Release Team[oR] 2001 [x] java
Special Edition Using Java 2 Platform by Joseph L. Weber
ISBN: 0789720183
Que © 1998, 1414 pages A broad resource for those beginning to program in Java or expanding their skills.
Table of Contents
Colleague Comments
Back Cover
Synopsis by Rebecca Rohan Billed as a "tutorial reference," Special Edition Using Java 2 Platform is an unusual hybrid that's neither a typical course book nor an end-to-end glossary-style reference. Instead, the large volume is laid out in 13 broad Java topic areas, such as User Interface, Databases, and IO, plus additional chapters for JavaScript and Java Resources. Information on a topic usually starts with very basic information, then progresses to examples, though the book doesn't claim to cover every possibility, such as every stream class. If Special Edition has the information you need, it will be served in an unintimidating way. Tables and screen grabs are put to use throughout.
Table of Contents Special Edition Using Java 2 Platform - 4 Introduction - 8 Part I
Introduction to Java
Chapter 1
- What Java Can Do for You - 10
Chapter 2
- Java Design - 19
Chapter 3
- Installing The JDK and Getting Started - 37
Chapter 4
- JDK Tools - 49
Part II
The Java Language
Chapter 5
- Obejct-Oriented Programming - 61
Chapter 6
- HelloWorld!: Your First Java Program - 70
Chapter 7
- Data Types and Other Tokens - 81
Chapter 8
- Methods - 101
Chapter 9
- Using Expressions - 112
Chapter 10 - Control Flow - 122 Chapter 11 - Classes - 135 Chapter 12 - Interfaces - 165 Chapter 13 - Threads - 178 Chapter 14 - Writing an Applet - 195 Chapter 15 - Advanced Applet Code - 222 Chapter 16 - JAR Archive Files - 233
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Chapter 17 - Applets Versus Applications - 247 Chapter 18 - Managing Applications - 268 Part III
User Interface
Chapter 19 - java.awt: Components - 276 Chapter 20 - Exceptions and Events in Depth - 313 Chapter 21 - Containers and Layout Managers - 352 Chapter 22 - Graphics - 377 Chapter 23 - JFC–Java Foundation Classes - 409 Chapter 24 - Advanced JFC - 441 Chapter 25 - Images - 471 Chapter 26 - Java 2D Graphics - 501 Part IV
IO
Chapter 27 - Files, Streams, and Java - 531 Chapter 28 - Using Strings and Text - 570 Chapter 29 - Using Internationalization - 593 Chapter 30 - Communications and Networking - 604 Chapter 31 - TCP Sockets - 623 Chapter 32 - UDP Sockets - 641 Chapter 33 - java.net - 661 Chapter 34 - Java Security in Depth - 688 Chapter 35 - Object Serialization - 710 Chapter 36 - Remote Method Invocation - 722 Chapter 37 - Management API - 739 Part V
Databases
Chapter 38 - Databases Introduced - 762 Chapter 39 - JDBC: The Java Database Connectivity - 777 Chapter 40 - JDBC Explored - 800 Part VI
Component-Based Development
Chapter 41 - JavaBeans - 817 Chapter 42 - JavaIDL: A Java Interface to CORBA - 838 Chapter 43 - Java—COM Integration - 863 Part VII
Advanced Java
Chapter 44 - Java Media Framework - 875 Chapter 45 - Commerce and Java Wallet - 901 Chapter 46 - Data Structures and Java Utilities - 936 Chapter 47 - java.lang - 964 Chapter 48 - Reflection - 1013 Chapter 49 - Extending Java with Other Languages - 1027 Chapter 50 - Java Versus C(++) - 1041 Part VIII
Debugging Java
Chapter 51 - Debugging Java Code - 1060 Chapter 52 - Understanding the .class File - 1103 Chapter 53 - Inside the Java Virtual Machine - 1123
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Part IX
JavaScript
Chapter 54 - Java Versus JavaScript - 1147 Chapter 55 - Starting with JavaScript - 1157 Part X
Java Resources
Chapter 56 - Java Resources - 1185 Part XI
Appendix
Appendix A - What’s on the CD-ROM - 1191
Back Cover • • • • • • • • •
The most comprehensive Java 2 tutorial reference available Upgrade to JFC, the Swing Toolkit, and other new Java 2 technologies Learn how to use all the core Java APIs, including the new Collection interface Save time with professional programming techniques and proven code Create network applications Master object serialization, RMI, and the Management API Build powerful database applications using JDBC Learn JavaBeans, IDL, and COM integration Make your Java application secure About the Author
Joe Weber is a frequent contributor to a variety of Java books, magazines, and other resources. He has been working with Java full-time since its early alpha stages and has helped advise a number of Fortune 500 companies on the goals of Java. He has also helped to generate adoption in these organizations. Mr. Weber is a VP of MagnaStar, Inc., a Java consulting firm; serves as the senior technical advisor to Soren Technologies, a medical software company whose systems are written in Java; and currently is the director of the DocuLink product division for Xlink Corporation. Joe has also served on advisory committees and taught classes at universities in the Midwest. He continues to be a strong advocate for Java in the educational environment. Mr. Weber is a cofounder of the Javaology Magazine and has contributed articles to several other Java magazines.
Special Edition Using Java 2 Platform Joseph Weber
Copyright © 1998 by Que All rights reserved. No part of this book shall be reproduced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without written permission from the publisher. No patent liability is assumed with respect to the use of the information contained herein. Although every precaution has been taken in the preparation of this book, the publisher and author assume no responsibility for errors or omissions. Neither is any liability assumed for damages resulting from the use of the information contained herein.
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International Standard Book Number: 0-7897-2018-3 Library of Congress Catalog Card Number: 98-68732 Printed in the United States of America First Printing: January 1999 00
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Trademarks All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Que Publishing cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. Java is a trademark of Sun Microsystems, Inc.
Warning and Disclaimer Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied. The information provided is on an "as is" basis. The authors and the publisher shall have neither liability or responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book or from the use of the CD or programs accompanying it.
Credits Executive Editor Tim Ryan Acquisitions Editor Jeffrey W. Taylor Development Editor Benjamin Milstead Managing Editor Patrick Kanouse Project Editor Andrew Cupp Copy Editors Geniel Breeze Kelli Brooks Michael Brumitt Cheri Clark Keith Cline Dana Lesh Theresa Mathias San Dee Phillips Heather Urschel Indexer
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Erika Millen Technical Editors Joe Carpenter Jodi Cornelius Software Development Specialist Dan Scherf Production Carol Bowers Mona Brown Michael Dietsch Ayanna Lacey Gene Redding
Dedication To my parents, Emmet and Ruth, who taught me faith and dedication. I love them dearly.
About the Authors Joe Weber is a frequent contributor to a variety of Java books, magazines, and other resources. He has been working with Java full-time since its early alpha stages and has helped advise a number of Fortune 500 companies on the goals of Java. He has also helped to generate adoption in those organizations. Mr. Weber is a V.P. of MagnaStar Inc., a Java consulting firm; serves as the senior technical advisor to Soren Technologies, a medial software company whose systems are written in Java; and currently is the director of the DocuLink product division for XLink Corporation. Joe has also served on advisory committees for and taught classes at universities in the Midwest. He continues to be a strong advocate for Java in the educational environment. Mr. Weber is a cofounder of the Java™ology Magazine and has contributed articles to several other Java magazines. Mr. Weber loves to hear from his readers and can be reached via email at
[email protected] . Mark Wutka is a senior systems architect who refuses to give up his programming hat. For the past three years he has worked as the chief architect on a large, object-oriented distributed system providing automation for the flight operations division of a major airline. Over the past nine years, he has designed and implemented numerous systems in Java, C, C++, and Smalltalk for that same airline. He is currently Vice President of Research and Development for Pioneer Technologies, a consulting firm specializing in distributed systems and legacy system migration. He can be reached via email at
[email protected] . He also claims responsibility for the random bits of humor at www.webcom.com/wutka.
