| Extension |
File Type |
File Description |
| .j | Developer | Java Source File (Most common) |
| .j2c | Raster Image | JPEG 2000 Code Stream |
| .j2i | Game | Jazz 2 Internet Link File |
| .j2k | Raster Image | JPEG 2000 Image |
| .j2l | Game | Jazz Jackrabbit 2 Level File |
| .jad | Misc | Java Application Descriptor File |
| .jam | Audio | JAM Musical Score (Most common) |
| .jar | Executable | Java Archive File |
| .jas | Raster Image | Paint Shop Pro Compressed Graphic |
| .jav | Developer | Java Source File |
| .java | Developer | Java Source Code File |
| .jbf | Image | Paint Shop Pro Browser Cache |
| .jbig | Image | Joint Bi-level Image Group File |
| .jbk | Backup | Juno Backup File |
| .jbr | Raster Image | Paint Shop Pro Brushes File |
| .jc | Misc | FlashGet Partial Download |
| .jc! | Misc | FlashGet Incomplete Download |
| .jcz | Web | Liquid Motion Animation |
| .jed | Developer | Xilinx JEDEC Programming File |
| .jef | Data | Janome Embroidery Format |
| .jfi | Image | JPEG File Interchange |
| .jfif | Raster Image | JPEG File Interchange Format |
| .jg4 | Game | BigJig Jigsaw Puzzle |
| .jgz | Compressed | Gzipped Javascript File |
| .jhtml | Web | Java HTML Web Page |
| .jia | Raster Image | Digital Photo Navigator Album |
| .jic | Compressed | Java Icon File (Most common) |
| .jif | Raster Image | JPEG Image File |
| .jiff | Raster Image | JPEG Image File Format |
| .jis | Text | Japanese Industry Standard Text |
| .jng | Raster Image | JPEG Network Graphic |
| .jnlp | Web | Java Web Start File |
| .jp1 | Text | Japanese (Romaji) Text File |
| .jp2 | Raster Image | JPEG 2000 Core Image File |
| .jpc | Image | JPEG 2000 Code Stream File |
| .jpd | Developer | Java Process Definition (Most common) |
| .jpe | Raster Image | JPEG Image |
| .jpeg | Raster Image | JPEG Image File |
| .jpf | Raster Image | JPEG 2000 Image |
| .jpg | Raster Image | JPEG Image File |
| .jph | Data | JProbe Memory Snapshot |
| .jpr | Developer | JBuilder Project |
| .jpw | Image | World File for JPEG |
| .jpx | Raster Image | JPEG 2000 Image File (Most common) |
| .jrs | Misc | Exchange Reserve Transaction Log File |
| .js | Web | JavaScript File (Most common) |
| .jse | Executable | JScript Encoded File |
| .json | Developer | JavaScript Object Notation File |
| .jsp | Web | Java Server Page |
| .jspa | Web | Java Servlet Alias |
| .jspx | Web | XML Java Server Page |
| .jsx | Executable | ExtendScript Script File |
| .jt | Image | JT Open CAD File |
| .jtf | Raster Image | JPEG Tagged Interchange Format |
| .jude | Data | JUDE Project File |
| .jvs | Web | JavaScript Proxy Autoconfig File |
| .jws | Web | Java Web Services File (Most common) |
