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PC And Internet Glossary - Including File Extensions - J

JA

File extension. See this entry on my Trainz Wordz page.

JAR

File extension. Java archive. JAR files have a very similar (possibly identical) format to PKZIP/WinZip ZIP archive files, but contain Java class files. Many similar files have an extension of ZIP, although ZIP archive files can contain any type of file. Normally, the contents of JAR files or ZIP files containing Java class files do not have to be extracted before they can be used. JAR files can contain viruses, but in theory the virtual machine which runs Java programs should prevent any malicious actions.

Java

  1. A programming language used on some web pages. Java programs are automatically run by most modern web browsers. Older web browsers may not run Java at all or may suffer from frequent problems due to not supporting recently introduced aspects of the language. JavaScript is a completely separate and very different programming language.

  2. File extension. A Java program source file.

Java VM

Java Virtual Machine. See Virtual Machine.

Java Web Start

A program (javaws.exe) which reads *.JNLP files and obeys their instructions, so as to download, install and/or run Java programs as standalone programs which do not run in a web browser.

It would appear that, based on the instructions in the relevant JNLP file, Java Web Start will automatically download a Java program if it has not previously been downloaded, otherwise it will run the downloaded copy. It will also automatically check for the availability of a later version of the program and download that, replacing the old version. Java Web Start performs these tasks in the background and in combination with a web browser program. However, the actual Java program does not run in a web browser, which is somewhat confusing.

Java Web Start is installed by the Java-enabled version of Netscape V7.1, and probably by modern Java-enabled versions of other non-Microsoft web browser programs such as Mozilla and Opera.

The situation regarding Java Web Start and Internet Explorer is vague and liable to change due to litigation between Microsoft and Sun.

There is more information about Java Web Start in "C:\Program Files\Java Web Start\Readme.html" (provided Java Web Start has been installed) and also online at "http://www.mindprod.com/jgloss/jgloss.html".

Java Web Start is a bizarre, non-standard and highly complicated system for installing and running programs, which most Windows users will not be familiar with.

JavaScript

A programming language used on some web pages. JavaScript programs are automatically run by most modern web browsers. JavaScript is very different to Java and is a very much simpler language to learn. Older web browsers may not run JavaScript at all or may suffer from frequent problems due to not supporting recently introduced aspects of the language. JScript is Microsoft's dialect of JavaScript.

JAVASUP

Sometimes spuriously listed as having failed to load in Bootlog.txt. See Microsoft KnowledgeBase article 127970 for details of the various misleading spurious error messages which can appear in Bootlog.txt.

JDK

Java Development Kit. I think this means a program in which you can write and compile Java programs. The term SDK for Java (Software Development Kit for Java) probably has the same meaning.

JET

"Jet". The database engine used in Microsoft Access. I don't know if the letters mean anything. According to a Microsoft document, Jet will be installed on a computer if you install Access, Visual BASIC, or Microsoft Office. I don't know whether Jet is always installed with Office or whether this depends on which Office components are selected.

JIT

Just In Time. A type of compiler/interpreter. Commands are compiled into machine code just before being obeyed. Said to run programs faster than a normal interpreter. Sometimes used with languages such as Java. Referred to by cynics as FTL - Far Too Late. The JIT option for the Java Virtual Machine in Internet Explorer does run many Java applets significantly faster but a small number of applets fail to run at all when the option is enabled.

JNLP

File extension. Java Network Launching Protocol. XML plain text data files, read by the Java Web Start program. Double-clicking a JNLP file causes it to be opened with Java Web Start, assuming that Java Web Start has been installed.

Join

In modern database systems, a join is a connection between two tables (see "Table"). Without a join between two tables, some database programs will return all combinations of records in the two tables, in other words each of the records in the first table matched with each of the records in the second table. This is not normally useful. A join, usually between two identically named fields, will restrict the result to those combinations of records in which the value of the relevant field is the same in both tables, which is usually what is required. The join effectively performs a lookup from one table to the other. This description of joins is simplistic - in practice the database system may allow inner joins, outer joins, self-joins, one-to-one joins, one-to-many joins, many-to-one joins and many-to-many joins. A join is very similar to a relationship between the tables.

Joliet

One of several possible file systems which can used on CD's. Joliet allows a maximum filename length of 64 characters (although I do not know if this includes the final full stop and the extension or not). This is more restrictive than Windows 9x. It allows use of Unicode characters and spaces. In particular it certainly allows the following characters:
abcdefghijklmnopqrstuvwxzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 _:-',()
It may also allow some additional characters. Multiple full stops are permitted, for example R.E.M. - Find The River.mp3 is a legal Joliet filename. However, semi-colons are NOT permitted (actually, they should in theory be treated as a separator between the extension and a file version number). Joliet CD's can be read by MS-DOS, Windows 9x, Windows NT, recent versions of Linux, older versions of Linux (this requires a patch) and OS/2 (this also requires a patch). See also ISO9660.

Joomla

A CMS (Content Management System).

Journalling

See Outlook.

JPG

"Jay - peg". File extension. Joint Photographic Experts Group. Also sometimes called JPEG. A type of very highly compressed graphic image file extremely widely used on the Internet. Ideal for photographs but unsuitable for images having large areas with identical colours (for which GIF is much preferable). JPG is lossy but the distortion can easily be made undetectable to the eye. JPG should only be used for the final published version of a photograph, not for editing, since the distortions build up. I believe that the JPG algorithm uses fractal mathematics to achieve the compression.

JRE

Java Runtime Environment. Same as a Java Virtual Machine (see that entry).

JS

File extension. JavaScript program. JS files can contain viruses. In theory the mechanism which runs JavaScript programs should prevent any malicious actions. However, in Microsoft programs this safety mechanism may not be fully secure.

JSE

File extension. JavaScript Encoded Script file. JSE files can contain instructions which could perform undesirable operations on a computer.

JScript

Microsoft's dialect of the JavaScript programming language. I do not know how much it differs from the standard.

JSP

File extension. A web page HTML file which includes a reference to a Java applet which acts as a server. I do not know whether JSP files can contain viruses or not.

Jumper

A tiny plastic square shaped device containing a metal contact, which can be pulled on and off two pins on a printed circuit board, so as to connect them together or not as desired. Jumpers can be used to set a device's configuration. DIP switches an alternative method of achieving the same result. As configuration is increasingly done by software instead of hardware, DIP switches and jumpers are far fewer in number these days. See also Open and Closed.

JVM

Java Virtual Machine. Software (in effect, an emulator) which allows Java programs to be run on a PC.
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