Notes: For simplicity, the Java^TM programming language is simply called "Java" in the rest of this document.
 

abstract class

A class that contains one or more abstract methods, and therefore can never be instantiated. Abstract classes are defined so that other classes can extend them and make them concrete by implementing the abstract methods.
 

abstract method

A method that has no implementation.
 

access control list

An authorization mechanism in a protocol that maintains lists of hosts that are allowed to access each server controlling a display. The access control list for a user or group in a particular realm specifies the privileges that the user or group is granted to access server resources. Resources include such things as files, directories, and servlets.
 

ACL

See access control list.
 

actual parameter list

The arguments specified in a particular method call. See also formal parameter list.
 

Administrators Group

On the Windows NT operating system, members of the Administrators Group have full access rights to system resources. This allows them to perform both critical and routine system maintenance. By default, the Windows NT operating system installs with a single user in the Administrators Group, with the username Administrator. This is roughly equivalent to the concept of superuser (root) implemented on UNIX platforms.
 

API

See Application Programming Interface.
 

applet

A program written in Java to run within a Java-compatible web browser, such as HotJava or Netscape Navigator.
 

Application Programming Interface (API)

The specification of how a programmer writing an application accesses the behavior and state of classes and objects.
 

argument

A data item specified in a method call. An argument can be a literal value, a variable, or an expression.
 

array

A collection of data items, all of the same type, in which each item's position is uniquely designated by an integer.
 

authentication

A security measure that allows servers and clients to verify their identity. See also certificate and certificate authority.

Bean

A reusable software component. Beans can be combined to create an application. Bean files will have the extension .jar or .ser.
 

binary operator

An operator that has two arguments.
 

bit

The smallest unit of information in a computer, with a value of either 0 or 1.
 

bitwise operator

An operator that manipulates two values comparing each bit of one value to the corresponding bit of the other value.
 

block

In Java, any code between matching braces. Example: { x = 1; }.
 

boolean

Refers to an expression or variable that can have only a true or false value. Java provides the boolean type and the literal values true and false.
 

byte

A sequence of eight bits. Java provides a corresponding byte type.
 

bytecode

Machine-independent code generated by the Java compiler and executed by the Java interpreter.
 

cache

A storage area that contains copies of original data stored locally so that the data doesn't have to be retrieved from a remote server each time it is requested.
 

caching

Caching allows copies of retrieved objects to be stored in the file system or memory of the proxy service. These copies are then used to satisfy subsequent requests for the same URL. This reduces delay in the delivery of documents to the client, saves network bandwidth, and eliminates the need for a large browser cache.
 

casting

Explicit conversion from one data type to another.
 

certificate

Sometimes referred to as a digital certificate. This is a digital document containing identifying information about a user or web site. Certificate information typically contains the username, signing certificate authority, and the validity period.
 

certificate authority

Entities that issue the digitally signed certificates containing information used to identify the user or site. When you accept a certificate signed by a given certificate authority, you are saying you trust that authority to have verified the identify of the person or site.
 

CGI

See Common Gateway Interface.
 

class

In Java, a type that defines the implementation of a particular kind of object. A class definition defines instance and class variables and methods, as well as specifying the interfaces the class implements and the immediate superclass of the class. If the superclass is not explicitly specified, the superclass will implicitly be Object.
 

class method

A method that is invoked without reference to a particular object. Class methods affect the class as a whole, not a particular instance of the class. Also called a static method. See also instance method.
 

classpath

A classpath is an environmental variable which tells the Java Virtual Machine and other Java applications (for example, the Java tools located in the JDK1.1.X\bin directory) where to find the class libraries, including user-defined class libraries.
 

class variable

A data item associated with a particular class as a whole--not with particular instances of the class. Class variables are defined in class definitions. Also called a static field. See also instance variable
 

comment

In a program, explanatory text that is ignored by the compiler. In Java programs, comments are delimited using // or /*...*/.
 

Common Gateway Interface (CGI)

A standard for how external applications interface with information servers. It defines how executable scripts are called and how data is passed between the server and the script. Information on CGI can be found on the National Center for Supercomputing Applications (NCSA) HTTPd website at: http://hoohoo.ncsa.uiuc.edu/
 

compiler

A program to translate source code into code to be executed by a computer. The Java compiler translates Java source code into Java bytecode. See also interpreter.
 

constructor

A pseudo-method that creates an object. In Java, constructors are instance methods with the same name as their class. Java constructors are invoked using the new keyword.
 

content server

A server that contains the original documents that are requested by clients directly or through a proxy server.
 

cookie

The most common meaning of "cookie" on the Internet refers to a piece of information sent by a web server to a web browser that the browser software is expected to save and to send back to the server whenever the browser makes additional requests from the server.
 

core class

A public class (or interface) that is a standard member of the Java Platform. The intent is that the Java core classes, at minimum, are available on all operating systems where the Java Platform runs. A 100%-pure Java program relies only on core classes, meaning it can run anywhere. All core classes reside in the java.* package.
 

critical section

A segment of code in which a thread uses resources (such as certain instance variables) that can be used by other threads, but that must not be used by them at the same time.
 

declaration

A statement that establishes an identifier and associates attributes with it, without necessarily reserving its storage (for data) or providing the implementation (for methods). See also definition.
 

definition

A declaration that reserves storage (for data) or provides implementation (for methods). See also declaration.
 

