.J File Extension
File Type 1Java Source File
What is a J file?
Java source files most often have a .JAVA extension.
File Type 2JAR Archive
.J File Association 2
Compressed file archive created with JAR, the successor to the ARJ file compression program (which created .ARJ files); JAR is available in a 16-bit DOS version and a 32-bit Windows version.
Not related to the .JAR format, which is a Java Archive.
File Type 3JPEG Image
.J File Association 3
Compressed graphic that uses .JPEG image compression; may contain thousands of colors, which makes it a good format for storing digital photos; can use different levels of compression, but the more compression is used, the lower the quality of the resulting image.
Most JPEG files have a .JPG extension.