Acknowledgments I would like to thank and acknowledge the huge numbers of individuals who have worked on this book. A volume like the one that you hold in your hands right now is not the work of a single individual, but is a collaboration of the efforts of the writers, editors, and the developer. So many people contribute to a work like this behind the scenes, and unfortunately I don't even know all of their names, but their efforts are greatly appreciated. In particular I would like to thank Ben Milstead, who has developed this work and, along with Joe Carpenter and Jodi Cornelius, helped to insure that what you read is accurate. It would be impossible for this book to have the degree of accuracy that it has with out
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these people's efforts. I would like to thank Jeff Taylor, who was the last in a string of acquisition editors on this book, and who has stuck through it and made life so much easier. I would be remiss if I did not single out the efforts of Mark Wutka. Mark has helped to write portions of this book since its first edition and his skills and work have helped to add volume and understanding to this book. Mark deserves my immense gratitude and thanks for his contributions. I would also like to acknowledge Stephanie Gould, my first Acquistions Editor, who convinced me to work on my first book and showed me that I like writing. Mark Arend and Gene deGroot who, when I was not so much younger, each taught me perseverance and creativity. Shawn Gubine, my oldest and dearest friend, for reasons not even he probably knows. Scott Morris, who taught me that the correct answer to why most software works the way it does is, "because they didn't ask me," and that confidence is 99 percent of success. David and Dorothy, my siblings, who have added humanity. Finally, last, but most importantly, I would like to thank my wife, Kim, whose patience, understanding, and love have allowed this book to come into existence. Kim deserves as much credit as I for making this book happen.
Tell Us What You Think! As the reader of this book, you are our most important critic and commentator. We value your opinion and want to know what we're doing right, what we could do better, what areas you'd like to see us publish in, and any other words of wisdom you're willing to pass our way. As the Executive Editor for the Java team at Macmillan Computer Publishing, I welcome your comments. You can fax, email, or write me directly to let me know what you did or didn't like about this book—as well as what we can do to make our books stronger. Please note that I cannot help you with technical problems related to the topic of this book, and that due to the high volume of mail I receive, I might not be able to reply to every message. When you write, please be sure to include this book's title and author as well as your name and phone or fax number. I will carefully review your comments and share them with the author and editors who worked on the book. Fax:
317-817-7070
Email:
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Tim Ryan, Executive Editor Java Team Macmillan Computer Publishing 201 West 103rd Street
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Indianapolis, IN 46290 USA
Introduction Overview Welcome to the amazing and dynamic world of Java! If you are brand new to Java, you're in for a treat. Java is an extremely rich language that is simple and easy to learn. Java gives the programmer unprecedented access to even the most complex of tasks. What is Java? Java is a revolutionary programming language that was introduced by Sun Microsystems in June 1995. Since then, hundreds of thousands of programmers have picked up books just like the one you hold in your hands now and have realized just how powerful the language is. Java is an object-oriented programming language, which means that people programming in Java can develop complex programs with great ease. In addition, Java has built-in support for threads, networking, and a vast variety of other tools. A note about version numbers: The final release of Java in December 1998 was called Java 2. At that time, however, the JDK was still being called JDK 1.2. Don't be confused; JDK 1.2 is part of Java 2, and this book covers both.
This Book Is for You If you're new to Java, this book is for you. Don't be intimidated by the size of this book. It contains a vast amount of rich information about every facet of the Java programming language, along with easy-to-follow chapters that are designed to get you started. If you're already a Java expert, this book will become a treasured item on your shelf. Actually, it may never leave your desk. This book puts into one source the most complete reference and set of examples on every aspect of the Java programming language ever compiled. No currently available API has gone unexplored; no programming method has gone undocumented. Between the covers of this book, you find examples and explanations that will make your life as a programmer immensely easier.
How This Book Is Organized This book is organized into 11 parts. Each part covers a large chunk of information about how the Java programming language is organized. Part I, "Introduction to Java," introduces you to the design of the Java language and the Virtual Machine. It shows you what Java can do for you, and how it's being implemented in some programs today. Clear instructions have been included to help you get started by downloading the Java Development Kit and installing it. Finally, this part teaches you how each of the free tools included in the Java Development Kit (JDK) work. Part II, "The Java Language," shows how Java's syntax is developed. The fundamental aspects of Java are found in its language syntax. Every program is built using the fundamentals of the language, and this part walks you through each segment. The second half of this part talks about building specific Java programs, such as applets and applications. For the beginner, each of the chapters has been structured to help you become familiar with Java programming. For the expert, the individual aspects of the language are explored in great detail, making Part II a great reference as well as a learning tool. Part III, "User Interface," teaches you the details of building a graphical user interface in Java. It shows you how to do this using the traditional AWT interfaces, and then
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demonstrates the new features of Java 1.2 with the Java Foundation Classes (also know as Swing). In addition, this part explores how to build and manipulate images, and then discusses Java 1.2's 2D graphics system. Part IV, "IO," walks you through reading and writing data into your Java application. The part begins by teaching you the fundamental components and techniques of streaming and reading files. Then you learn how to build networked applications. You'll find priceless information about the internet's TCP/IP protocol. The part finishes by teaching you about the more advanced features, such as making sure your data transfers are secure. It covers using Java's serialization for sending and retrieving whole Java objects, and using Remote Method Invocation to run entire Java programs on remote machines. Finally, the part wraps up by discussing the new management API in Java 1.2 that allows you to talk to advanced devices, such as routers. Part V, "Databases," walks you through the details of one of the most important aspects of building modern business applications. Databases are the core to almost all business applications, and Java's JDBC (Java DataBase Connectivity) eases the burden of communicating between your Java applications and the database. In this part, you are introduced to how databases work, given a bit of history, and then you learn the terminology required to go on. Next, you explore Java's JDBC interface, which allows you to connect, send, and store data to any JDBC-compliant database. Welcome to the world of platform-independent and DBMS-independent systems! Part VI, "Component-Based Development," will be fascinating to anyone interested in learning how to make the development cycle faster and easier. Component-based development has been around for many years now, but it has never been as easy to do as with Java. In this part, you will learn how to use three different component models: Java's own JavaBeans specification, CORBA (which is rapidly becoming an industry standard, and maps very nicely to JavaBeans), and COM (Microsoft's interface for talking to Windows). Part VII, "Advanced Java," teaches you about some very complex technologies surrounding Java when you're ready to take the next step. Part VII shows you advanced techniques. You learn how to take advantage of the server-side capabilities of Java and how to use the Java Wallet for building commerce applications. You also learn about Java's built-in data structures and utilities, and how to build native applications. This part finishes with a comparison of Java to C++. Part VIII, "Debugging Java," teaches you all the tricks of the trade. This part will quickly become invaluable as you learn how important good debugging technique is when developing applications. You will find great references on every aspect of the sun.tools.debug package, as well as on the op-codes for Java's Virtual Machine. Part IX, "JavaScript," talks about the distant cousin to Java, JavaScript, which can help you do tasks with great ease. Because it can control the browser, it can even do some things Java can't. This part teaches you JavaScript programming, so you'll be multilingual. Part X, "Java Resources," is a perfect source for additional material beyond this book. You'll find some terrific Web sites and other material to help you stay up to date and on top of the Java community. Part XI, "Appendix," gives you an overview of all of the resources on the CD-ROM included with this book.
Conventions Used in This Book This book uses various stylistic and typographic conventions to make it easier to use. Note When you see a note in this book, it indicates additional information that may
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help you avoid problems or that should be considered in using the described features. Tip Tip paragraphs suggest easier or alternative methods of executing a procedure. Tips can help you see that little extra concept or idea that can make your life so much easier. Caution Cautions warn you of hazardous procedures (for example, activities that delete files). Special Edition Using Java 2 uses cross-references to help you access related information in other parts of the book. See "The Object Class."
