A JAR file allows Java runtimes to efficiently deploy a set of classes and their associated resources. The elements in a JAR file can be compressed, which, together with the ability to download an entire application in a single request, makes downloading a JAR file much faster than separately downloading the many uncompressed files which would form a single Java Application. The package java.util.jar contains classes that read and write JAR files.

A JAR file allows Java runtimes to efficiently deploy a set of classes and their associated resources. The elements in a JAR file can be compressed, which, together with the ability to download an entire application in a single request, makes downloading a JAR file much faster than separately downloading the many uncompressed files which would form a single Java Application. The package java.util.jar contains classes that read and write JAR files.