In summary, the strategy is:
- Module names must be valid Java identifiers! ...
- Module names must be reverse-DNS, just like package names, e.g. ...
- Modules are a group of packages. ...
- Module names are strongly recommended to be the same as the name of the super-package.
- Creating a module with a particular name takes ownership of that package name and everything beneath it.
How should I name a Java module?
It is recommended to name a Java module the same as the name of the root Java package contained in the module - if that is possible (some modules might contain multiple root packages).
What is the difference between a Java module and a module?
A Java module must explicitly tell which Java packages inside the module are to be exported (visible) to other Java modules using the module. A Java module can contain Java packages which are not exported. Classes in unexported packages cannot be used by other Java modules.
What is --module-path and --add-modules in Java?
The --module-path argument specifies the module paths to look for modules in. The example above sets the out directory into which we have previously compiled our module, and the jmods directory of the JDK installation. The --add-modules argument specifies the Java modules to package into the standalone application.
What should the name of a module's name be?
A module's name should correspond to the name of its principal exported API package, which should also follow that convention.
What is module info.java?
What is the name of the module declaration?
What is lib module?
What is a module path?
How to launch a modular app?
What does module resolution do?
Does com.example.app depend on java.sql?
See 2 more
What is module name in Java project?
A Java module name follows the same naming rules as Java packages. However, you should not use underscores ( _ ) in module names (or package names, class names, method names, variable names etc.)
What is module name in Java Eclipse?
Java 9 Module System has a "java. base" Module which is an independent module. There are many UI features supported in Eclipse to help the Java programmers use Java Modules. In the Eclipse IDE, a modular Java Project can be created using the New Java Project Menu which has by default Create module-info.
What is a named module?
Module Declarations. As we mentioned, a module must provide a module descriptor—metadata that specifies the module's dependencies, the packages the module makes available to other modules, and more. A module descriptor is the compiled version of a module declaration that's defined in a file named module-info.
What are modules in Java 9?
Defining the Java 9 module. A module is a collection of code, data, and resources. It is a set of related packages and types (classes, abstract classes, interfaces, and more) with code, data files, and some static resources. For example, the module descriptor module-info.
Where is Java module-info?
The module declaration ( module-info. java ) needs to go into your source root directory (e.g. src/main/java ). It then has to be among the list of files to compile, so it will get turned into a module descriptor ( module-info. class ).
How do you create a Java module?
Develop the modules componentsRight-click the module source folder, then New module-info.java ; an empty module descriptor is created with a default module name as shown here:To create a new package, right-click the src folder, click New, and then click Package.Enter the package name ( eg.More items...•
What is a module in coding?
In computer software, a module is an extension to a main program dedicated to a specific function. In programming, a module is a section of code that is added in as a whole or is designed for easy reusability.
How do I install a Java module?
Our plan:Step 1: Download Java 9 from scratch and install.Step 2: Concept: Describe our module filename.Step 3: Concept: Describe our module filepath.Step 4: Code our module descriptor file: module-info. java.Step 5: Add code to our module.Step 6: Compile our module.Step 7: Run our module.
What is the difference between module and package in Java?
A module is a collection of related Java packages and associated resources with a descriptor file, which contains information about which packages/resources are exposed by this module, which packages are used by current module and some other information.
How do I use Java 9 modules?
Creating ModuleCreate a folder C:\>JAVA\src. Now create a folder com. tutorialspoint. ... Create module-info. java in C:\>JAVA\src\com. ... Add the source code in the module. Create Java9Tester. ... Create a folder C:\>JAVA\mods. Now create a folder com. ... Let's run the module to see the result. Run the following command.
Does Java 8 have modules?
Java 8 with Project Jigsaw brings a module system to the SDK. I see it as a good thing as it's part of the package (built-in). OSGi also provides a module system, but requires a container.
What is module in project?
A module is a collection of source files and build settings that allow you to divide your project into discrete units of functionality. Your project can have one or many modules, and one module may use another module as a dependency.
What is module info Java?
module-info. java file. It declares the dependencies within the module system and allows the compiler and the runtime to police the boundaries/access violations between the modules in your application.
What is module path in Eclipse?
A ModulePath is a sequence of Modules (which are provided in a Folder format or JAR format). If a Module is in folder format, that means it is in Module format. If it is in a JAR format, that jar is known as “Modular JAR“.
How do modules work in Eclipse?
1. Goals :Create Module 1 EM–Common :Create Module 2 EM–Service :Step 1 : In eclipse select File -> New -> Java Project.Step 2 : In project creation window enter Project name EM-Common -> select JRE version as Java SE 9.Step 3 : Add new source folder to the project. ... Step 4 : Enter folder name and click on finish.More items...•
How do I start a new Java project in Eclipse?
Step 2: How to create a new projectChoose File -> New -> Project from the Eclipse menu bar, as in the following example:The New Project wizard will appear, as in the following example:Make sure "Java Project" is selected and click the Next button. ... Congratulations, you have created your first Java project!
