jack

n. A connector designed to receive a plug. A jack is commonly used in making audio and video connections.

jaggies

n. The "stairsteps" that appear in diagonal lines and curves drawn at low resolutions in computer graphics. Also called aliasing.

Java

n. An object-oriented programming language, developed by Sun Microsystems, Inc. Similar to C++, Java is smaller, more portable, and easier to use than C++ because it is more robust and it manages memory on its own. Java was also designed to be secure and platform-neutral (meaning that it can be run on any platform) through the fact that Java programs are compiled into bytecodes, which are similar to machine code and are not specific to any platform. This makes it a useful language for programming Web applications, since users access the Web from many types of computers. Currently, the most widespread use of Java is in programming small applications, or applets, for the World Wide Web. See also bytecode, Java applet, object-oriented programming.

Java applet

n. A Java class that is loaded and run by an already-running Java application such as a Web browser or an applet viewer. Java applets can be downloaded and run by any Web browser capable of interpreting Java, such as Internet Explorer, Netscape Navigator, and HotJava. Java applets are frequently used to add multimedia effects and interactivity to Web pages, such as background music, real-time video displays, animations, calculators, and interactive games. Applets can be activated automatically when a user views a page, or they may require some action on the part of the user, such as clicking on an icon in the Web page. See also applet, Java.

Java chip

n. An implementation on a single integrated circuit of the virtual machine specified for execution of the Java programming language. Such chips, which are being developed by Sun Microsystems, Inc., could be used in very small devices and as controllers for appliances. See also integrated circuit, Java, virtual machine.

Java-compliant browser

n. A Web browser with support for the Java programming language built into it. Most current Web browsers are Java-compliant. See also Java, Web browser.

Java Developer's Kit

n. A set of software tools developed by Sun Microsystems, Inc., for writing Java applets or applications. The kit, which is distributed free, includes a Java compiler, interpreter, debugger, viewer for applets, and documentation. See also applet, Java, Java applet. Acronym: JDK.

Java Management Application Programming Interface

n. A set of application programming interface specifications, proposed by Sun Microsystems, Inc., to enable the Java language to be used for network management. See also application programming interface, Java. Acronym: JMAPI.

JavaScript

n. A scripting language developed by Netscape Communications and Sun Microsystems, Inc. that is loosely related to Java. JavaScript, however, is not a true object-oriented language, and it is limited in performance compared with Java because it is not compiled. Basic online applications and functions can be added to Web pages with JavaScript, but the number and complexity of available application programming interface functions are fewer than those available with Java. JavaScript code, which is included in a Web page along with the HTML code, is generally considered easier to write than Java, especially for novice programmers. A JavaScript-compliant Web browser, such as Netscape Navigator, is necessary to run JavaScript code. See also application programming interface, HTML, scripting language. Compare Java.

Java terminal

n. A type of personal computer with a reduced number of components that is built primarily to provide an access terminal to the Web, including downloadable Java applets. Typically, such machines will not have locally addressable hard disks or installable programs, but will obtain any necessary materials, including Java applets, for the user from somewhere on the network. Centrally obtained software is generally less expensive to administer but usually requires some download delay before usage may begin. Java terminals, currently under development by Sun Microsystems, Inc., are similar in concept to NetPCs. See also Java, Java applet, network computer. Compare NetPC.

JCL

n. Acronym for Job Control Language. A command language used in IBM OS/360 mainframe systems. JCL is used to launch applications and specifies information on running time, program size, and the program files used for each application. See also command language.

JDK

n. See Java Developer's Kit.

jewel box

n. A clear plastic container used to package and store a compact disc. Also called jewel case.

job queue

n. A list of programs or tasks waiting for execution by a computer. Jobs in the queue are often ordered according to some basis of priority. See also queue.

Joliet

n. An extension to the ISO 9660 (1988) standard developed to include long filenames or filenames outside the 8.3 convention. This format is used in some new CD-ROMs for operating systems, such as Windows 95, that can handle such filenames. See also 8.3, ISO 9660, long filenames.

journal

n. A computer-based log or record of transactions that take place in a computer or across a network. A journal could be used, for example, to record message transfers on a communications network, to keep track of system activities that alter the contents of a database, or to maintain a record of files that have been archived for storage or deleted from the system. A journal is often kept as a means of reconstructing events or sets of data should they become lost or damaged. See also audit trail.

joystick

n. A pointing device used mainly but not exclusively for computer games. A joystick has a base, on which control buttons can be mounted, and a vertical stem, which the user can move in any direction to control the movement of an object on the screen; the stem may also have control buttons. The buttons activate various software features, generally producing on-screen events. A joystick is usually used as a relative pointing device, moving an object on the screen when the stem is moved and stopping the movement when the stem is released. In industrial control applications, the joystick can also be used as an absolute pointing device, with each position of the stem mapped to a specific location on the screen. See also absolute pointing device, relative pointing device.

JPEG

n. 1. Acronym for Joint Photographic Experts Group. An ISO/ITU standard for storing images in compressed form using a discrete cosine transform. JPEG trades off compression against loss; it can achieve a compression ratio of 100:1 with significant loss and possibly 20:1 with little noticeable loss. 2. A graphic stored as a file in the JPEG format.

JScript

n. Microsoft's version of JavaScript, which is built into the Microsoft Internet Explorer Web browser. JScript is a powerful scripting language targeted specifically for the Internet. It is implemented as a fast, portable, lightweight interpreter for use in World Wide Web browsers and other applications that use Microsoft ActiveX Controls, Automation servers, and Java applets. See also ActiveX controls, Java, JavaScript.

Julian calendar

n. The calendar introduced by Julius Caesar in 46 B.C. to replace the lunar calendar. The Julian calendar provided for a year of 365 days with a leap year every 4 years, or an average year length of 365.25 days. Because the solar year is slightly shorter, the Julian calendar gradually moved out of phase with the seasons and was superseded by the Gregorian calendar, introduced by Pope Gregory XIII. Compare Gregorian calendar.

Julian date

n. 1. A date expressed as the number of days elapsed since January 1, 4713 B.C. (on the Julian calendar)-- for example, 2,450,000 for October 9, 1995 (Gregorian). Julian dates are useful for finding elapsed times between events that may be many years apart, as in astronomy. The starting point is the beginning of the Julian Period, defined in 1583 by Joseph Scaliger as the coincidence of several cycles based on the Julian calendar. See also Gregorian calendar, Julian calendar. 2. Often (but incorrectly), a date expressed as the year and the number of days elapsed since the beginning of the year--for example, 91.13 for January 13, 1991. Acronym: JD.

jumper

n. A small plug or wire that can be connected between different points in an electronic circuit in order to alter an aspect of a hardware configuration. Compare DIP switch.

just-in-time