DELETE

A security permission granted in the access control list that allows users or groups to delete data from server.  

deprecation

Refers to a class or method that is no longer important, and will probably cease to exist in the future.
 

derived from

Class X is "derived from" class Y if class X extends class Y. See also subclass, superclass.
 

distributed

Running in more than one address space.
 

encryption

The process of protecting information from unauthorized use by making the information indecipherable. Encryption is based on a code, known as a key, which is used to decrypt the information.
 

extends

Class X extends class Y to add functionality, either by adding fields or methods to class Y, or by overriding methods of class Y. An interface extends another interface by adding methods. Class X is said to be a subclass of class Y. See also derived from.
 

field

A data member of a class. Unless specified otherwise, a field is not static.
 

FAQ

See Frequently Asked Questions.
 

File Transfer Protocol (FTP)

The basic Internet file transfer standard. File Transfer Protocol, which is based on TCP/IP, enables the fetching and storing of files between hosts on the Internet. See also TCP/IP.
 

filter

A filter servlet is simply a servlet that performs some filtering task. A filter rule is a trigger that enables a filter servlet.
 

firewall

A network configuration, usually both hardware and software, that forms a fortress between networked computers within an organization and those outside the organization. It is commonly used to protect information such as a network's e-mail and data files within a physical building or organization site.
 

formal parameter list

The parameters specified in the definition of a particular method. See also actual parameter list.
 

Frequently Asked Questions

Frequently Asked Questions are documents that list and answer the most common questions on a particular subject.
 

FTP

See File Transfer Protocol.
 

garbage collection

The automatic detection and freeing of memory that is no longer in use. The Java runtime system performs garbage collection so that programmers never explicitly free objects.
 

GET

A security permission granted in the access control list that allows users or groups to retrieve information from the server.  

GUI

Graphical User Interface. Refers to the techniques involved in using graphics, along with a keyboard and a mouse, to provide an easy-to-use interface to some program.
 

header

In Internet terms, part of an HTTP request or response that carries information about the request, the response or its content.
 

heap

The area in memory available for read/write.
 

hierarchy

A classification of relationships in which each item except the top one (known as the root) is a specialized form of the item above it. Each item can have one or more items below it in the hierarchy. In the Java class hierarchy, the root is the Object class.
 

HotJava Browser

An easily customizable web browser developed by Sun Microsystems, which is written in Java.
 

HTML

See HyperText Markup Language.
 

HTTP

See Hypertext Transfer Protocol.
 

HTTPD

See Hypertext Transfer Protocol Daemon.
 

HTTPS

See Secure Hypertext Transfer Protocol.
 

HyperText Markup Language (HTML)

This is a file format, based on SGML, for hypertext documents on the Internet. It is very simple and allows for the embedding of images, sounds, video streams, form fields and simple text formatting. References to other objects are embedded using URLs.
 

Hypertext Transfer Protocol (HTTP)

The Internet protocol, based on TCP/IP, used to fetch hypertext objects from remote hosts. See also TCP/IP.
 

Hypertext Transfer Protocol Daemon (HTTPD)

HTTP daemon, a program that serves information using the HTTP protocol.
 

identifier

The name of an item in a Java program.
 

inheritance

The concept of classes automatically containing the variables and methods defined in their supertypes. See also superclass, subclass.
 

instance

An object of a particular class. In Java programs, an instance of a class is created using the new operator followed by the class name.
 

instance method

Any method that is invoked with respect to an instance of a class. Also called simply a method. See also class method.
 

instance variable

Any item of data that's associated with a particular object. Each instance of a class has its own copy of the instance variables defined in the class. Also called a field. See also class variable.
 

interface

In Java, a group of methods that can be implemented by several classes, regardless of where the classes are in the class hierarchy.
 

Internet

An enormous network consisting of literally millions of hosts from many organizations and countries around the world. It is physically put together from many smaller networks and data travels by a common set of protocols.
 

internationalization

When an application is designed so that it can be adapted to many languages and regions without recompiling. The textual data (such as messages and GUI component labels) and other culturally dependant data (such as dates and currencies) are isolated from the rest of the application in a set of files, one set containing the text for a given language and region.
 

Internet Cache Protocol (ICP)

A message format for communicating between Web caches. Typically used to locate objects in neighboring caches. The caches can be connected in any non-cyclical pattern including hierarchical.
 

