| jcv | Garmin City Navigator Junction View |
| jcw | JCreator Workspace |
| jd | Jigsaw Terminal Data |
| jd | Doclava Javadoc Template |
| jda | Winphone Fax Send Journal Data |
| jdb | Winphone Fax Receive Journal Data |
| jdbg | Embedded JCL Debug Info |
| jdc | JDownloader Container |
| jdd | Globus Toolkit Job Description Document |
| jdf | Job Definition Format File |
| jdl | gLite Job Description Language File |
| jds | JDataStore Database |
| jdsu | ACTIX Analyzer JDSU Data |
| jdt | Accelio Capture Classic Filler Data |
| jdx | JSpell Dictionary Data |
| jdx | JCAMP-DX Format Data |
| jeb | PENSIM Output |
| jed | Xilinx JEDEC Data |
| jedec | Xilinx JEDEC Data |
| jef | Janome Embroidery Data |
| jeff | Java Explanation Facility Framework Data |
| jem | Optifine JSON Entity Model |
| jet | California JET Data |
| jfd | FormWare Job Definition |
| jft | JetForm Job Ticket |
| jga | John GBC Saved State |
| jgd | Corel Paint Shop Pro Gradients Data |
| jgd | JVC Projectors Gamma Curve Data |
| jgl | QWS3270 PLUS Session Layout |
| jgp | QWS3270 PLUS Session Parameter File |
| jgs | QWS3270 PLUS Script File |
| jhd | WCAD01 Job Information Data |
| jhm | JavaHelp Map |
| jib | Sam2p JIB File |
| jjf | FlashJester Jugglor Data |