Part I: Introduction to Java Chapter List Chapter 1: What Java Can Do for You Chapter 2: Java Design Chapter 3: Installing the JDK and Getting Started Chapter 4: JDK Tools
Chapter 1: What Java Can Do for You The Many Types of Java Applications By now you have probably heard enough hype about Java to go out and buy this book. The good news is that the hype is well-justified. Java is probably everything you have heard that it is and more. In this chapter, you examine the various possibilities provided by the Java language by taking a look at the different types of applications you can develop with it. To drive the point home, you then take a look at several examples of Java applets that are currently on the Web. You also examine examples of a Java Graphical User Interface (GUI) application and a Java command line application. By the end of this chapter, you should have a fairly good idea of what you can accomplish with Java and be excited about this language, the incredible new enhancements with JDK 1.2, and how Java is changing the computing world. Java is not used only to create applets or servlets. The amazing thing about Java is that it can be used to create a huge variety of applications. The following are a few of the types of applications you can build in Java: • Applets (mini applications) • GUI applications • Command line applications • Servlets (server side applications)
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• Packages (libraries) • Embedded applications (such as oscilloscopes and other embedded computers) • Pen-based programs Applets are essentially applications that run inside a Java-enabled browser, such as Netscape Navigator, Microsoft Internet Explorer, or HotJava. GUI applications developed in Java have graphical interfaces and stand on their own. They operate like any other GUI application, for instance the Windows Notepad application, which does not require a Web browser to execute it. Command line applications can be run from an MS-DOS command prompt or a UNIX shell prompt, just like the xcopy command in MS-DOS or the ls command in UNIX. Packages are not applications per se. Rather, packages are more like a collection of classes (portable Java-bytecode files) that belong to one package (similar to a C++ class library). There is no custom format for packages like those used with static and dynamic libraries on the various operating systems. The implementation in Java is much simpler and more portable. Basically, all classes belonging to a package are placed in one directory. For example, all classes belonging to Java's Abstract Window Toolkit (AWT) package, java.awt, are placed in a directory called AWT under the C:\jdk1.2\src directory. This is a directory tree of various packages provided with the Java Development Kit: c:\java\classes |___applet |___awt | |___Button.class | |___Color.class | |___Event.class |___io |___lang |___net |___util A few examples of class files under the AWT directory are also shown to illustrate the point here (in actuality, there are several dozen class files under the AWT directory).
Learning About the Java Language When Java was first created, Sun Microsystems released a white paper that described Java with a series of buzzwords to make your head spin: Java is a simple, object-oriented, robust, secure, portable, high-performance, architecturally neutral, interpreted, multithreaded, dynamic language. Phew! Try saying all that in one breath. Anyway, the language itself is discussed in more detail in the remainder of this book, but the one buzzword you need to learn for this chapter is interpreted. Java source code compiles into portable bytecodes that require an interpreter to execute them. For applets, this task is handled by the browser. For GUI and command line applications, the Java interpreter program is required to execute the application. The
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examples shown in the section "Java Command Line Applications" later in this chapter illustrate both methods.
The Java Development Kit The reason Java is so popular is not simply because of the benefits of the language itself. The rich sets of packages (or class libraries to you C++ programmers) that come bundled with the Java Development Kit (JDK) from Sun Microsystems also contribute to its popularity. These prewritten objects get you up and running with Java quickly, for two main reasons: • You do not need to develop the functionality they provide. • The source code is available for all. Here is a brief description of some of the more significant packages provided with Java: Package
Description
java.applet
Classes for developing applets.
java.awt
Abstract Window Toolkit (AWT) classes for the GUI interface, such as windows, dialog boxes, buttons, text fields, and more.
java.net
Classes for networking, URLs, client/server sockets.
java.io
Classes for various types of input and output.
java.lang
Classes for various data types, running processes, strings, threads, and much more.
java.util
Utility classes for dates, vectors, and more.
java.awt.image Classes for managing and manipulating images.
Java Applets As mentioned previously, Java applets run within a Java-enabled Web browser. Because Web browsers were primarily developed for displaying HTML documents, incorporating Java applets inside a Web browser requires an HTML tag to invoke an applet. This HTML tag is the
tag, as shown in the following example: tag for the applet, or the host name specified in the CODEBASE parameter of the tag. The numeric IP address of the host does not work. The previous strict set of restrictions on access to a local file system applies to applets running under Netscape Navigator. The JDK AppletViewer slightly relaxes the restrictions by letting the user define a specific, explicit list of files that can be accessed by applets. Now, as you will learn in Chapter 16, "JAR," it is possible to overcome the limitations on applets in 1.1-compliant browsers by "signing" the files. This enables applets that need to perform one of these functions this capability while maintaining a security framework. External Code Access Restrictions Applets cannot do the following: • Call external programs via such system calls as fork or exec. • Manipulate any Java thread groups except their own thread group that is rooted in the main applet thread. System Information Access Applets can read some system properties by invoking System.getProperty (String key). Applets under Netscape have unrestricted access to these properties. Sun's JDK AppletViewer enables individual control over access to each property. Table 2.2 lists the type of information returned for various values of key. Table 2.2 System Variable Availability tag onto the little Duke icon of the AppletViewer. You can also double-click the AppletViewer Duke icon and use one of the two Open menus to open an applet. The AppletViewer File menu contains the following options: tag? The tag is a new HTML tag that is used to include Java applets. When creating your own HTML files, don't forget to include the closing tag as well, or your applets won't appear. Note With Java files, it is necessary that the filename be the same as the class file. This is not necessary with the HTML file. In fact, a single HTML file can contain several tags. Listing 6.9 HelloApp.html—HTML File to Use for Applet tags in any given HTML file and opens a new window for each of them. When you run the HTML file in AppletViewer, you see output such as that in Figure 6.1. To run the HelloApplet program using AppletViewer, type appletviewer HelloApplet.html on the command line. OldRate ) * Interest; Try a very basic program to test some of what you have just learned. Listing 10.1 shows a list of printouts that tell if the things you learned in grade school were true. Here, we're using another convenient fact of Java—you can add Boolean values to a string and the answer true or false will be displayed for you. Listing 10.1 QuickTest.java—A Simple Lesson from the Third Grade public class QuickTest { public static void main(String args[]){ System.out.println("5 is greater than 6:"+(5>6)); System.out.println("6 is greater than or equal to 3:"+(6>=3)); System.out.println("8 is less than 10:"+(8<10)); } } To run this program, first copy Listing 10.1 to a file called QuickTest.java. As discussed in previous chapters, it's important the file be called QuickTest.java with all capitalization the same. Next, compile the program using javac: javac QuickTest.java After the file is compiled, you're ready to run it: java QuickTest As you may have already guessed, the output you get should look like this: 5 is greater than 6:false 6 is greater than or equal to 3:true 8 is less than 10:truen) If the left side of this expression produces the Boolean value true, then the result of the whole expression is true, regardless of the result of the comparison m>n. Note that in the following expression, if you instead used a bitwise operator, m and n are compared regardless of the values of x and y: (xn) The precedence of the two conditional operators is below that of the bitwise operators. tag (see Chapter 14, "Writing an Applet," to learn more about applets) or the Java program is run on an application (see Chapter 17, "Applets Versus Applications"), the virtual machine does a few things. In the case of an application, when you type java MyClass, the virtual machine calls the static method main() in MyClass. That doesn't actually create an instance of MyClass, but, because it's static (see the preceding note), an instance isn't necessary. That's why you typically need to create an instance of your class in the main() method. In the case of an applet, the browser does create an instance of MyClass when it encounters and automatically calls the init() method. Note One additional difference in Java between objects and primitive types is how they are referenced. Primitive types are always referred to by their value. Object types are always referred to by their reference. This means that in the following code, x and y are not equal at the end, but in w and z, myName is the same: int x = 5; int y = x; y++;numberofThreadsAtStart+2){ try{ thisThread.sleep(100);