Internet Protocol (IP)

The basic protocol of the Internet. It enables the unreliable delivery of individual packets from one host to another. It makes no guarantees about whether the packet will be delivered, how long it will take, or if multiple packets will arrive in the order they were sent. Protocols built on top of this add the notions of connection and reliability. See also TCP/IP.
 

interpreter

A module that alternately decodes and executes every statement in some body of code. The Java interpreter decodes and executes Java bytecode. See also compiler, runtime system.
 

IP

See Internet Protocol.
 

JAR Files (.jar)

Java ARchive. A file format used for aggregating many files into one.
 

JAR file format

JAR (Java Archive) is a platform-independent file format that aggregates many files into one. Multiple Java applets and their requisite components (.class files, images, sounds and other resource files) can be bundled in a JAR file and subsequently downloaded to a browser in a single HTTP transaction. It also supports file compression and digital signature
 

Java

An object-oriented programming language developed by Sun Microsystems. A "write once, run anywhere" programming language.
 

Java Application Environment

The source code release of the Java Development Kit.
 

JavaBeans

A portable, platform-independent reusable component model.
 

Java Blend

A product that enables developers to simplify database application development by mapping database records to Java objects and Java objects to databases.
 

Java Developer Connection (JDC)

A service designed for individual developers, providing online training, product discounts, feature articles, bug information, and early access capabilities.
 

Java Database Connectivity (JDBC)

An industry standard for database-independent connectivity between Java and a wide range of databases. The JDBC provides a call-level API for SQL-based database access.
 

Java Development Kit (JDK)

A software development environment for writing applets and application in Java.
 

Java Interface Definition Language (JIDL)

Java APIs that provide standards-based interoperability and connectivity with CORBA (Common Object Request Broker Architecture).
 

Java Platform

The Java Virtual Machine and the Java core classes make up the Java Platform. The Java Platform provides a uniform programming interface to a 100% Pure Java program regardless of the underlying operating system.
 

Java Remote Method Invocation (RMI)

A distributed object model for Java-to-Java applications, in which the methods of remote Java objects can be invoked from other Java virtual machines, possibly on different hosts.
 

Java Runtime Environment (JRE)

A subset of the Java Developer Kit for end-users and developers who want to redistribute the JRE. The JRE consists of the Java Virtual Machine, the Java Core Classes, and supporting files.
 

Java Virtual Machine (JVM)

The part of the Java Runtime Environment responsible for interpreting Java bytecodes.
 

JavaScript

An open, cross-platform object language developed by Netscape for creating and customizing applications. Commonly confused with Java.
 

Java Software Division (previously JavaSoft)

A business unit of Sun Microsystems, Inc.
 

JDBC

See Java Database Connectivity.
 

JDC

See Java Developer Connection.
 

JDK

See Java Development Kit.
 

JIDL

See Java Interface Definition Language.
 

JRE

See Java Runtime Environment.
 

JRMI

See Java Remote Method Invocation.
 

JVM

See Java Virtual Machine.
 

local variable

A data item known within a block, but inaccessible to code outside the block. For example, any variable defined within an Java method is a local variable and can't be used outside the method.
 

member

A field or method of a class. Unless specified otherwise, a member is not static.
 

method

A function defined in a class. See also instance method, class method. Unless specified otherwise, a method is not static.
 

MIME

See Multi-Purpose Internet Mail Extensions.
 

Multi-Purpose Internet Mail Extensions (MIME)

An emerging standard for multimedia e-mail and messaging.
 

multithreaded

Describes a program that is designed to have parts of its code execute concurrently. See also thread.
 

National Center for Supercomputer Applications (NCSA)

National Center for Supercomputer Applications.
 

NCSA

See National Center for Supercomputer Applications.
 

object

The principal building blocks of object-oriented programs. Each object is a programming unit consisting of data (instance variables) and functionality (instance methods). See also class.
 

object-oriented design

A software design method that models the characteristics of abstract or real objects using classes and objects.
 

overloading

Using one identifier to refer to multiple items in the same scope. In Java, you can overload methods but not variables or operators.
 

overriding

Providing a different implementation of a method in a subclass of the class that originally defined the method.
 

package

A group of types. Packages are declared with the package keyword.
 

POST

A security permission granted in the access control list that allows users or groups to put new data on the server.  

process

A virtual address space containing one or more threads.
 

proxy

Server software, typically installed on the firewall, that allows access to the Internet across the firewall. A proxy is a special server that typically runs in conjunction with firewall software. The proxy server waits for a request from inside the firewall, forwards the request to the remote server outside the firewall, reads the response, then sends the response back to the client.
 

proxy chaining

Setting up a proxy so that it performs its requests through another proxy server (or service).
 

