performance
    • Enhances the Garbage-First (G1) garbage collector to automatically determine several important memory-reclamation settings. Previously these settings had to be set manually to obtain optimal results. In addition, fixes issues with the usability, determinism, and performance of the G1 garbage collector.
  • JEP 158: Unified JVM Logging (more info at the -Xloggc java option) and Enable Logging with the JVM Unified Logging Framework
  • JEP 214: Remove GC Combinations Deprecated in JDK 8
    • This means that the following GC combinations no longer exist:
      • DefNew + CMS
      • ParNew + SerialOld
      • Incremental CMS
    • The "foreground" mode for Concurrent Mark Sweep (CMS) has also been removed. The following command-line flags have been removed:
      • -Xincgc
      • -XX:+CMSIncrementalMode
      • -XX:+UseCMSCompactAtFullCollection
      • -XX:+CMSFullGCsBeforeCompaction
      • -XX:+UseCMSCollectionPassing
    • The command line flag -XX:+UseParNewGC no longer has an effect. ParNew can only be used with CMS and CMS requires ParNew. Thus, the -XX:+UseParNewGC flag has been deprecated and will likely be removed in a future release.
  • JEP 248: Make G1 the Default Garbage Collector
    • Makes Garbage-First (G1) the default garbage collector (GC) on 32- and 64-bit server configurations. Using a low-pause collector such as G1 provides a better overall experience, for most users, than a throughput-oriented collector such as the Parallel GC, which was previously the default.
  • JEP 271: Unified GC Logging
    • Reimplements Garbage Collection (GC) logging using the unified JVM logging framework introduced in JEP 158. GC logging is re-implemented in a manner consistent with the current GC logging format; however, some differences exist between the new and old formats. More info at Enable Logging with the JVM Unified Logging Framework in Java Platform], Standard Edition Tools Reference.
  • JEP 291: Deprecate the Concurrent Mark Sweep (CMS) Garbage Collector
    • Deprecates the Concurrent Mark Sweep (CMS) garbage collector. A warning message is issued when it is requested on the command line, using the -XX:+UseConcMarkSweepGC option. The Garbage-First (G1) garbage collector is intended to be a replacement for most uses of CMS.

What's New for Nashorn in JDK 9

What’s New for Client Technologies in JDK 9

  • JEP 251: Multi-Resolution Images
    • Enables a set of images with different resolutions to be encapsulated into a single multiresolution image. This could be useful for applications to adapt to display devices whose resolutions may vary from approximately 96dpi to 300dpi during run time.
    • The interface java.awt.image.MultiResolutionImage encapsulates a set of images with different resolutions into a single multiresolution image, which enables applications to easily manipulate and display images with resolution variants.
  • JEP 253: Prepare JavaFX UI Controls and CSS APIs for Modularization
    • Provides public APIs for JavaFX UI controls and CSS functionality that were previously available only through internal packages but are now inaccessible due to modularization.
    • The new package javafx.scene.control.skin consists of a set of classes that provides a default implementation for the skin (or the look) of each UI control.
    • The new class CssParser is a CSS parser that returns a Stylesheet object, which gives you more control over the CSS styling of your application. It’s part of the CSS API (the javafx.css package). The CSS API includes new support classes, including a set of standard converters used by the parser; more info at javafx.css.converter package.
  • JEP 256: BeanInfo Annotations
    • Replaces the @beaninfo Javadoc tag with the annotation types JavaBean, BeanProperty, and SwingContainer.
    • These annotation types set the corresponding feature attributes during BeanInfo generation at runtime. Thus, you can more easily specify these attributes directly in Bean classes instead of creating a separate BeanInfo class for every Bean class. It also enables the removal of automatically generated classes, which makes it easier to modularize the client library.
  • JEP 262: TIFF Image I/O
    • Adds Tag Image File Format (TIFF) reading and writing as standard to the package javax.imageio. The new package javax.imageio.plugins.tiff provides classes that simplify the optional manipulation of TIFF metadata.
  • JEP 263: HiDPI Graphics on Windows and Linux
    • Automatically scales and sizes AWT and Swing components for High Dots Per Inch (HiDPI) displays on Windows and Linux.
    • The JDK already supports HiDPI "retina displays" on OS X.
    • Prior to this release, on Windows and Linux, Java applications were sized and rendered based on pixels, even on HiDPI displays that can have pixel densities two to three times as high as traditional displays. This led to GUI components and windows that were too small to read or use.
  • JEP 272: Platform-Specific Desktop Features
    • Adds additional methods to the class java.awt.Desktop that enable you to interact with the desktop, including the following:
      • Show custom About and Preferences windows.
      • Handle requests to open or print a list of files.
      • Handle requests to open a URL.
      • Open the native help viewer application.
      • Set the default menu bar.
      • Enable or disable the application to be suddenly terminated.
    • These new methods replace the functionality of the internal APIs contained in the OS X package com.apple.eawt, which are not accessible by default in JDK 9. Note that the package com.apple.eio is no longer accessible.
  • JEP 283: Enable GTK 3 on Linux
    • Enables Java graphical applications, whether based on JavaFX, Swing, or Abstract Window Toolkit (AWT), to use either the GTK+ version 2 or version 3 on Linux or Solaris.
    • By default, the JDK on Linux or Solaris uses GTK+ 2 if available; if not, it uses GTK+ 3.
    • To use a specific version of GTK+, the system property jdk.gtk.version can be set. This system property may have a value of 2, 2.2, or 3. This property must be set before your application loads GTK+, and it must not conflict with a GTK+ version that may have been loaded earlier by another toolkit.

Important Changes and Information

Enhancements and Notes

Removed APIs, Features, and Options

Deprecated APIs, Features, and Options

Other Notes

Java Mission Control 6.0 Release Notes