| jbx | Music Ace 2 Jukebox Data |
| jbx | Project Scheduler JBX Data |
| jc | CelLab Compiled Rule |
| jc | FlashGet Partial Download |
| jc1 | FlashGet Partial Download |
| jcamp | JCAMP-DX Format Data |
| jcd | FlashGet Download Database |
| jceks | Java Cryptography Extension KeyStore |
| jch | CelLab Population History Log |
| jcn | JobClock.NET TimeSummit Data |
| jcp | CelLab Pattern Data |
| jcp | Microsoft Exchange ESE Checkpoint File |
| jcrypt | JCrypt Data |
| jcsk | JetCast Skin Data |
| 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 | Oracle Documaker GenData Rules 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 |