Public Key Certificate

A security measure that authenticates the server to its clients and to the external server, so that they can tell who you "really" are. See also certificate and certificate authority.  

PUT

A security permission granted in the access control list that allows users or groups to put a new copy of existing data on the server.  

RAM

See Random Access Memory.
 

Random Access Memory

Volatile memory, which can be written as well as read. More specifically, it is semiconductor-based memory that can be read or written by the CPU or other hardware devices. The storage locations can be accessed in any order.
 

realm

A database of users, groups, and access control lists. Used to specify which users have access to the resources of a specific service (for example, to the Web Page Service).
 

redirection

A system by which clients accessing a particular URL are sent to a different location, either on the same server or on a different server. This is useful if a resource has moved and you want the clients to use the new location transparently. It is also used to maintain the integrity of relative links when directories are accessed without a trailing slash.
 

reference

A data element whose value is an address.
 

regular expression

A form of expression that is used in proxy for wildcard patterns for access control.
 

Remote Procedure Call (RPC)

Executing what looks like a normal procedure call (or method invocation) by sending network packets to some remote host.
 

request

A message from a client to a server which asks for a piece of information.
 

response

A reply from a server to a client.
 

resource

Any document (URL), directory, or program that the server can access and send to a client.
 

RMI

See Remote Method Invocation.
 

root

On UNIX operating systems, the name of the superuser (root). The special username root carries with it permissions to access any file and carry out other operations not permitted to ordinary users. Roughly equivalent to the Administrator username on Windows NT operating systems. See Administrators Group.
 

RPC

See Remote Procedure Call.
 

runtime system

The software environment in which programs compiled for the Java Virtual Machine can run. The runtime system includes all the code necessary to load Java programs, dynamically link native methods, manage memory, handle exceptions, and an implementation of the Java virtual machine, which may be a Java interpreter.
 

scope

A characteristic of an identifier that determines where the identifier can be used. Most identifiers in Java have either class or local scope. Instance and class variables and methods have class scope; they can be used outside the class and its subclasses only by prefixing them with an instance of the class or (for class variables and methods) with the class name. All other variables are declared within methods and have local scope; they can be used only within the enclosing block.
 

Secure Hypertext Transfer Protocol (HTTPS)

A protocol, built on top of SSL, that is a secure version of HTTP. See also Hypertext Transfer Protocol and Secure Sockets Layer.
 

Secure Sockets Layer

A protocol that allows communication between a Web browser and a server to be encrypted for privacy.
 

server

A server is a process. One server can support a variety of different services at the same time.
 

service

Services are implementations of individual application-level protocols, such as HTTP, FTP, or DHCP.
 

servlet

A servlet is a Java-based extension mechanism for many common services, and in particular, for HTTP.
 

session

A session is a series of requests from a given user (browser and machine) that occurs during a continuous time-period. This transaction model for sessions has many benefits over the single-hit model. For instance, it can maintain state (data) and user identity across multiple page requests in an e-commerce application.
 

SSL

See Secure Sockets Layer.
 

subclass

A class that is derived from a particular class, perhaps with one or more classes in between. See also superclass.
 

superclass

A class from which a particular class is derived, perhaps with one or more classes in between. See also subclass.
 

superuser

On a UNIX system, refers to the person logged in under the special username root. The superuser has higher access privileges than regular users. This allows the superuser to carry out essential system maintenance that, for security reasons, regular users are not allowed to perform.
 

TCP/IP

See Transmission Control Protocol.
 

thread

The basic unit of program execution. A process can have several threads running concurrently, each performing a different job, such as waiting for events or performing a time-consuming job that the program doesn't need to complete before going on. When a thread has finished its job, the thread is suspended or destroyed. See also process.
 

timeout

A specified time after which the server should give up trying to finish a service routine that appears hung.
 

Transmission Control Protocol (TCP/IP)

Internet protocol that provides for the reliable delivery of streams of data from one host to another. Based on IP.
 

type

A class or interface.
 

URL

Uniform Resource Locator. A standard for writing a text reference to an arbitrary piece of data in the WWW. A URL looks like "protocol://host/localinfo" where protocol specifies a protocol to use to fetch the object (like HTTP or FTP), host specifies the Internet name of the host on which to find it, and localinfo is a string (often a file name) passed to the protocol handler on the remote host.
 

variable

An item of data named by an identifier. Each variable has a type, such as int or Object, and a scope. See also class variable, instance variable, local variable.
 

virtual machine

An abstract specification for a computing device that can be implemented in different ways, in software or hardware. You compile to the instruction set of a virtual machine much like you'd compile to the instruction set of a microprocessor. The Java Virtual Machine consists of a bytecode instruction set, a set of registers, a stack, a garbage-collected heap, and an area for storing methods.
 

WWW

World Wide Web. The web of systems and the data in them that is the Internet. See also Internet.
 

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