tag in an HTML file, it will retrieve the class files for the applet from the server. The bytecode verifier then determines whether the class is a legitimate one. Assuming that the class is legit, the verifier will start to process the class file. As the VM detects import statements, it will continue to go back to the server for more class files until it has downloaded all the code for the applet. For a visual depiction of this cycle see Figure 14.1. tag on the third line. The tag is used to indicate to the browser that you want it to include an applet on your page. In many ways the tag is similar to the tag: CODE, HEIGHT, and WIDTH. Note Like most HTML tags, the tag is mostly case-insensitive. In other words, all three of the following tags perform the same thing: tag itself is case-insensitive, its attribute values are not. This means that you cannot enter GobLoader as gobloader or GOBLOADER. The first attribute of the tag is the CODE statement. The CODE value of is similar to the SRC value of , the CODE value must be set to the name of the main class file of the applet. In the case of Muncher, there are a number of classes, but the only one you should include in the HTML file is GobLoader.class (Muncher used to be called Gobbler, so the name is a hold over). This is important to realize; including the wrong class name can cause some strange and disastrous problems. It's also important to remember that having a CODE value is a required portion of an tag, unless an alternative OBJECT attribute is not present. Note Most applets come with either a description of which class file to include, or a sample HTML file you can look at to find this answer. Alternatively, the class name is the one thing you can see when viewing the HTML document source on another site. The second and third attributes to notice are the HEIGHT and WIDTH attributes. These are identical to those in the tag is the closing tag. The ending tag is required for an applet. In addition, as you will see in Listing 14.2, because the tag does not have an ALT attribute like tag can be used to include alternative information. Warning: You are not using a Java browser. There is an applet on this page you cannot see. If you had a Java-enabled browser you would see something similar to the picture below As you can see, you can include any standard HTML between the and tag. A non-Java browser will ignore the tag and only read this information. The . This HTML tag is This example demonstrates two important things. First note the and the tags. A . This is another example of an alternative display. If the viewer does not have a Java-enabled browser, the graphic will be displayed instead. In the case of GrayButton, this works out especially nice, because the only thing that is lost without a Java browser is the level of interaction. Attributes In addition to the attributes already mentioned, you can use several attribute values to further customize how an applet will behave, as shown in Table 14.1. Table 14.1 Attributes for the Tag tag but is unable to display the applet. Otherwise, the open HTML between the and tags is displayed. tag is located, are the only hosts that can be accessed by the applet. Tag parameters alternate-content tag. Java Plug-in is actually a different program for Internet Explorer altogether, so you need to include it just like any other ActiveX component. Listing 14.5 shows how Java Plug-in can be used in an HTML page designed for Internet Explorer, with the same applet used previously in Listing 14.3. Listing 14.5 Using Java Plug-in in Internet Explorer The tag in Listing 14.5 has many of the same attributes as the tag in Listing 14.3. There are some differences, however. First, and perhaps most obvious, is the CLASSID parameter. This ID identifies not the Java class, but rather the Java Plug-in. It should always be this number, so you don't have to worry about where this came from. The number will actually be different for each different version of the Java Plug-in, so you may need to find out what the latest version is and get its CLASSID. Now, the CODEBASE in the tag that you see is not the CODEBASE for the java class, but it's the CODEBASE for the Java Plug-in. Because both the code and CODEBASE parameters can't be specified in the tag itself, they end up in the and . <![CDATA[ No JDK 1.2 support for APPLET!! ]]> With the tag, the new parameter isn't CLASSID; instead it's the TYPE value. You might notice that there is a VERSION value in the type. The VERSION allows you to specify the Java version you wish to use. Note the PLUGINSPAGE parameter, which specifies where Netscape can find the plug-in if it hasn't already downloaded it. One of the interesting things about using an tag is that there are no equivalents to the tag itself. Look at the LINK parameter for an example of how this is used. and tags as shown in Listing 14.7 so that both Netscape and Internet Explorer will use Java Plug-in. Listing 14.7 Using Java Plug-in in Both Internet Explorer and Netscape <![CDATA[ </COMMENT> No JDK 1.2 support for APPLET!! ]]> <![CDATA[<XMP>'); else if (_ns == true) document.writeln('<EMBED TYPE="application/x-java-applet;version=1.1" WIDTH="200" HEIGHT="200" ALIGN="baseline" CODE="gray.class" CODEBASE="html/" GRAPHIC=http://www.magnastar.com/NOW.GIF LINK ="http://www.magnastar.com/GrayButton/license.html" pluginspage="http://java.sun.com/products/plugin/1.1/plugininstall.html"> <NOEMBED><XMP>'); //—></SCRIPT> <APPLET CODE="gray.class" CODEBASE="html/" ALIGN="baseline" WIDTH="300" HEIGHT="300" rel="nofollow"></XMP> <PARAM NAME="code" VALUE="gray.class"> <PARAM NAME="codebase" VALUE="html/"> <PARAM NAME="graphic" VALUE ="http://www.magnastar.com/NOW.GIF"> <PARAM NAME ="link" VALUE="http://www.magnastar.com/GrayButton/license.html"> No JDK 1.2 support for APPLET!! </APPLET>]]> In addition to these files, you will also need to have several images that you want to animate, and you will need to place them in a subdirectory called images. The images must be called img1.gif, img2.gif, and so on, where img1.gif is the first image of the animation. You will also want to change the imgNumber parameter to have the correct number of images. With all that done, you should see something similar to Figure 14.10.Applet Test Page Applet Test Page tag included in HTML files. In addition, you learned that the syntax for a tag to load an applet from a similar ZIP file. Starting with version 3.0, Microsoft Internet Explorer started allowing you to load Java applets from Microsoft's CAB files, like ActiveX controls. JAR files have been replacing these other mechanisms over time. They offer the following benefits which make them the preferred choice. tag, JAR archives can be used transparently with existing Java applets, with no change to the applet code. . 10:04a .. 11:29a audio 12:34p 139 example1.html 11:29a images 12:34p 3,454 TicTacToe.class 10:27a 7,593 TicTacToe.java 7 File(s) 11,186 bytes 1,575,772,160 bytes free the CODEBASE attribute indicates the URL base from which to load the class file. If no CODEBASE is specified, the URL of the referring page is used. For example, the browser will try to load the following applet from http://www.foo.com/applets/FooMain.class: ... Beginning with JDK 1.1, Sun specified changes to the tag which enable the class to be loaded from a JAR archive that is downloaded before the Java applet class is located. Loading from a JAR archive can be specified in two ways: using an attribute or using a parameter. First, an attribute named ARCHIVES can be used, as follows: ... When the browser reads this tag, it first downloads the Foo.jar file from the server, then tries to find the FooMain.class in Foo.jar. If the browser cannot find the class in the archive, it looks at the location specified by the CODEBASE, as usual. Alternatively, the JAR archive can be specified as a parameter. This parameter should have the name ARCHIVES. The parameter's value is the name of the JAR file, as follows: It's possible to specify more than one JAR archive to be loaded. To do so, insert the string + (a plus sign surrounded by spaces) between the archive filenames, as follows: ... Specifying a JAR archive in an APPLET tag is a performance optimization, instructing the browser to preload a specified archive and use that archive, if possible, when locating classes. If the JAR file is not found, or if a required class file is not found in the archive, the usual search procedure, as defined by JDK 1.0, will be followed. Specifying a JAR file to preload does not prevent the usual search paths from being tried and used if necessary. tag used by the TicTacToe demo in JDK 1.1. The file example1.html, in Listing 16.1, contains this tag. LISTING 16.1 example1.html—Without JAR Archive Loading TicTacToe The source. Copy this to the subdirectory jar that you created previously. D:\JDK1.2\demo\TicTacToe>copy example1.html jar 1 file(s) copied. Now edit it to add the APPLETS attribute. It should look like Listing 16.2 when you're done. LISTING 16.2 example1.html—With JAR Archive Loading TicTacToe The source. Now you should be able to run the TicTacToe applet from the JAR archive created earlier: D:\java\demo\TicTacToe\jar>appletviewer example1.html loading d:\jdk1lb2\java\bin\..