What is a module in Java?
A Java module is one or more Java packages that belong together. A module could be either a full Java application, a Java Platform API, or a third party API.
What is a Java module?
A Java module is a packaging mechanism that enables you to package a Java application or Java API as a separate Java module. A Java module is packaged as a modular JAR file . A Java module can specify which of the Java packages it contains that should be visible to other Java modules which uses this module.
What is the root directory of a Java module?
The module root directory is used both for the source files and compiled classes of a Java module. That means, that if your Java project has a source root directory named src/main/java - then each module inside your project will have its own module root directory under src/main/java. For instance:
How to compile a module in Java?
In order to compile a Java module you need to use the javac command that comes with the Java SDK. Remember, you need Java 9 or later to compile a Java module.
What is a Java package?
A Java module can contain Java packages which are not exported. Classes in unexported packages cannot be used by other Java modules. Such packages can only be used internally in the Java module that contains them. Packages that are not exported are also referred to as hidden packages, or encapsulated packages.
Where is the module info.java located?
Each Java module needs a Java module descriptor named module-info.java which has to be located in the corresponding module root directory. For the module root directory src/main/java/com.jenkov.mymodule the path to the module's module descriptor will be src/main/java/com.jenkov.mymodule/module-info.java .
Where are Java classes nested?
Before Java 9 all Java classes for an application or API were nested directly inside a root class directory (which was added to the classpath), or directly inside a JAR file. For instance, the directory structure for the compiled packages of com.jenkov.mymodule would look like this:
What is JPMS in Java?
In this article, I introduce the Java 9 Platform Module System (JPMS), the most important new software engineering technology in Java since its inception. Modularity—the result of Project Jigsaw —helps developers at all levels be more productive as they build, maintain, and evolve software systems, especially large systems.
What is the key motivation of the module system?
A key motivation of the module system is strong encapsulation.
What is modularity in language?
Modularity adds a higher level of aggregation above packages. The key new language element is the module —a uniquely named, reusable group of related packages, as well as resources (such as images and XML files) and a module descriptor specifying
How long has Java SE been around?
The Java SE platform has been around since 1995. There are now approximately 10 million developers using it to build everything from small apps for resource-constrained devices—like those in the Internet of Things (IoT) and other embedded devices—to large-scale business-critical and mission-critical systems. There are massive amounts of legacy code out there, but until now, the Java platform has primarily been a monolithic one-size-fits-all solution. Over the years, there have been various efforts geared to modularizing Java, but none is widely used—and none could be used to modularize the Java platform.
How to specify a dependency on another module?
To specify a dependency on another module, use requires, as in: requires modulename; There is also a requires static directive to indicate that a module is required at compile time, but is optional at runtime . This is known as an optional dependency and won’t be discussed in this introduction.
Is Java scalable?
Scalable Java platform—Previously, the Java platform was a monolith consisting of a massive number of packages, making it challenging to develop, maintain and evolve. It couldn’t be easily subsetted. The platform is now modularized into 95 modules (this number might change as Java evolves). You can create custom runtimes consisting of only modules you need for your apps or the devices you’re targeting. For example, if a device does not support GUIs, you could create a runtime that does not include the GUI modules, significantly reducing the runtime’s size.
Does Java SE have implied readability?
Also, though a Java SE standard module may depend on non-standard modules, it must not grant implied readability to them.
What is module system in Java?
Java Module System is a major change in Java 9 version. Java added this feature to collect Java packages and code into a single unit called module. In earlier versions of Java, there was no concept of module to create modular Java applications, that why size of application increased and difficult to move around.
Why did Java 9 restructure?
To deal with situation, Java 9 restructured JDK into set of modules so that we can use only required module for our project.
Why is JDK and JRE reconstructed?
The JDK and JRE both are reconstructed to accommodate modules. It improves performance, security and maintainability.
What should a module name start with?
Choose module names that start with the name of your project or product. Module (and package) names that start with reversed domain names are less likely to conflict but they're unnecessarily verbose, they start with the least-important information (e.g., com, org, or net ), and they don't read well after exogenous changes such as open-source donations or corporate acquisitions (e.g., com.sun.* ).
What should a module's name be?
A module's name should correspond to the name of its principal exported API package, which should also follow that convention. If a module does not have such a package, or if for legacy reasons it must have a name that does not correspond to one of its exported packages, then its name should at least start with the reversed form of an Internet domain with which the author is associated.
Why are module names not unique?
The JDK team stated that module names may not have to be unique after all "because modules are more abstract than the artifacts that define them". Mark Reinhold writes: Choose module names that start with the name of your project or product.
Can a module name not include a domain?
Also, having module names that do not include a domain would allow exchanging that module against another implementation as long as it has the same name (and implements the same public API of course).
What is module info.java?
It is a file with name module-info.java, under the root module path. This file contains the module metadata information.
What is a base module in Java 9?
