[DevoxxUS2017] 55 New Features in JDK 9: A Comprehensive Overview
At DevoxxUS2017, Simon Ritter, Deputy CTO at Azul Systems, delivered a detailed exploration of the 55 new features in JDK 9, with a particular focus on modularity through Project Jigsaw. Simon, a veteran Java evangelist, provided a whirlwind tour of the enhancements, categorizing them into features, standards, JVM internals, specialized updates, and housekeeping changes. His presentation equipped developers with the knowledge to leverage JDK 9’s advancements effectively. This post examines the key themes of Simon’s talk, highlighting how these features enhance Java’s flexibility, performance, and maintainability.
Modularity and Project Jigsaw
The cornerstone of JDK 9 is Project Jigsaw, which introduces modularity to the Java platform. Simon explained that the traditional rt.jar file, containing over 4,500 classes, has been replaced with 94 modular components in the jmods directory. This restructuring encapsulates private APIs, such as sun.misc.Unsafe, to improve security and maintainability, though it poses compatibility challenges for libraries relying on these APIs. To mitigate this, Simon highlighted options like the --add-exports and --add-opens flags, as well as a “big kill switch” (--permit-illegal-access) to disable modularity for legacy applications. The jlink tool further enhances modularity by creating custom runtimes with only the necessary modules, optimizing deployment for specific applications.
Enhanced APIs and Developer Productivity
JDK 9 introduces several API improvements to streamline development. Simon showcased factory methods for collections, allowing developers to create immutable collections with concise syntax, such as List.of() or Set.of(). The Streams API has been enhanced with methods like takeWhile, dropWhile, and ofNullable, improving expressiveness in data processing. Additionally, the introduction of jshell, an interactive REPL, enables rapid prototyping and experimentation. These enhancements reduce boilerplate code and enhance developer productivity, making Java more intuitive and efficient for modern application development.
JVM Internals and Performance
Simon delved into JVM enhancements, including improvements to the G1 garbage collector, which is now the default in JDK 9. The G1 collector offers better performance for large heaps, addressing limitations of the Concurrent Mark Sweep collector. Other internal improvements include a new process API for accessing operating system process details and a directive file for controlling JIT compiler behavior. These changes enhance runtime efficiency and provide developers with greater control over JVM performance, ensuring Java remains competitive for high-performance applications.
Housekeeping and Deprecations
JDK 9 includes significant housekeeping changes to streamline the platform. Simon highlighted the new version string format, adopting semantic versioning (major.minor.security.patch) for clearer identification. The directory structure has been flattened, eliminating the JRE subdirectory and tools.jar, with configuration files centralized in the conf directory. Deprecated APIs, such as the applet API and certain garbage collection options, have been removed to reduce maintenance overhead. These changes simplify the JDK’s structure, improving maintainability while requiring developers to test applications for compatibility.
Standards and Specialized Features
Simon also covered updates to standards and specialized features. The HTTP/2 client, introduced as an incubator module, allows developers to test and provide feedback before it becomes standard. Other standards updates include support for Unicode 8.0 and the deprecation of SHA-1 certificates for enhanced security. Specialized features, such as the annotations pipeline and parser API, improve the handling of complex annotations and programmatic interactions with the compiler. These updates ensure Java aligns with modern standards while offering flexibility for specialized use cases.