\lib\awt.properties"); System.out.println("\n\nWhere is the person to greet"); } else System.out.println("Hello "+args[0]+"!"); } } Now, if you happen to run the Hello World program without any parameters, what you will see should look like this: Syntax for running Hello is: java Hello is the person to greetClock Clock (JPanel.java:50) at javax.swing.JPanel.(JPanel.java:83) at javax.swing.JRootPane.createGlassPane(JRootPane.java:145) at javax.swing.JRootPane.(JRootPane.java:112) at javax.swing.JFrame.createRootPane(JFrame.java:105) at javax.swing.JFrame.frameInit(JFrame.java:99) at javax.swing.JFrame.(JFrame.java:93) at HelloWorldJFC.main(HelloWorldJFC.java:41) If you do see this, you have failed to add the Windows look and feel (or whichever one you're having problems with) to the classpath. Because the individual look-and-feels are packaged in separate JAR files, all you need to do is add the required JAR file to your classpath.Applet Test Page Applet Test Page Applet Test Page Applet Test Page Applet Test Page Applet Test Page [email protected] indicates "send mail to user 'dwb' at the machine netspace.org," ftp://[email protected] / means "open an FTP connection to netspace.org and log in as user dwb."". first = hitPage.indexOf("") + "".length(); first = hitPage.indexOf("". last = hitPage.indexOf(" "); // If our beginning is after our end, return. if (last < first) { return hitSection; } // If neither substring is found, return. if (first == notFound || last == notFound) { System.err.println("Bad search page format"); return hitSection; } // Cut out the substring. hitSection = hitPage.substring(first,last); first = last = 0; totalHits += 1; // Found one hit. // Go through the page line by line. while((last = hitSection.indexOf("\n",first)) != notFound) { // Find the next "\n\n\n" + AGENT_NAME + " \n\n\n" + "Search Results \nTotal number of " +
\n\n" + outputList + " \n\n\n"); } } The main() Method: Starting the Application First, the application imports the two packages it will be using, allowing its method invocations of the Java API to be more brief. Then the class is declared and a number of private instance variables are initialized: search_URL is the URL to the AltaVista search engine, totalHits maintains a count of the hits returned, and outputList is a buffer for the HTML of the returned hits. The main() method enables this code to be executed as an application. This method checks for an appropriate set of arguments and creates an instance of the AltaVistList class. It then tells that instance to print its output, passing the printOutput() method System.out. System.out is a static reference to a PrintStream object within the java.lang.System class. By passing this PrintStream to printOutput(), it indicates that the AltaVistaList instance should send its data to standard output. Finally, main() exits the application with a return value of 0, indicating that the execution completed normally. The AltaVistaList Constructor The class' only constructor takes an argument of a reference to an array of String objects. It passes this array reference to the createQuery() method, described below, which builds a query for the AltaVista search engine. The constructor then invokes a static method of the URLConnection class, setDefaultRequestProperty(): URLConnection.setDefaultRequestProperty("User-Agent", AGENT_NAME + "/" + AGENT_VERSION); Note that because this is a static method, it is not invoked through an instance of URLConnection. Instead, the method is invoked through the class itself. This method indicates that all HTTP requests should specify the "User-Agent" field as being equal to a string that identifies this application. The HTTP User-Agent is a field that Web clients use to tell servers their program name, allowing servers to keep track of what clients are visiting the site. For instance, Netscape browsers send a User-Agent field that includes "Mozilla," while the Internet Explorer sends "Explorer." Unfortunately, as of the writing of this chapter, the JDK has yet to implement this method, and the UserAgent remains the default Java. This code has been left in with the assumption that the JDK will soon complete its implementation of the Java API. The constructor then enters an infinite loop. In this loop, it calls the getPage() method with an URL of a page to receive. This URL is the URL of the AltaVista search engine appended by a question mark, the query returned by createQuery(), and a number from where the hit list should start. AltaVista lists hits 10 at a time, and the startHits counter enables the AltaVistaList application to increment throughout the entire list of hits. The returned page is passed to getHits(), which strips out the hits from the rest of the HTML page. If what remains is a null String reference, the application breaks from the loop. Otherwise, it appends the data to a StringBuffer and then increments the startHits counter to set up for retrieving the next ten hits. The createQuery() Method: Building the Query String This protected method is used internally by an instance of the AltaVistaList class, building the query syntax for the AltaVista search engine. This query string follows this format: what=web&fmt=c&pg=q&q=&stq=, which is where the hit list should begin. The end of the hit list should be at the first tag. If no such string is found, the method returns with a null String reference, indicating that the page was devoid of hits. Otherwise, the method pares down the HTML page to a substring and iterates through that data. Each hit should be a new line starting with
*/ public static void main(String[] args) { if (args.length < 2) { System.out.println( "Usage: StockQuoteClient "); System.exit(1); } StockQuoteClient client = new StockQuoteClient(args); client.printQuotes(System.out); System.exit(0); } /** * This constructor manages the retrieval of the * stock information. * @param args The server followed by the stock IDs. */ public StockQuoteClient(String[] args) { String serverInfo; // Server name is the first argument. serverName = args[0]; // Create arrays as long as arguments - 1. stockIDs = new String[args.length-1]; stockInfo = new String[args.length-1]; // Copy the rest of the elements of the args array // into the stockIDs array. for (int index = 1; index < args.length; index++) { stockIDs[index-1] = args[index]; } // Contact the server and return the HELLO message. serverInfo = contactServer(); // Parse out the timestamp, which is everything after // the first space. if (serverInfo != null) { currentAsOf = serverInfo.substring( serverInfo.indexOf(" ")+1); } getQuotes(); // Go get the quotes. quitServer(); // Close the communication. } /** * Open the initial connection to the server. * @return The initial connection response. */ protected String contactServer() { String serverWelcome = null; try { private static final File STOCK_QUOTES_FILE = new File("stockquotes.txt"); private ServerSocket listenSocket = null; private Hashtable stockInfo; private Date stockInfoTime; private long stockFileMod; // A boolean used to keep the server looping until // interrupted. private boolean keepRunning = true; /** * Starts up the application. * @param args Ignored command line arguments. */ public static void main(String[] args) { StockQuoteServer server = new StockQuoteServer(); server.serveQuotes(); } /** * The constructor creates an instance of this class, * loads the stock data, and then our server listens * for incoming clients. */ public StockQuoteServer() { // Load the quotes and exit if it is unable to do so. if (!loadQuotes()) System.exit(1); try { // Create a listening socket. listenSocket = */ public static void main(String[] args) { // This must be the same port and IP address used // by the receivers. if (args.length != 2) { System.out.print("Usage: MultiCastSender " + " \n\t can be one of 224.x.x.x " + "- 239.x.x.x\n"); System.exit(1); } MultiCastSender send = new MultiCastSender(args); System.exit(0); } /** * The