.JAR File

The jar file extension is mainly associated with Java and used for Java archives. The Java Archive (JAR) file format enables you to bundle multiple files into a single archive file.

Typically a jar file contains the class files and auxiliary resources associated with applets and applications.

The JAR file format provides many benefits:

Security: You can digitally sign the contents of a jar file. Users who recognize your signature can then optionally grant your software security privileges it wouldn't otherwise have.

Decreased download time: If your applet is bundled in a JAR file, the applet's class files and associated resources can be downloaded to a browser in a single HTTP transaction without the need for opening a new connection for each file.

Compression: The JAR format allows you to compress your files for efficient storage.

Packaging for extensions: The extensions framework provides a means by which you can add functionality to the Java core platform, and the JAR file format defines the packaging for extensions.

Java 3D and JavaMail are examples of extensions developed by Sun. By using the JAR file format, you can turn your software into extensions as well.

Package Sealing: Packages stored in *.jar files can be optionally sealed so that the package can enforce version consistency. Sealing a package within a jar file means that all classes defined in that package must be found in the same JAR file.

Package Versioning: A jar file can hold data about the files it contains, such as vendor and version information. Portability: The mechanism for handling *.jar files is a standard part of the Java platform's core API.

JAR has a similar command and option feature set to the PC Archiver ARJ, but it is not archive compatible with ARJ. JAR comes in a 16 bit DOS version and a 32 bit Windows version. This format is unrelated to the Sun JAR archive format.

MIME types:
application/java-archive
application/x-java-archive

A jar file extension is commonly used for Java archives, which often contain applets or applications. Used for java application distribution/installation purposes.

How to open:

You can launch the *.jar file with proper JRE installed.Winrar can open them as well... If you use a windows and you don't know what you are doing, dont try execute or opening these files with windows explorer!

How to convert:

You can probably extract the content of *.jar files with some archivers, like WinRAR or WinZip.