Definition: extension J

 Ext.  Type of file

 J2K   JPEG 2000

 JAVA  Java source code

 JFF   JPEG bitmap

 JIF   JPEG bitmap

 JP2   JPEG 2000
 JPE   JPEG (alternate extension)
 JPG   JPEG bitmap

 JS    JavaScript
 JSP   JavaServer Page

 JT    JT Fax
 JTF   JPEG bitmap