| .j | Java Source Code |
| .j2b | Jazz Jackrabbit 2 Music |
| .j2c | JPEG2000 Image Format |
| .j2d | Jazz Jackrabbit Data |
| .j2e | Jazz Jackrabbit 2 Episode |
| .j2i | Jazz Jackrabbit 2 Internet Server Link Format |
| .j2k | JPEG2000 Code Stream Image |
| .j2l | Jazz Jackrabbit 2 Level Format |
| .j2si | Jazz Jackrabbit 2 Internet Server Link |
| .j2w | ArcExplorer World |
| .j3o | JMonkeyEngine 3D Scene |
| .j6i | Ricoh Digital Camera Image |
| .ja | Jet Archive |
| .jac | JaStaCry Encrypted Format |
| .jacl | IBM WebSphere Server Script |
| .jad | Java Application Descriptor Format |
| .jade | Jade Programming Language Source Code |
| .jag | Jagex Data Format |
| .jai | Jaikoz Settings |
| .jam | Leisure Suit Larry Magna Cum Laude Archive Format |
| .jan | Janome Digitizer Embroidery Object |
| .jap | Japanese Nintendo 64 Game ROM |
| .jar | Compressed Archive Format Package For Java Classes And Data Format |
| .jar.pack | Oracle Pack200 Packed JAR Format |
| .jardesc | Eclipse JAR Settings |
| .jarvis | Jarvis Subscriber Format |
| .jas | Corel PaintShop Photo Pro Bitmap Graphics Format |
| .jasper | JasperReports Data Format |
| .jav | Java Language Source Code Format |
| .java | Java Language Source Code Format |
| .javajet | Eclipse JET Java Template |
| .jax | Java Executable JAR |
| .jb2 | JBIG2 Image Format |
| .jbc | Jam STAPL Byte-Code Format |
| .jbf | Corel PaintShop Photo Pro Image Browser Format |
| .jbg | Image JBIG 1-bit Raster |
| .jbi | Motoman Robot Job Format |
| .jbig | JBIG Raster Image Graphics |
| .jbig2 | JBIG2 |
| .jbk | Juno Backup Format |
| .jbl | Doom Scene Add-on |
| .jbmp | JAmes OS Bitmap Image |
| .jbr | Corel PaintShop Photo Pro Brushes Format |
| .jbt | JAWS |
| .jc | FlashGet Partial Download Format |
| .jc! | FlashGet Incomplete Download Format |
| .jcc | Code Crusader Project Data |
| .jccfg3 | FlashGet Incomplete Download |
| .jcd | FlashGet Saved |
| .jcf | JAWS Configuration |
| .jclic | JClic Project Format |
| .jcm | Java Commerce Message |
| .jcp | Jesusonic Preset Format |
| .jcrypt | JCRYPT Encrypted Format |
| .jcs | Java Control Source |
| .jcsk | JetCast Skin |
| .jct | JCT |
| .jcz | Microsoft Liquid Motion Animation Format |
| .jdb | Norton Antivirus Definiton Update File Format |
| .jdc | JDownloader Links Format |
| .jdf | Adobe Acrobat Job Definition Format |
| .jdp | BlackBerry JDE |
| .jdw | BlackBerry JDE |
| .jdx | JSpell Dictionary |
| .jeb | PENSIM Output |
| .jed | Xilinx Integrated Software Environment Device Configuration Information Format |
| .jef | Janome Embroidery Layout Format |
| .jetinc | Eclipse IDE Template Fragment |
| .jewelquestsavedgame | Jewel Quest Saved Game |
| .jfd | JAWS Synopsis |
| .jff | JAWS Ini |
| .jffs2 | Journalling Flash File System 2 Disk Image |
| .jfi | JPEG File Interchange Format |
| .jfif | JPEG Interchange Format |
| .jfl | SigmaPlot |
| .jfr | WJVN Fragment |
| .jfs | Linux/Unix Journaling System |
| .jfx | J2 Fax |
| .jg4 | BigJig Jigsaw Puzzle Format |
| .jgcscs | EditPad Syntax Scheme |
| .jgd | Corel PaintShop Photo Pro Gradients |
| .jgf | JAWS Ini |
| .jgp | QWS3270 PLUS Session Parameter |
| .jgs | QWS3270 PLUS Script |
| .jgw | JPEG World Format |
| .jgz | Gzipped JavaScript Format |
| .jhm | Java Help Mapping |
| .jhtml | ATG Dynamo Server Page (Java HTML) |
| .jia | Digital Photo Navigator Album |
