1. Introduction
In this example, I would like to show you how to get started with Java 9 and write a simple Hello World program. Here, I present a simple example to get started along with details of some of the important new features.
Table Of Contents
Java 9 is a major release. At the time of writing of this article, JDK 9 is currently available for early access download on the oracle site and is expected to be released on July 27, 2017. This document attempts to summarize details on how to get started with JDK 9 and some of the main features with this new release.
Complete list of features can be viewed at the oracle site.
2. Getting started
To download the currently available early access JDK or JRE 9, visit http://jdk.java.net/9/
As shown in the image above, at the site, accept the license agreement and proceed to the download section as shown below.
Please select the appropriate OS and option for 32/ 64 bits for the OS to download the JDK/ JRE. It is also recommended to download the documentation along with the JDK/ JRE installation.
3. Running a Hello World program on Java 9
The directory structure has changed in JDK 9. The below section lists the steps to get a simple Hello World program to run on JDK 9 via command line.
JDK 9 installation on my windows machine looks like the image above.
A sample Hello World program is listed below, do keep in mind that this is a legacy class and does not use the new module feature introduced in java 9.
HelloWorldJDK9.java
public class HelloWorldJDK9 {
public static void main(String[] args) {
System.out.println("Hello world");
}
}
To compile this class on the JDK 9 installed, run the below javac command. To run the generated class, use the regular java command or run the class using eclipse.
You may use eclipse or an IDE of your choice (may need installation of Java 9 support plugins).
4. Changes in Java 9 and new features
4.1 Version in class files
Verify the class file created in step 3 by running javap as shown below. The output of javap has major version listed (as highlighted in yellow). The version number for Java 9 compiled classes is 53 as against version 52 for Java 8 compiled classes.
4.2 Module system/ Jigsaw
Module system is one of the most important changes in Java 9. This provides an entirely new dimension to writing and deploying java code. JDK 9 has reorganized JDK and JRE into set of modules as well. With the new module system, application would consist of a number of modules.
Also, with the modularisation of JDK, source code has been restructured to make it easy to maintain. Class and resource files previously stored in lib/rt.jar and lib/tools.jar and other internal jars would be stored in different formats in the lib directory.
More details can be found at the open jdk sites for JEP 261, 200 and 220.
4.3 Deprecation of Applet API
With newer web browser technologies available, Oracle plans to deprecate the Applet API and it is recommended to rewrite applets as support may be removed in future release.
Alternatives for applets and embedded JavaFX applications include Java Web Start and self-contained applications. Details are available at this link.
4.4 HTML 5 javadocs
Java 9 will have support for creating javadocs in HTML 5 along with the existing HTML 4 support. Refer details at the jira for this change.
4.5 G1 as default Garbage Collector
Java 9 has made G1 the new default garbage collector. G1 is expected to provide overall performance improvement. Also, some GC combinations that were deprecated in Java 8 have been removed.
Refer JEP 214 for more details.
Here is a detailed summary of the flags and flag combinations that will stop working:
[box type=”shadow” ]DefNew + CMS : -XX:-UseParNewGC -XX:+UseConcMarkSweepGC
ParNew + SerialOld : -XX:+UseParNewGC
ParNew + iCMS : -Xincgc
ParNew + iCMS : -XX:+CMSIncrementalMode -XX:+UseConcMarkSweepGC
DefNew + iCMS : -XX:+CMSIncrementalMode -XX:+UseConcMarkSweepGC -XX:-UseParNewGC
CMS foreground : -XX:+UseCMSCompactAtFullCollection
CMS foreground : -XX:+CMSFullGCsBeforeCompaction
CMS foreground : -XX:+UseCMSCollectionPassing[/box]
5. Summary
This article is aimed at providing a starter to Java 9 and some important new features. JDK 9 has some exciting new features and promises to change how we currently write and deploy java code.
6. References
Oracle site has excellent details of the new JDK 9 features.
Java 9 is a major update to Java, which brings the language up to the state of development. It allows Java to make better use of more modern hardware and fixes lots of gaps in Java.
Great blog! Amazing features of Java 9 With work ongoing to move ahead on the next version of conventional Coffee, designers can start getting excited about what they will get with the organized update. Thanks for sharing with us, will look forward more from you!