"java --module" - Launching Program from Module

Java Tools Tutorials - Herong's Tutorial Examples

∟"java --module" - Launching Program from Module

This section provides a tutorial example on how to use 'java --module' command to launch a program that is packaged in a Java module.

If your Java program is packaged in a Java module (which was introduced in Java 9 in 2017), you can launch your program using the "java --module" command.

Launch a program requires you to specify the program main class name with module name as a prefix.

For example, I have a program class called HelloModularized.java packaged in a Java module called com.herongyang. Here is the source file directory structure of the module:

herong> tree /F .\src
.\SRC
|---com.herongyang
    |   module-info.java
    |
    |---com
        |---herongyang
            |---util
                    HelloModularized.java

I used the following command to compile my module "com.herongyang":

herong> javac --module com.herongyang -d .\cls --module-source-path .\src

Here is the module class file directory structure generated by the above "javac" command:

herong> tree /F .\cls
.\CLS
|---com.herongyang
    |   module-info.class
    |
    |---com
        |---herongyang
            |---util
                    HelloModularized.class

Here is how I used the "java --module" command to launch my program:

herong> java --module-path .\cls \
   --module com.herongyang/com.herongyang.util.HelloModularized

Hello world! - Modularized

Cool. "java --module" command works! Note that:

The program class name must be prefixed with the module name "com.herongyang" and followed by the delimiter "/".
Module name "com.herongyang" is independent of the class package name "com.herongyang.util". I can use "herong" as the module name if I want to.
"--module-path" option is needed to tell "java" where to find the module class directory tree.

"--module-path" option must be specified before "--module" option. Otherwise, you will get the "Module ... not found" exception:

herong> java --module com.herongyang/com.herongyang.util.HelloModularized \
   --module-path .\cls

Error occurred during initialization of boot layer
java.lang.module.FindException: Module com.herongyang not found

You can still launch a program in a module as a class. You just need to specify the class path to the module sub-directory:

herong> java -classpath .\cls\com.herongyang \
   com.herongyang.util.HelloModularized

Hello world! - Modularized

Table of Contents

About This Book

Java Tools Terminology

Java Tools Included in JDK

javac - The Java Program Compiler

►java - The Java Program Launcher

java - Program Launching Command and Options

Launching Hello.java - My First Java Program

"java -classpath" - Specifying Class Path

"java -jar" - Specifying Executable JAR File

"java -X" - Specifying Non-Standard Options

"java --list-modules" - Listing Modules in JDK

"java --describe-module" - Printing Module Definition

►"java --module" - Launching Program from Module

"java --module" - Launching Program from Module JAR

javaw - Launching Java Programs without Console

jar - The JAR File Tool

jlink - The JRE Linker

jmod - The JMOD File Tool

jimage - The JIMAGE File Tool

jpackage - Binary Package Builder

javadoc - The Java Document Generator

jdeps - The Java Class Dependency Analyzer

jdeprscan - The Java Deprecated API Scanner

jdb - The Java Debugger

jcmd - The JVM Diagnostic Tool

jconsole - Java Monitoring and Management Console

jstat - JVM Statistics Monitoring Tool

JVM Troubleshooting Tools

jhsdb - The Java HotSpot Debugger

jvisualvm (Java VisualVM) - JVM Visual Tool

jmc - Java Mission Control

javap - The Java Class File Disassembler

keytool - Public Key Certificate Tool

jarsigner - JAR File Signer

jshell - Java Language Shell

jrunscript - Script Code Shell

Miscellaneous Tools

native2ascii - Native-to-ASCII Encoding Converter

JAB (Java Access Bridge) for Windows

Archived Tutorials

References

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