Notice: This material is excerpted from Special Edition Using Java, ISBN: 0-7897-0604-0. The electronic version of this material has not been through the final proof reading stage that the book goes through before being published in printed form. Some errors may exist here that are corrected before the book is published. This material is provided "as is" without any warranty of any kind.

Appendix E - Glossary

by Mary Pietrowicz

.class file A file containing machine-independent Java bytecodes. The Java compiler generates .class files for the Java interpreter to read.

.java file A file containing Java source code.

abstract class A class that is not instantiated directly. Abstract classes exist so that subclasses can inherit variables and methods from them.

access control A way to restrict access to a class's variables and methods. The modifiers public, private, protected, and private protected placed before a variable name or function declaration specify the kind of access granted.

action An applet method that can be defined to identify the kind of event that has occurred and act on that event.

API Application Programming Interface. The Java API contains classes a developer can use to build applications and applets. Currently, the Java API provides classes to support the language itself, I/O capability, network capability, user interfaces, applets, image management, interaction with a platform-specific toolkit, and general utilities.

applet A Java program that runs in the context of a Java-capable browser or the appletviewer. Java applets extend the content of Web pages beyond just graphics and text.

appletviewer A tool created by SUN to run applets without a browser.

array An indexed set of data, where each data item is of the same type. An element of an array is referenced by its index.

attribute A specifier for an HTML tag (for example, code is an attribute of the <APPLET> tag).

attributes An object's variables, or state information.

AWT The Abstract Windowing Toolkit, or group of classes for writing programs with graphical user interfaces. The AWT contains classes for Components (for example, Button, TextField, Canvas, Choice, List, TextArea, Checkbox, List, MenuItem, Scrollbar, Label), classes for Containers (for example, Window, Frame, Panel, Dialog, FileDialog), and classes to help with layout, graphics, and images.

behavior Describes the way a class reacts to events in the environment, messages, and changes to variables. Behavior depends on the state of an object. A class maintains state information in its variables and reacts to its environment through its methods.

browser A program used for reading, displaying, and interacting with objects on the World Wide Web.

bytecode The machine-independent output of the Java compiler and input to the Java interpreter.

cast To coerce an object of one data type to another type.

class A collection of variables and methods that an object can have, or a template for building objects.

CLASSPATH An environment variable used to define all the directories where .class files can be found.

class variable A variable allocated once per class. Class variables have global class scope and belong to the entire class instead of an instance.

code An attribute of the HTML <APPLET> tag that specifies the class to load. The term "code" also refers to source code, which is the syntactical representation of a program.

codebase An attribute of the HTML <APPLET> tag that specifies the location of the classes to load.

compiler A language translator. A program that transforms source code into another format without executing the program.

conditionals Programming constructs that support branching or execution of different statements when different conditions are true. Java conditionals are case statements, if statements, and the ? (conditional) operator.

constructor A method that is used to create an instantiation of a class.

content handler A Java routine used to process a particular MIME type (for example, text/html).

destroy() An applet method used to do final cleanup before an applet unloads. Applets override this method when resources need to be released that are not released by the stop() method.

double buffering A technique used to reduce flicker in animations. The image or drawing is painted into a temporary space. Then the finished object is drawn to the screen all at once.

DTD Abbreviation for Document Type Definition. A DTD file formally describes a particular markup language, such as HTML.

encapsulation A way to contain data and methods in a class so that its methods and variables may be added, changed, or deleted without requiring the code that uses the class to change. This object-oriented programming technique makes a class look like a black box to the outside world.

event handling Identifying events (for example, mouse clicks and button presses) and reacting to them. Events can be handled with the action method, a method corresponding to the event (for example, MouseDown), or the handleEvent method.

exception A signal that something has happened to stop normal execution of a program, usually an error.

exception handler Code that responds to and attempts to recover from an exception.

expression Mathematical, comparative and other kinds of operations that can be evaluated to a single value. For example, 1+3+9*7+Math.pow(45,3.3) is an expression.

extends A keyword used to make one class a subclass of another, for example, class subclass extends superclass.

final A modifier that prevents subclass definition, makes variables constant, and prevents a subclass from overriding a method.

finalize A method that is called when there are no further references to an object and it is no longer needed. This method releases resources and does any other necessary cleanup that Java does not handle during garbage collection.

