are in unnamed module of loader app

Introduction

In the world of programming, modules are an essential component of building software. In Java, modules are a new addition to the language, and they have been introduced in JDK 9. The use of modules in Java allows developers to define and organize their code into small, manageable units. In this article, we will explore the concept of unnamed modules of the loader app in Java.

What are Unnamed Modules of the Loader App?

In Java, a module is a collection of related code that can be loaded, tested, and executed independently. There are two types of modules in Java: named and unnamed modules. A named module is a module that has a module-info.java file that specifies its name, dependencies and exports. An unnamed module, on the other hand, is a module that does not have a module-info.java file. Unnamed modules are created automatically when classes are loaded from the classpath and do not contain any module definition.The loader app is the part of the Java Virtual Machine (JVM) responsible for loading and initializing classes. When a class is loaded by the loader app, it is placed in the unnamed module of the loader app. This module is essentially a catch-all module that contains all the classes that are not defined in named modules.

How are Unnamed Modules used?

Unnamed modules serve as a bridge between the pre-module era and the module era in Java. Because the loader app cannot load classes from the classpath into named modules, all classes that are not explicitly defined in modules are loaded into the unnamed module.The unnamed module allows existing code to run on the module system without requiring any modification. This means that developers can gradually modularize their codebase without having to do everything at once. Any class that is not explicitly in a named module is placed in the unnamed module by default, which allows it to coexist with the modularized code.

Controlling Access to Unnamed Modules

Unnamed modules do not have an associated module definition, which means that they have no exports or requires clauses. This can cause issues when classes in the unnamed module attempt to access classes in named modules. In order to avoid these issues, the unnamed module employs a set of default rules for accessing classes in named modules.These rules allow classes in the unnamed module to access any class or package in any named module that is exported to the unnamed module. Additionally, the unnamed module is not allowed to access internal classes or resources of any named module. This helps to maintain the encapsulation and security of the named module system.

Conclusion

Java's module system is a powerful addition to the language that provides developers with a way to organize and maintain their codebase. The use of modules allows code to be broken down into small, manageable units that can be easily tested, maintained, and updated. Unnamed modules are an important part of the module system that allows existing code to coexist with modularized code without requiring any modification. Understanding how unnamed modules work and how they can be controlled is an important part of developing in Java's module system.