constructor does all of the work of opening * the socket and sending datagrams through it. * @param args Program arguments - */ public MultiCastSender(String[] args) { DatagramPacket mcastPacket; // UDP datagram. String nextLine; // Line from STDIN. byte[] mcastBuffer; // Buffer for datagram. byte[] lineData; // The data typed in. int sendLength; // Length of line. */ public static void main(String[] args) { // This must be the same port and IP address // used by the sender. if (args.length != 2) { System.out.print("Usage: MultiCastReceiver \n\t can be one of " + "224.x.x.x - 239.x.x.x\n"); System.exit(1); } MultiCastReceiver send = new MultiCastReceiver(args); System.exit(0); } /** * The constructor does the work of opening a socket, * joining the multicast group, and printing out * incoming data. */ public MultiCastReceiver(String[] args) { DatagramPacket mcastPacket; // Packet to receive. byte[] mcastBuffer; // byte[] array buffer InetAddress fromIP; // Sender address. int fromPort; // Sender port. String mcastMsg; // String of message. try { // First, set up your receiving socket. mcastIP = InetAddress.getByName(args[0]); mcastPort = Integer.parseInt(args[1]); mcastSocket = new MulticastSocket(mcastPort); // Join the multicast group. mcastSocket.joinGroup(mcastIP); } catch(UnknownHostException excpt) { System.err.println("Unknown address: " + excpt); System.exit(1); } catch(IOException excpt) { System.err.println("Unable to obtain socket: " + excpt); System.exit(1); } while (keepReceiving) { try { // Create a new datagram. mcastBuffer = new byte[DATAGRAM_BYTES]; mcastPacket = new DatagramPacket(mcastBuffer, mcastBuffer.length); // Receive the datagram. mcastSocket.receive(mcastPacket); fromIP = mcastPacket.getAddress(); fromPort = mcastPacket.getPort(); mcastMsg = new String(mcastPacket.getData()); // Print out the data. System.out.println("Received from " + fromIP + " on port " + fromPort + ": " + mcastMsg); } catch(IOException excpt) { System.err.println("Failed I/O: " + excpt); } } try { mcastSocket.leaveGroup(mcastIP); // Leave the group. } catch(IOException excpt) { System.err.println("Socket problem leaving group: " + excpt); } mcastSocket.close(); // Close the socket. } /**.Handler. If you open an HTTP URL, for instance, the URL class searches for a class named .http.Handler. By default, the class only searches the package sun.net.www.protocol, but you may specify an alternate search path by setting the system property to java.protocol.handler.pkgs. This property should contain a list of alternate packages to search that are separated by vertical bars. For example: mypackages.urls|thirdparty.lib|funstuff" At the minimum, any subclass of the URLStreamHandler must implement an openConnection method: protected abstract URLConnection openConnection(URL u) throws IOException This method returns an instance of URLConnection that knows how to speak the correct protocol. If you create your own URLStreamHandler for the FTP protocol, for.major.minor. The major and minor names come from the MIME Content-type header, which is in the following form: Content-type: major/minor One of the most common major/minor combinations is text/plain. If you define your own text/plain handler, it can be named MyPackage.text.plain. By default, the URLConnection class searches for content handlers only in a package named sun.net.www.content. You can give additional package names by specifying a list of packages separated by vertical bars in the java.content.handler.pkgs system property. The only method you must implement in your ContentHandler is the getContent method: public abstract Object getContent(URLConnection urlConn) throws IOException It is completely up to you how you actually parse the content and select the kind of object) and SQLAllocConnect(,). After you get a valid database handle, you can set various options using SQLSetConnectOption(, ,). Then you can connect to the database using SQLConnect(,,, .. etc.). The ODBC Command Sequence Now you are ready to work with statements. Figure 38.3 shows the ODBC command sequence to connect to a database, execute a SQL statement, process the result data, and close the connection., ). After the statement handle is allocated, you can execute SQL statements directly using the SQLExecDirect function, or you can prepare a statement using SQLPrepare and then execute with the SQLExec function. You first bind the columns to program variables and then read these variables after a SQLFetch statement for a row of data. SQLFetch returns SQL_NO_DATA_FOUND when there is no more data. Note JDBC also follows similar strategy for handling statements and data. But JDBC differs in the data binding to variables. Now that you have processed the data, it is time to deallocate the handles and close the database by using the following statement sequence: SQLFreeStmt(, ..) SQLDisconnect(); SQLFreeConnect(); SQLFreeEnv(); Note In JDBC, the allocate statements and handles are not required. Because Java is an object-oriented language, you get the connection object, which then gives you the statement object. As Java has automatic garbage collection, you don't need to free handles, delete objects, and so on. When an object loses scope, the JVM will reclaim the memory used by that object as a part of the automatic garbage collection. WHERE CURRENT OF The positioned UPDATE statement to update the fields in the current row is SET = WHERE CURRENT OF The positioned DELETE statement to delete the current row takes the form DELETE WHERE CURRENT OF Generally, for this type of SQL statement to work, the underlying driver or the DBMS has to support updatability, concurrency, and dynamic scrollable cursors. But there are many other ways of providing the positioned UPDATE/DELETE capability at the application program level. Presently, JDBC doesn't support any of the advanced cursor functionalities. However, as the JDBC driver development progresses, I am sure there will be very sophisticated cursor management methods available in the JDBC API.: For databases on the Internet or intranet, the subname can contain the Net URL //hostname:port/. The can be any name that a database understands. The odbc subprotocol name is reserved for ODBC-style data sources. A normal ODBC database JDBC URL looks like the following: jdbc:odbc:;User=;PW= If you are developing a JDBC driver with a new subprotocol, it is better to reserve the subprotocol name with Sun, which maintains an informal subprotocol registry.:port/ URL or just a data source name used by the ODBC driver or a full pathname to a database file in the local computer. For all you know, it could be a pointer to data feed of the stock [, ...]} The CallableStatement class supports parameters. These parameters are of the OUT kind from a stored procedure or the IN kind to pass values into a stored procedure. The parameter marker (question mark) must be used for the return value (if any) and any output arguments because the parameter marker is bound to a program variable in the stored procedure. Input arguments can be either literals or parameters. For a dynamic parameterized statement, the escape clause string takes the form {[? =] call [, ...]} The OUT parameters should be registered using the registerOutparameter() method (see Table 40.4) before the call to the executeQuery(), executeUpdate(), or execute() methods.( value ); public get(); public boolean is(); Note that the last pattern is an alternative getter method for Boolean properties only. setter methods are allowed to throw exceptions if they so choose. The accessor methods for the TextDisplayer Bean are shown in Listing 41.3. Notice that all the accessor methods have been declared as synchronized. Even though nothing serious could happen in this Bean, you should always assume that your Beans are running in multithreaded environments. Using synchronized accessor methods helps prevent race conditions from forming. You can check the TextReader.java file on your CD-ROM to see the accessor methods for the TextReader Bean. Listing 41.3 TEXTDISPLAYER.JAVA—The Accessor Methods for the Properties in the TextDisplayer Bean public synchronized String getOutputText() { return( OutputText ); } public synchronized void setOutputText( String text ) { OutputText = text; resizeCanvas(); } public synchronized Color getBGColor() { return( BGColor ); } public synchronized void setBGColor( Color color ) { BGColor = color; setBackground( BGColor ); // set the Canvas's background color. repaint(); } public synchronized Font getTextFont() { return( TextFont ); } public synchronized void setTextFont( Font font ) { TextFont = font; setFont( TextFont ); // set the Canvas's font. resizeCanvas(); } public synchronized Color getFontColor() { return( FontColor ); } public synchronized void setFontColor( Color color ) { FontColor = color; setForeground( FontColor ); // set the Canvas's foreground color. get( int index ); void set( int index, value ); [] get(); void set( [] value );Listener( PropertyChangeListener l ); public void removeListener( PropertyChangeListener l ); Beans wanting to bind to other components' properties should implement the