Gamelan A registration site on the Web for Java applets and applications. Items registered here often contain the Java source.

garbage collection thread A Java thread that automatically frees memory that is no longer needed by objects.

GUI Graphical User Interface. In Java, the AWT provides classes to support user interface construction.

HotJava A Java-capable browser from Javasoft.

hspace An attribute of the HTML <APPLET> tag that specifies the amount of horizontal space (to the left and right) between the applet and the text on the page.

HTML Hypertext Markup Language, the language used to create Web pages.

inheritance A property of object-oriented languages where a class assumes the methods and variables of more general classes. A subclass automatically contains all of the methods and variables that its superclasses contain. Note that access modifiers such as private can place restrictions on the use of inherited items in Java.

init() An applet method used to do one-time initialization before an applet begins executing.

instance A concrete representation of a class or object. A class can have many instances.

instance variable A variable allocated once per instance of a class.

instantiate To create a concrete object from a class "template." New objects are instantiated with new.

interface A collection of methods and variables that other classes may implement. A class that implements an interface provides implementations for all of the methods in the interface.

interpreter A program that performs both language translation and program execution. java is the Java interpreter.

java The program used to invoke the Java interpreter, which executes Java programs.

Java An object-oriented language that can be used to create machine-independent applications and applets.

java.applet Java package that supports applet development. This package provides the ability for an applet to get information about its context, communicate with other applets, load images, and play sounds.

java.awt Java package that supports the development of user interfaces.

java.awt.image Java package that supports image processing.

java.awt.peer Java package that links Java user interface code with a platform-dependent toolkit like Motif or Windows.

java.io Java package that supports reading and writing of files, strings, sockets, and so on.

java.lang Java package that supports the basic features of the language. This class does not have to be explicitly imported into Java programs; it is imported automatically.

java.net Java package that supports network connections.

java.util Java package that provides useful utility classes like random number generation and growable arrays.

javac A command for running the Java compiler.

javac_g A command for running a non-optimized version of the Java compiler. The javac_g command can be used with debuggers, such as jdb.

Java-capable browser A Web browser that can run Java applets. Also called a Java-enabled or Java-enhanced browser.

javadoc A command that is used to generate API-style HTML documentation automatically.

javah A command that can create C include files and stubs from a Java .class file. The resulting C files allow C code to access parameters passed from Java, return values to Java, and access Java class variables.

javah_g A command that can create C include files and stubs with debug information from a Java .class file.

javap A command that disassembles Java .class files.

JavaScript A Java-based scripting language.

Java-SIG The Sun User Group's Special Interest Group for Java.

jdb The Java debugger.

JDBC A database access API from JavaSoft that allows developers to access databases with Java programs.

JDK The Java Developers Kit.

literals Numbers or character values. 'x', '2', and '1.22' are all literals.

loops Programming constructs that support repetitive execution of one or more statements. Java has while, do-while, and for loops.

main() The entry point into a Java application.

method A routine that belongs to a class.

method prototype The format of a method that specifies the name of the method, the return type, and the parameter list. A method prototype is also called a signature.

