Introduction to new features of Java8 (III.)

5. New Java Tools

Java 8 also brings a number of new command-line tools. In this section we will introduce the most interesting parts of them.

5.1 Nashorn Engine: JJS

JJS is a command-line tool based on the Nashorn engine. It accepts some JavaScript source code as parameters, and executes the source code. For example, we create a func.js file with the following content:

function f() {       return 1; }; print( f() + 1 );

We can pass this file as a parameter to JJS so that the file can be executed at the command line: JJS Func.js

The following is the output of the program on the console: 2

For more information, please refer to the official documentation

Class 5.2 Dependency Analyzer Jdeps

Jdeps is a useful command-line tool. It can display the package-level or class-level dependencies of a Java class. It accepts A. class file, a directory, or a jar file as input. The jdeps default outputs the results to the system output (console).

Let's look at the dependency report for the more popular spring Framework class libraries at this stage, to simplify this example, we only parse one jar file:org.springframework.core-3.0.5.release.jar

Jdeps Org.springframework.core-3.0.5.release.jar

This command outputs a lot of content, so here we only select a small part. Dependency information is grouped by package name. If the dependency is not in classpath, then the not foundis displayed.

org.springframework.core-3.0.5.RELEASE.jar -> C:\Program Files\Java\jdk1.8.0\jre\lib\rt.jar     org.springframework.core (org.springframework.core-3.0.5.RELEASE.jar)        -> java.io                                                   -> java.lang                                                 -> java.lang.annotation                                      -> java.lang.ref                                             -> java.lang.reflect                                         -> java.util                                                 -> java.util.concurrent                                      -> org.apache.commons.logging                         not found        -> org.springframework.asm                            not found        -> org.springframework.asm.commons                    not found     org.springframework.core.annotation (org.springframework.core-3.0.5.RELEASE.jar)        -> java.lang                                                 -> java.lang.annotation                                      -> java.lang.reflect                                         -> java.util

For more information, please refer to the official documentation

6. New features of the Java Virtual Machine (JVM)

PermGen space was removed and replaced by Metaspace (JEP 122). JVM Options -xx:permsize and -xx:maxpermsize are -xx:metaspacesize and -xx:maxmetaspacesize respectively Replaced.

7. Summary

More Outlook: Java 8 advances this great platform by releasing features that add to the productivity of programmers. It is still too early to move the production environment to Java 8, but it will be slowly accepted by the public over the next few months. Without a doubt, it's time to make your code compatible with Java 8 and migrate to Java 8 when Java 8 is secure enough.

As a community endorsement of Java 8, pivotal recently released a spring Framework 4.0.3 that can support Java 8 in a production environment.

We welcome your comments on the exciting features in Java 8!

Introduction to new features of Java8 (III.)