| .jic | Java Icon Format |
| .jif | JPEG Interchange Format |
| .jiff | JPG Bitmap Image |
| .jig | GameHouse Puzzle Jigsaw Game |
| .jigsaw | Jigsaw Explorer Puzzle Format |
| .jigz | Jiggsaw Puzzle |
| .jis | Japanese Industry Standard Text Format |
| .jisp | Tkabber Emoticon Set |
| .jit | Aika Online Texture |
| .jj | Doodle C64 Compressed Image Format |
| .jjf | Flash Jester Jugglor |
| .jjjs | Claris Organizer Format |
| .jkb | Quake 3 Arena Bot AI |
| .jkl | Jedi Knight |
| .jkm | JAWS Ini Configuration Format |
| .jks | Jedi Knight Save |
| .jl | Julia Source Code Format |
| .jlb | PAC Mate BX Keyboard Driver |
| .jlc | Byte Compiled Lisp-based Script |
| .jls | JAWS |
| .jma | NSRT Compressed Game |
| .jmd | Corel PaintShop Pro Image Map Settings |
| .jmf | Java Media Framework |
| .jml | Java Modeling Language Specification |
| .jmp | SAS JMP Discovery Chart-to-statistics |
| .jms | Voxtron TeleButler Interactive Voice Response Call Flow |
| .jmv | Jnes Record Format |
| .jmx | Apache JMeter |
| .jnb | SigmaPlot Workbook |
| .jng | JPEG Network Graphic Format |
| .jnilib | Mac OS X Java JNI Library Format |
| .jnl | Ingres Journal |
| .jnlp | Java Network Launching Protocol Format |
| .jnt | Microsoft Windows Journal Note Format |
| .jnx | Garmin Raster Map |
| .jo | Jo Audio Format |
| .jo-7z | Jo Audio Format |
| .job | Microsoft Windows Task Scheduler Task Object Format |
| .joboptions | Adobe Acrobat Job Options Format |
| .jobs | VirtualDub Job |
| .jod | Microsoft Jet OLEDB.4.0 |
| .joe | .joe Editor Document Format |
| .joined | HJSplit Data Format |
| .joml | JOOB Object Modelling Language |
| .jomproj | Microsoft Visual Studio JOOB Object Model Project |
| .jor | Microsoft SQL Server Journal |
| .jot | Jot+ Notes Note Data |
| .journal.doc | SolidWorks Design Journal Template |
| .journal_info_block | Apple Mac OS Xsystem |
| .joy | CryENGINE Facial Editor Joystick Settings Format |
| .jp1 | Japanese (Romaji) Text Format |
| .jp2 | JPEG 2000 Image Format (ISO 15444-1) Format |
| .jp3 | Electric Quilt |
| .jp4 | Electric Quilt |
| .jp5 | Electric Quilt |
| .jpa | Joomla Installation Backup |
| .jpage | Eclipse Java Scrapbook Page |
| .jpb | Publish Manager Report |
| .jpc | JPEG2000 Code Stream Image Format |
| .jpd | Joint PhotoDefiner Image Format |
| .jpe | JPEG Bitmap Image Format |
| .jpeg | JPEG Bitmap Image Format |
| .jpegenx | Egis Encrypted JPEG |
| .jpeg_160x120 | 160 X 120 Pixels JPEG Image |
| .jpeg_170x220 | 170 X 220 Pixels JPEG Image |
| .jpf | JPEG 2000 Extended Image Format (ISO 15444-2) Format |
| .jpg | JPEG Bitmap Image Format |
| .jpg2 | JPEG 2000 Image Format (ISO 15444-1) Format |
| .jpgenx | Egis Encrypted JPG |
| .jpgw | JPEG World Format |
| .jpgx | Egis Encrypted JPG Bitmap Image |
| .jpg_108x192 | Android Picture |
| .jpg_128x128 | Android Picture |
| .jpg_128x160 | Android Picture |
| .jpg_128x96 | Android Picture |
| .jpg_160x120 | Android Picture |
| .jpg_160x128 | Android Picture |
| .jpg_170x128 | Android Picture |
| .jpg_170x220 | Android Picture |
| .jpg_220x176 | Android Picture |
| .jpg_240x320 | Android Picture |
| .jpg_320x240 | Android Picture |
| .jpg_320x320 | Android Picture |
| .jpg_480x320 | Android Picture |
| .jpg_512x512 | Android Picture |
| .jpg_56x42 | Android Picture |
| .jpg_t | JPEG Image |
| .jph | JProbe Memory Snapshot Format |
