Java Archive

Type of format	File archive, data compression
First released	1997
Developer	Sun Microsystems
Filename extension	.jar
Open Format?	Yes
Free Format?	Yes
Magic Number	50 4b 03 04 "PK♥♦"

 A JAR (Java archive) file is a package file format used to aggregate many Java class files, associated metadata and resources (text, images, etc.) into one file for distribution for a BD-J application.

The Blu-ray specification requires an BD-J application (Xlet) to be contained in a JAR. An Xlet is a BD-J equivalent to an Applet. A single BD can have many JAR files, each for each BD-J Xlet, but only one JAR file is executed at a time. The maximum storage is 4 MB, however, assets and resources can be stored (and also shared) outside of the JAR file.

A JAR file is essentially a ZIP file with an optional META-INF directory; JARs may contain a manifest file, that is located at META-INF/MANIFEST.MF Within the META-INF directory, a manifest file (MANIFEST.MF) has a main section and a list of sections for individual JAR file entries. The entries in the manifest file describe how to use the JAR file.

Since it's based on the ZIP file format, everything inside the JAR file is compressed for faster loading times into the memory.

Author(s) : Æ Firestone