| 41. | .jsm | Jigsaw file (JugWin) |
| 42. | .jsp | A HTML page containing a reference to a Java servlet |
| 43. | .jss | Jigsaw file (JugWin) |
| 44. | .jtf | Bitmap graphics (JPEG Tagged Interchange Format) ◊ Fax (Hayes JT Fax) ◊ JPEG bitmap |
| 45. | .jtif | Bitmap graphics (JPEG Tagged Interchange Format) |
| 46. | .jtk | Java ToolKit file (Sun Microsystems) |
| 47. | .jut | Jutvision Scene (Jutvision) |
| 48. | .jw | Text document (JustWrite) |
| 49. | .jwl | CD disc case (Jewel Case Creator) ◊ Library (JustWrite) |
| 50. | .jzz | Spreadsheet (Jazz) |
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