Updating a jar
The file extension was developed by Sun Microsystems.
Files with the extension are compressed files that use the ZIP format in order to compress Java files.
The files with the extension contain Java classes and metadata.
JAR files are often used by programs like Thunderbird, Firefox and Sea Monkey to store program add-ons and program themes.
JAR files can also be created to store files, much in the same way ZIP files are used.
Files with the extension can contain multiple files that have been compressed into a single folder or one large file that has been compressed to achieve a more manageable file size.
Usually these file are used for archiving and distribution the files and implementing various libraries, components and plug-ins in java applications.
Compiler and JVMs (Java Virtual Machine) can understand and implement these formats for java application.