Java 9 & Jigsaw: Reinhold on 'the State of the Modular System'

The first early access builds of JDK 9 with Project Jigsaw, the initiative that's bringing modularity to the Java platform, are now available for download. Before you jump in, you should definitely read Mark Reinhold's rich and readable "The State of the Module System," which he published online earlier this month. The chief architect of Oracle's Java Platform Group calls it "an informal overview of enhancements to the Java SE Platform prototyped in Project Jigsaw and proposed as the starting point for JSR 376."

JSR 376 is, of course, the Java Specification Request that aims to define "an approachable yet scalable module system for the Java Platform." But Project Jigsaw actually comprises JSR 376 and four JEPs (JDK Enhancements Proposals), which are sort of like JSRs that allow Oracle to develop small, targeted features for the Java language and virtual machine outside the Java Community Process (JCP). (The JCP requires full JSRs.) JEP 200: The Modular JDK defines a modular structure for the JDK. Reinhold has described it as an "umbrella for all the rest of them." JEP 201: Modular Source Code reorganizes the JDK source code into modules. JEP 220: Modular Run-Time Images restructures the JDK and JRE run-time images to accommodate modules. And the recently proposed JEP 260: Encapsulate Most Internal APIs (which I wrote about earlier), which Reinhold proposed to encapsulate unsupported, internal APIs, including sun.misc.Unsafe, within modules that define and use them.

The early access builds of Java 9 with Jigsaw include the latest prototype implementation of JSR 376 and the JDK-specific APIs and tools described in JEP 261, which will actually implement the changes and extensions to the Java programming language, JVM and standard Java APIs proposed by the JSR.

In his "state of" report, Reinhold provides a nuts-and-bolts breakdown of modularization, from the essential goals of the JSR, to detailed descriptions of modularization in the context of Java -- everything from "modules," "module artifacts" and "module descriptors" to the concepts of "readability," "accessibility" and "reflection."

In his conclusion, he writes:

"The module system described here has many facets, but most developers will only need to use some of them on a regular basis. We expect the basic concepts of module declarations, modular JAR files, module graphs, module paths, and unnamed modules to become reasonably familiar to most Java developers in the coming years. The more advanced features of qualified exports, increasing readability, and layers will, by contrast, be needed by relatively few."

He labeled the post "Initial Edition," so I'm expecting updates. I'd keep an eye out.

The long-awaited, much-delayed modularization of Java is going to be the biggest change since Java 8's support of lambdas. In a recent ADTmag post ("Is Oracle Dumping Its Java Evangelists?"), I followed up on a tweet by Gartner analyst Eric Knipp, who called Java a "dead platform." He made the case to me that Java is no longer the default choice for greenfield applications, and that change augurs its eventual demise. But I ran into Forrester analyst John R. Rymer at the recent Dreamforce event, and he posed the question, given all the recent and coming changes to Java -- especially modularization -- is it really the same language?

Posted by John K. Waters on September 23, 2015