| .jpi | Jupiter Encrypted XML |
| .jpl | JProbe Settings |
| .jpm | JPEG 2000 Multi-layer Image Format (ISO 15444-6) |
| .jpn | Windows Japanese Noise-Word List Format |
| .jpp | Jigsaw Puzzle Player Puzzle Definition |
| .jpr | Oracle JDeveloper Model Project |
| .jps | Stereospic JPEG Format |
| .jpt | Jprobe Threadalyzer Memory Snapshot |
| .jpw | ESRI JPEG World Format |
| .jpx | JPEG 2000 Extended Image Format (ISO 15444-2) Format |
| .jpz | Puzzle Solver Puzzle |
| .JQ3SaveGame | Jewel Quest III Saved Game |
| .jqx | Microsoft Windows Help Related |
| .jrc | PCjr Cartridge ROM Format |
| .jrf | The Jumbot Bot Level Navigation |
| .jrl | BioWare Aurora Game Engine Journal |
| .jrprint | JasperReports Print Format |
| .jrs | Extensible Storage Engine (ESE) Reserve Transaction Log Format |
| .jrtf | JAmes OS Rich Text Format |
| .jrxml | JasperReports Layout Format |
| .jrz | Sony Playstation Portable Game Data Format |
| .js | JavaScript Format |
| .jsa | JRun Server Application |
| .jsb | JAWS Script Binary |
| .jsc | JavaScript Config |
| .jsd | Jazer Financial Format |
| .jsda | Jazer Financial Format |
| .jse | JScript Encoded Script Format |
| .jsf | Adobe Fireworks Batch Script |
| .jsfl | Flash JavaScript Format |
| .jsh | JAWS Script Header Format |
| .jsi | JAWS Personalized Settings |
| .jsk | JetAudio |
| .jsl | Corel PaintShop Photo Pro Shapes |
| .jsm | JAWS Script Message |
| .jsml | JSim Model |
| .jsn | Shield Now Shield |
| .jso | Compressed ISO Image |
| .json | JavaScript Object Notation Format |
| .jsonp | JSON-with-padding Source Code |
| .jsp | JAVA Server Page Format |
| .jspa | Java Servlet Alias Format |
| .jspf | Java JSP Fragment |
| .jspx | XML Java Server Page |
| .jsr | Job Safety Report Definition |
| .jss | JAWS Script Source Format |
| .jst | Java Server Page |
| .jsv | Java Structure Viewer |
| .jsx | Adobe After Effects Script Format |
| .jsxbin | Binary JavaScript Format |
| .jsxinc | ExtendScript Included Script Format |
| .jt | JT Open CAD Format |
| .jtb | JTB JavaCC Grammar |
| .jtbackup | Just Type Notes Backup Format |
| .jtd | Ichitaro Document |
| .jtdc | Ichitaro Compressed Document |
| .jtf | JPEG Tagged Interchange Format Image |
| .jtg | Joint Test Action Group Configuration |
| .jtk | Sun Microsystems Java Toolkit |
| .jtl | JMeter Test Results |
| .jtp | Microsoft Windows Journal Template Format |
| .jtpl | Rational Application Developer WebContent Theme Template |
| .jts | JVC Cyberlink AVCHD Video Format |
| .jtt | Ichitaro Document Template |
| .jtv | JRiver Media Center Recorded TV Format |
| .jtx | Jrju Text Format |
| .jude | JUDE Project Format |
| .jvs | Web Proxy Autodiscovery Protocol Format |
| .jvsg | Video Surveillance Project |
| .jvt | JRiver Recorded Video |
| .jw | Microsoft WordPad |
| .jwc | JewelCase Maker Saved |
| .jwg | Java |
| .jwl | Roxio Jewel Case Format |
| .jwr | LegaSuite GUI J Walk Runtime |
| .jws | Oracle WebLogic Server Java Web Services Format |
| .jxr | JPEG XR Image |
| .jz | JamesZhu Internet Browser Database |
File extensions are not normally displayed to users. To change this, go to Control Panel, select Appearance and Personalization and Folder Options. Next, select the View and find the option "Hide extensions for known file types". The option should be deselected (cleared) and confirmed with OK.