PropertyChangeListener interface, which consists of the following method: public void propertyChange( PropertyChangeEvent evt ); Whenever a bound property in a Bean is updated, it must call the propertyChange() method in all the components that have registered with it. The class java.beans.PropertyChangeSupport is provided to help you with this process. The code in Listing 41.4 shows you what is required in the TextReader Bean to allow its InputText property to be bound. Listing 41.4. TEXTREADER.JAVA—Code Required to Make the InputText Property of the TextReader Bean a Bound Property // setter method for the InputText property. public synchronized void setInputText( String newText ) { String oldText = InputText; InputText = newText; setText( InputText ); changeAgent.firePropertyChange( "inputText", new String( oldText ), new String( newText ) ); } // these two methods allow this Bean to have bound properties. public void addPropertyChangeListener( PropertyChangeListener l ) { changeAgent.addPropertyChangeListener( l ); } public void removePropertyChangeListener( PropertyChangeListener l ) { changeAgent.removePropertyChangeListener( l ); } protected PropertyChangeSupport changeAgent = new PropertyChangeSupport( this );Listener( VetoableChangeListener l ); public void removeListener( VetoableChangeListener l ); Beans intended to constrain other components' properties should implement the VetoableChangeListener interface, which consists of the following method: public void vetoableChange( PropertyChangeEvent evt ); Whenever a constrained property in a Bean is updated, it must call the vetoableChange() method in all the components that have registered with it. There is also a support class to help make this process easier. Use the class java.beans.VetoableChangeSupport to help manage your vetoable properties. The code in Listing 41.5 shows you what is required in the TextReader Bean to allow its Width property to be constrained. Listing 41.5 TEXTREADER.JAVA—Code Required to Make the Columns Property of the TextReader Bean a Constrained Property // setter method for the Columns property. public synchronized void setWidth( int newWidth ) throws PropertyVetoException { int oldWidth = Width; vetoAgent.fireVetoableChange( "width", new Integer( oldWidth ), new Integer( newWidth ) ); // no one vetoed, so change the property. Width = newWidth; setColumns( Width ); Component p = getParent(); if ( p != null ) { p.invalidate(); p.layout(); } changeAgent.firePropertyChange( "width", new Integer( oldWidth ), new Integer( newWidth ) ); } // these two methods allow this Bean to have constrained properties. public void addVetoableChangeListener( VetoableChangeListener l ) { vetoAgent.addVetoableChangeListener( l ); } public void removeVetoableChangeListener( VetoableChangeListener l ) { vetoAgent.removeVetoableChangeListener( l ); }( must inherit from java.util.EventObject. Here is an example of an event handler for a DinnerServedListener interface: void dinnerServed( DinnerServedEvent evt ); // DinnerServedEvent inherits from // java.util.EventObject. There is no restriction preventing an event handler method from throwing an exception. In addition, any one Listener interface can have any number of related event handlers. There are two types of events that components can listen for: multicast events and unicast events.( listener ); public synchronized void remove( listener ); The keyword synchronized is not actually part of the design pattern. It is included as a reminder that race conditions can occur, especially with the event model, and precautions must be taken.( listener ) throws java.util.TooManyListenersException; public synchronized void remove( listener ); unboundedBools; sequence boundedChars; }; }; The arrays would be defined in Java as public int[] longArray; public boolean[] unboundedBools; public char[] boundedChars; You now have two options for running BasicPlayer. First, you can use Netscape 4.03 with the final JDK 1.1 patch, or Internet Explorer 4, and if you have properly installed the media files from your vendor, you can now open the BasicPlayer.html file. The second option is to use the Appletviewer program included with the JDK. To use Appletviewer, first make sure that you still have the media.zip file included in your classpath, and then simply run it the way you are used to: Appletviewer BasicPlayer.html If everything has gone as planned, you should see and hear the promotional Intel video start to play eventually. CCAdmin.Type_Name */ public String getType () { return CCAdmin.TYPE_NAME; } /** * Returns the name the user associated with the specific instance * of the credit card * @return The local (wallet name) name of the credit-card. */ public String getName() { return localAlias;} /** * Set the user-defined name of this instance of the credit card. * @param x The local alias (wallet name) name of the creditcard. */ The container passed to this method is probably, but not * necessarily a Frame or an Object that inherets Frame. * (NOTE: Never cast this Container to Frame) * * The container may change dimensions. It is expected that the * User will resize the Window, causing this container to resize * as a result. The UI must be written to accommodate this (i.e. * stretch). * * Do not rely on any characteristics of any AWT components that * may exist above this Container. Those characteristics are * subject to change at any time, forcing any cassettes that rely * upon them to become obsolete. * * The populate method may be populating a live AWT component * (i.e. already shown). * * * @param c The container that the WalletUI should be drawn within. */ public void populate(Container c) { masterContainer = new CWPanel(context); c.setLayout(new BorderLayout(0,0)); /* Header for class SayHello1*/ #ifndef _Included_SayHello1 #define _Included_SayHello1 #ifdef __cplusplus extern "C" { #endif /* * Class: SayHello1 * Method: greet * Signature: ()V */ JNIEXPORT void JNICALL Java_SayHello1_greet (JNIEnv *, jobject); #ifdef __cplusplus } #endif #endif JNIEXPORT# void JNICALL# Java_SayHello1_greet ( JNIEnv *env, jobject this) { printf("Hi folks! Welcome to the netherworld of native methods!\n"); } JNIEXPORT# void JNICALL# Java_SayHello2_greet ( JNIEnv *env, jobject this) { jfieldID jf; jclass jc; jobject jobj; const jbyte *pal; JNIEXPORT# void JNICALL# Java_SayHello3_greet ( JNIEnv *env, jobject this) { jmethodID jm; jclass jc; jobject jo; const jbyte *area; jint x,y ; x =20; y =20; jc = (*env)->GetObjectClass(env, this); jm = (*env)>GetMethodID(env,jc,"rectArea","(II)Ljava/lang/ String;",x,y); jo= (*env)->CallObjectMethod(env,this,jm,x,y); area = (*env)->GetStringUTFChars(env,jo,0); printf("%s\n",area); } The Java class file and shared library is created as before, and on execution, you get this output: The Area of the Rectangle is 400 units Object methods can be called from within native methods by following these five steps: 1. Get the class type of the invoking object. 2. Get the method ID. 3. Initialize the variables that need to be passed as parameters to the Java method. 4. Use the appropriate CallMethod() accessor function to invoke the method. 5. Convert the returned object field as needed for use within the native method. Looking at the type signatures in Table 49.1, you can deduce that the type signature for the Java method rectArea() in Listing 49.6 is (II)Ljava/lang/String;. This is because the method takes in two ints and returns back a String object. Table 49.5 shows the various CallMethod() accessor functions that are available. Table 49.5 Accessor Functions to Invoke Java Methods from Native Methods #define PLAYERS 2 class Game { public: Game() { cout << "Constructing the Game\n"; } }; Now look at the Java equivalent: import java.lang.*; class Game{ public Game() { System.out.println ("Constructing the Game"); } public static final int PLAYERS=23; } Notice how the import statement appears to take the place of the #include. The two statements are superficially similar, but in fact accomplish quite different objectives. The #include does a straight source file inclusion on the part of the C pre-processor. Because the pre-processor doesn't understand C syntax (it's basically a batch-mode text editor), the source file being included could contain anything. The import statement tag can be replaced with any of the native types using proper capitalization (for example, RemoteBoolean for Boolean), as described in Table 51.10. Listing 51.9 Public API for the Set of RemoteXXX Classes public class extends RemoteValue { public get(); public String toString(); public String typeName(); } Table 51.11 lists each of the public member methods and what they do. Table 51.11 The RemoteXXX Class Public Member Methods designator as shown in Listing 51.9 may be replaced with any type from the Native Type column of Table 51.10 based on the actual RemoteXXX class that the current instance represents. For example, a RemoteBoolean class returns a real boolean value from its get( ) method. at your command prompt. JDB then performs its initialization and presents you with a > prompt. In fact, three "formal" command lines start