Differences between JAR file and module can be summarized in following points:
| JAR | Module |
| JAR stands for Java Archive and is a file format based on the ZIP file format. It is used for aggregating many files and associated metadata and resources(text, images etc) into one file to distribute as a library or application software. | Modules is a language feature introduced in Java 9. Module is a group of packages and has information about module dependencies and types it exports to other modules. This information is saved in module-info.java file. |
| JAR file does not provide information about dependencies on other JAR files. | A module can define dependency on other modules using module-info.java file. |
| Using a JAR file may result in NoClassDefFoundError error as there is no way to check if all dependencies are met before execution. | While working with modules, JVM checks for all module dependencies at the beginning of execution. So there is no possibility to get NoClassDefFoundError during execution. |
| JAR is not a programming feature and is not related to application design as such. | Module is a programming feature and is related to the design of application. |
| JAR does not impact encapsulation of types it contains. public types are available for all types outside JAR file. | Module enhances strong encapsulation of types it contains. public is not so much public in case of types in modules. |
| JAR does not define what types it holds are available for other types (outside the JAR). | Module defines which types(it contains) are accessible and which types are not. |
| JAR has no impact in reducing the size of distributed software. | Module helps in reducing the size of distributed software and thus helps developing applications for small devices. |
| JAR is used to aggregate files. So, name of JAR can be changed easily as long as JVM classloader is able to find class. | The name of a module can be explicitly referenced in the declaration of other modules, so name of module can not be changed easily. |