MIME Abbreviation for Multipurpose Internet Mail Extensions. The MIME specification supports electronic mailing of many kinds of messages (for example, audio files, images, and HTML).

modifier A Java keyword that is applied to a method or variable declaration to control access, control execution, or provide additional information. The keywords private, public, protected, final, native, synchronized, and volatile are Java modifiers.

multiple inheritance The ability for a class to inherit from multiple classes. Java does not support multiple inheritance.

multithreaded Having multiple threads of execution so that parts of a program can execute concurrently.

native methods Methods that are declared in Java with the keyword native but are implemented in another language. Usually, native methods are written to do something that the Java API does not already do, to interact with a particular computer's hardware or operating system or to improve performance. Since native methods are not portable across platforms, applets cannot contain native methods.

new The Java operator that is used to create a new instance of a class, for example, MyClass c = new MyClass().

object An instantiation of a class.

OOP Object-Oriented Programming-the ultimate extension of the concept of modular programming.

override To replace a method inherited from a superclass. For example, applets frequently override the init(), start(), stop(), destroy(), and paint() methods inherited from the applet class.

package A Java keyword used to assign the contents of a file to a package. Packages are Java's mechanism for grouping classes. Packages simplify reuse, and they are very useful for large projects.

pointers Variables that contain machine addresses of data instead of the data itself. The Java language does not support pointers.

private An access control modifier that limits access to within the class itself.

private protected An access control modifier that limits access to a class and its superclasses.

protected An access control modifier that limits access to a class, the package, and its subclasses. A subclass, however, cannot access a superclass's protected variables.

protocol handler A Java routine that interprets a protocol, generally for a browser.

public An access control modifier that allows access to a variable or method from anywhere.

Runnable interface An interface that allows a class the ability to run in a distinct thread without being a subclass of Thread.

scope Defines where a method or variable is visible. A variable defined in a method is visible only within the method; it has local scope. A variable or method defined within a class is visible inside the class; it has class scope.

ServerSocket A Java class that supports network connections for server objects.

SGML Standard Generalized Markup Language, the grandfather of HTML.

signature The format of a method. A signature specifies the name of the method, the return type, and the parameter list. Also called a method prototype.

Socket A Java class that supports the creation of network connections.

start() An applet method used to begin execution and resume execution after an applet has been temporarily stopped. Applets override this method when they need to do processing after a one-time initialization and anticipate stopping temporarily (for example, when the user leaves the applet's page) and restarting.

statement A Java construct that controls program flow, controls execution of critical sections of code, makes an assignment, imports a package, or declares membership in a package.

static A Java keyword used to indicate that a variable is a class variable, allocated once per class (for example, static int myinteger). When class variables change, they change for every instance of a class.

stop() An Applet method that is overridden to stop execution (for example, stop sounds when the user leaves the applet's page). Usually, stop() and start() are implemented together, so stop() should be implemented in a way that permits the start() method to resume execution.

streams Controlled flows of data from one source to another. Java supplies several classes to create and manage streams. Classes that handle input data are derived from class InputStream, and classes that handle output data are derived from class OutputStream.

string A sequence of characters enclosed in double quotes in the generic sense. In Java, strings are instances of the String class. Even the statement String mystring = "This is my string."; creates a String object.

stub Part of the interface between Java code and a native method. A stub allows a native method to access Java parameters, access Java class variables, and return data to Java.

subclass A class that inherits methods and variables from another class. The statement class SubClass extends SuperClass means that SubClass is a subclass of Superclass.

super A reserved word that refers to a class's immediate superclass.

super() Shorthand for the superclass's constructor method.

superclass A generalization of another class. X is a superclass of Y if Y inherits variables and methods from X.

synchronized A Java keyword that prevents more than one thread from executing inside a method at once.

this A reserved word that refers to the current class.

token The smallest unit in a language that a compiler can recognize.

type A specific kind of data in a program or programming language. In the Java statement int my_integer = 1;, the int keyword indicates that my_integer is an integer instead of some other data type.

virtual machine An abstract, logical model of a computer used to execute Java bytecodes. A Java virtual machine has an instruction set, registers, a stack, a heap, and a method area.

VRML Virtual Reality Modeling Language.

vspace An attribute of the HTML <APPLET> tag that specifies the amount of vertical space above and below the applet and the text on the page.