File extensions start with character 'J'
| File Type | Category | File Format | |
|---|---|---|---|
| .j | Development Files | Java Source File | |
| .jad | Multiple Use Files | Java Application Descriptor File | |
| .jam | CAD Files | Jam STAPL File | |
| .jar | Program Execution Files | Java Archive File | |
| .jasper | Data Files | JasperReports Data File | |
| .jav | Development Files | Java Source File | |
| .java | Development Files | Java Source Code File | |
| .jbi | Data Files | Motoman Robot Job File | |
| .jdb | Data Files | Symantec Endpoint Protection Update File | |
| .jdc | Backup Files | JDownloader Links File | |
| .jef | Data Files | Janome Embroidery Format | |
| .jfif | Raster Graphics Files | JPEG File Interchange Format | |
| .jgz | Compressed Files | Gzipped Javascript File | |
| .jic | Compressed Files | Java Icon File | |
| .jis | Text Files | Japanese Industry Standard Text | |
| .jmp | Data Files | JMP Data File | |
| .jnilib | Development Files | JNI Library | |
| .jnlp | Java Files | Java Web Start File | |
| .jnt | Microsoft Files | Windows Journal File | |
| .jo | Audio Files | jo Audio File | |
| .joined | Data Files | HJ-Split Data File | |
| .jp1 | Text Files | Japanese (Romaji) Text File | |
| .jp2 | Raster Graphics Files | JPEG 2000 Core Image File | |
| .jpc | Raster Graphics Files | JPEG 2000 Code Stream File | |
| .jpd | Development Files | Java Process Definition | |
| .jpeg | Raster Graphics Files | JPEG Image | |
| .jpg | Raster Graphics Files | JPEG Image | |
| .jpg2 | Raster Graphics Files | JPEG 2000 Image | |
| .jpgw | Graphics Files | JPEG World File | |
| .jps | Raster Graphics Files | Stereo JPEG Image | |
| .jrprint | Data Files | JasperReports Print File | |
| .jrtf | Text Files | JAmes OS Rich Text File | |
| .jrxml | Data Files | JasperReports Layout File | |
| .js | JavaScript Files | JavaScript File | |
| .jse | Program Execution Files | JScript Encoded File | |
| .json | JavaScript Files | JavaScript Object Notation File | |
| .jsp | Java Files | Java Server Page | |
| .jsx | Program Execution Files | ExtendScript Script File | |
| .jude | Data Files | JUDE Project File | |
| .jws | Java Files | Java Web Services File |