Motivation

The Joy of Java 11 is finally upon us. Here’s why you should drop everything you’re doing and upgrade.

• Java 8 is going through its End of Public Updates process (Jan 2019)
• Java 11 is the next LTS release
• The accumulation of new features across the last 3 versions is substantial
• The move to shorter release schedule and the java module system represents a major shift in the ecosystem
• This shift will take a while to fully implement, so it’s preferable to start early
• Upgrading to Java 11 puts you on firm and stable ground while making sure you don’t stagnate

Features

• Module System (Project Jigsaw, JPMS)
• Java 9 REPL (jshell)
• Local variable type inference (var)
• Private methods in interfaces
• Reactive streams
• Improvements to collection factory methods, stream api, process api, try with resources, optional class, string class
• Custom runtime images (jlink)
• Single file source code programs
• Improvements to the GC and the JIT compiler

Module System

Modularizing existing projects is not required but recommended.

• The JPMS is a fundamental change in how java programs are built and run
• Replaces the error-prone class-path with a module-path
• Provides strong encapsulation:
  • Packages are now organized into modules
  • Modules need to declare what they export and what they depend on
• The jdeps tool: used to detect dependencies between jars
• The unnamed module: bottom-up migration
  • Automatically depends on all named modules
  • Cannot be depended upon
• Automatic modules: top-down migration
  • Allows modules to depend on un-modularized jars by treating them as automatic modules
  • Two or more jars on the class-path can’t contain types in the same package

Resources

• Oracle - migration guide
• DZone - intro to modules
• Romexsoft - migration guide