Java Module System

The Java Module System specifies a distribution format for collections of Java code and associated resources. It also specifies a repository for storing these collections, or modules, and identifies how they can be discovered, loaded and checked for integrity. It includes features such as versioning and namespaces with the aim of fixing some of the shortcomings in the existing JAR format, especially the JAR Hell, which can lead to issues such as classpath and class loading problems.

The Java Module System was initially being developed under the Java Community Process as JSR 277 and was scheduled to be released with Java 7.

JSR 277 later was put on hold and Project Jigsaw was created to modularize the JDK. This JSR was superseded by JSR 376 (Java Platform Module System).

Project Jigsaw was originally intended for Java 7 (2011) but was deferred to Java 8 (2014) as part of Plan B, and again deferred to a Java 9 release in 2016.

Architecture

The Java Module System implemented for Java 9 will include the following JEPs and JSR (Java Specification Request):

Modular programming

Modular programming is a software design technique that emphasizes separating the functionality of a program into independent, interchangeable modules, such that each contains everything necessary to execute only one aspect of the desired functionality.

A module interface expresses the elements that are provided and required by the module. The elements defined in the interface are detectable by other modules. The implementation contains the working code that corresponds to the elements declared in the interface. Modular programming is closely related to structured programming and object-oriented programming, all having the same goal of facilitating construction of large software programs and systems by decomposition into smaller pieces, and all originating around the 1960s. While historically usage of these terms has been inconsistent, today "modular programming" refers to high-level decomposition of the code of an entire program into pieces, structured programming to the low-level code use of structured control flow, and object-oriented programming to the data use of objects, a kind of data structure.