In Java 9 ‘java.base’ is a base module. It does not depend on any other modules. By default, all modules including user defined modules are dependent on this module. Even if we do not specify ‘java.base’ module, it will be imported automatically.
What are theModule types?
Depending on how the modules are used, they are categorised into 4 types,
What is the use keyword in Java?
Using uses keyword we can specify that our module needs or consumes some service. Service is a interface or abstract class. It should not be an implementation class.
What keyword is used to import a module?
If a module needs to access packages exported from other modules, then these other modules must be imported using ‘requires’ keyword.
What is an unnamed module?
Unnamed Module: jars and classes added into the classpath. When we add jar or class to the classpath all these classes are added to the unnamed module. Only exports to other unnamed module and automatic module. This means, application modules cannot access these classes. It can access classes from all the modules.
How to list jmods?
We can list system modules or the contents of this ‘jmods’ folder by using the command : java –list-modules.
Question
It has been a long time since I touched Java and when updating to the latest version of both the environment (Eclipse) and the JDK, to version 12, it asks me when creating a project if I want to create a new module-info something that I had never before asked.
Answer
After searching the bibliography at my university, I found the answer to the question about what modules are and what is their usefulness.
What is module info.java?
The module declaration module-info.java is a source file like any other and so it takes a few steps before it's running in the JVM. Fortunately, these are the exact same steps that your source code takes and most build tools and IDEs understand that well enough to adapt to its presence. In all likelihood, you don't need to do anything manually to build and launch a modular code base. Of course there is value in understanding the nitty, gritty details, so a dedicated article takes you from source code to running JVM with just command line tools.
What is the name of the module declaration?
At the core of each module is the module declaration, a file with the name module-info.java that defines all properties of a module. As an example, here's the one for java.sql, the platform module that defines the JDBC API:
What is lib module?
The lib module uses Service, one of its own types, as a service and the app module, which depends on the lib module, provides it with MyService . At run time the lib module will then access all classes that implement / extend the service type by using the ServiceLoader API with a call as simple as ServiceLoader.load (Service.class) . That means the library module executes behavior defined in the app module even though it doesn't depend on it - that's great to untangle dependencies and keep modules focused in their concerns.
What is a module path?
The module path is a new concept that parallels the class path: It is a list of artifacts (JARs or bytecode folders) and directories that contain artifacts. The module system uses it to locate required modules that are not found in the runtime, so usually all app, library, and framework modules. It turns all artifacts on the module path into modules, even plain JARs, which get turned into automatic modules, which is enables incremental modularization . Both javac and java as well as other module-related commands understand and process the module path.
How to launch a modular app?
To launch a modular app, run the java command with a module path and a so-called initial module - the module that contains the main method:
What does module resolution do?
During module resolution, the module system checks whether all required dependencies, direct and transitive, are present and reports an error if something's missing. But it goes beyond just checking presence.
Does com.example.app depend on java.sql?
We can see that the app module com.example.app depends on the library com.example.lib, which in turn needs the unrelated module com.sample.other and the platform module java.sql . We don't have the declaration of com.sample.other but we know that java.sql depends on java.logging, java.transaction.xa, and java.xml . If we look those up, we see that they have no further dependencies. (Or rather, no explicit dependencies - check the section on the base module below for more details.)
What Is A Module?
- Modularity adds a higher level of aggregation above packages. The key new language element is the module—a uniquely named, reusable group of related packages, as well as resources (such as images and XML files) and a module descriptorspecifying 1. the module’s name 2. the module’s dependencies(that is, other modules this module depends on) 3. the p...
History
- The Java SE platform has been around since 1995. There are now approximately 10 million developers using it to build everything from small apps for resource-constrained devices—like those in the Internet of Things (IoT) and other embedded devices—to large-scale business-critical and mission-critical systems. There are massive amounts of legacy code out there, but until now…
Goals
- According to JSR 376, the key goals of modularizing the Java SE platform are 1. Reliable configuration—Modularity provides mechanisms for explicitly declaring dependencies between modules in a manner that’s recognized both at compile time and execution time. The system can walk through these dependencies to determine the subset of all modules required to support you…
Listing The Jdk’S Modules
- A crucial aspect of Java 9 is dividing the JDK into modules to support various configurations. (Consult “JEP 200: The Modular JDK.” All the Java modularity JEPs and JSRs are shown in Table 1.) Using the java command from the JDK’s bin folder with the --list-modulesoption, as in: lists the JDK’s set of modules, which includes the standard modules that implement the Java Language …
Module Declarations
- As we mentioned, a module must provide a module descriptor—metadata that specifies the module’s dependencies, the packages the module makes available to other modules, and more. A module descriptor is the compiled version of a module declaration that’s defined in a file named module-info.java. Each module declaration begins with the keyword module, followed by a uniqu…
Reflection Defaults
- By default, a module with runtime reflective access to a package can see the package’s public types (and their nested public and protected types). However, the code in other modules can access all types in the exposed package and all members within those types, including private members via setAccessible, as in earlier Java versions. For more information on setAccessible …