JDB in various modes, as follows: 1. Start JDB and create a VM instance on this machine with no class loaded: JDB [-dbgtrace] [] Option]. That way, you can filter them in your printToConsole implementation and send loaded: JDB [-dbgtrace] [] [] Option This mandatory argument is the .class file to load initially into the JVM and control by the debugger. Use the run command to begin execution. . It must be specified here, as there is no way to set up arguments for 's main method after JDB starts up.] -password Option to start System.out.print( "MTTest: Press the key to begin." ); System.out.flush(); try { System.in.read(); } catch (java.io.IOException e) {} System.out.println(""); // Create the thread group theGroup = new ThreadGroup( "MTThreads" ); // Create the thread array theThreads = new MTTest[3]; // Create and start the threads for (int i = 0; i < theThreads.length ; ++i) { theThreads[i] = new MTTest( theGroup, "T" + Integer.toString(i)); if (theThreads[i] != null) theThreads[i].start(); } } } One of the first things to know about debugging anything with JDB that is multithreaded is that it is best to have the target application wait until you are ready and run it in a separate process space. Running in a separate process space prevents the target application's output from getting interspersed with the debugger output. Also, having the application wait for you means that it won't start running as soon as you start up the JVM that will run your application. To follow along with the examples associated with each command, complete the following steps: 1. Use the following command line to compile MTTest with debug information (line numbers and local variable information): javac Uses: RemoteDebugger.findClass() load causes the remote JVM to search for and load . If you do not fully qualify the name of the class to load, the VM tries to look in well-known packages to complete the name. If the class is not found, an error message is returned. Also, an error message is displayed if no is provided. This command does not affect the current context. run Syntax: run [ [args] ] Uses: RemoteClass.getQualifiedName and RemoteDebugger.run() This command loads and begins execution of or the last specified on the previous call to the run command. Error messages are returned if the class can't be found or if there is a general failure in attempting to start . This command also sets the context by establishing initial values for the currentThreadGroup and currentThread. threadgroup Syntax: threadgroup Uses: RemoteDebugger.listThreadGroups and RemoteThreadGroup.getName This command establishes as the default thread group by putting a reference to its RemoteThreadGroup instance in the currentThreadGroup instance variable. This command is required for using any of the commands that are relating to breakpoints, exception, and thread management. For example, you could enter: >threadgroup MTThreads to specify the current default thread group. thread Syntax: thread is an integer constant representing a thread's ID number. (See the threads command.) Uses: RemoteThreadGroup.listThreads This command sets as the current thread in context relative to the current thread group by putting a reference to its RemoteThread instance in the currentThread instance variable. This command is required for using any of the | $s | 0x | t@ represents a valid thread ID within the current thread group; $s represents the slot/offset to a variable in a stack frame; 0x represents represents the literal this, a valid class name, a field name (for example, class.field), an argument name, or a local variable name. Uses: RemoteThreadGroup.listThreads, RemoteThread.getStackVariables, RemoteStackVariable.getValue, RemoteDebugger.get, and RemoteDebugger.findClass This command dumps the detailed description of the specified thread, stack-based variable, class, field, named local variable, or named argument. If an argument, variable, or field is requested, its name and value are displayed. If a thread or class is specified, a detailed description of the thread or class is displayed, including instance variables and their current values. The following is an example of dumping the MTTest class: // Could also have entered: dump 0x1393768 "MTTest" is not a valid field of (MTTest)0x13a0ca8 MTTest = 0x1393768:class(MTTest) { superclass = 0x1393008:class(java.lang.Thread) loader = null private static Thread activeThreadQ = null private static int threadInitNumber = 2 public static final int MIN_PRIORITY = 1 public static final int NORM_PRIORITY = 5 public static final int MAX_PRIORITY = 10 static int count = 0 } T0[1] Note that the second line is a result of the search algorithm used by the dump command. list Syntax: list [line number] Uses: RemoteThread.getCurrentFrame, StackFrame.getRemoteClass, RemoteClass.getSourceFileName, RemoteClass.getGetSourceFile This command displays one or more source lines for the current thread's current method. There must be a thread in context that is running but in a suspended state. Also, the line number, if specified, must be relative to the top of the source file that defines the current method. Otherwise, if you don't specify a line number, then the current line is displayed. This listing includes the four lines of source immediately before and after the specified line. The following is how a list with no arguments should look for MTTest at the current breakpoint: T0[1] list 6 7 8 9 10 => 11 | 0x Uses: RemoteDebugger.get, or RemoteDebugger.findClass and RemoteClass.getMethods This command displays all of the methods in the specified class, including the signature of each. The methods list for MTTest should look like this: T0[1] methods MTTest void (ThreadGroup, String) void run() void main(String[]) T0[1] The method is a special name and represents the constructor for this class. print Syntax: print t@ | $s | 0x | t@ represents a valid thread ID within the current thread group; $s represents the slot/offset to a variable in a stack frame; 0x represents the numeric identifier for a currently loaded class; represents the literal this, a valid class name, a field name (for example, class.field), an argument name, or a local variable name. Uses: RemoteThreadGroup.listThreads, RemoteThread.getStackVariables, RemoteStackVariable.getValue, RemoteDebugger.get, and RemoteDebugger.findClass ] Uses: RemoteThreadGroup.listThreads, RemoteThread.dumpStack, and RemoteStackFrame.toString This command displays the call stack (the list of methods that were called to get to this point) for the current thread (as set with the thread command), all threads (for the.method | 0x.method Uses: RemoteDebugger.findClass or RemoteDebugger.get, RemoteClass.getMethod, and RemoteClass.setBreakpointMethod Syntax 2: stop at :line number | 0x:line number Uses: RemoteDebugger.findClass or RemoteDebugger.get and RemoteClass.setBreakpointLine This command sets a breakpoint at the first bytecode instruction of the specified method (Syntax 1) or at the first bytecode instruction of the specified line. If Syntax 2 is used, line number is relative to the beginning of the source file that contains /. If stop is issued with no arguments, then the existing breakpoints are displayed. When a breakpoint is placed on a method that is part of a multithreaded.method | 0x.method Uses: RemoteDebugger.findClass or RemoteDebugger.get, RemoteClass.getMethod, and RemoteClass.clearBreakpointMethod Syntax 2: clear :line number | 0x:line number Uses: RemoteDebugger.findClass or RemoteDebugger.get, and RemoteClass.clearBreakpointLine This command clears an existing breakpoint at the first bytecode instruction of the specified method (Syntax 1) or at the first bytecode instruction of the specified line. If Syntax 2 is used, line number is relative to the beginning of the source file that contains /. If clear is issued with no arguments, then the existing breakpoints are displayed. When a breakpoint is cleared from a method that is part of a multithreaded application/applet, then it affects all active threads when they cross that method or line of code. The following example lists the current breakpoints, clears one at the start of MTTest.run, and then displays the breakpoint list again: T0[1] clear Current breakpoints set: MTTest:12 MTTest:10 T0[1] clear MTTest.run Breakpoint cleared at MTTest.run T0[1] clear Current breakpoints set: MTTest:12 T0[1] step Syntax: step Uses: RemoteThread.step This command executes the next instruction of the currently stopped thread. If the next instruction is a method call, execution stops at the first instruction of the method being ]/0x when thrown by the remote JVM. Throwing the exception class causes execution to stop, as if a breakpoint were placed at the first executable statement of the catch block that is currently active when trying the specified exception. In other words, all try-catch blocks in the application that "catch" the specific exception will become breakpoints. If no class is specified, then the existing caught exceptions are displayed. An error is generated if the specified class is not a subclass of Exception. ignore Syntax: ignore ]/0x when thrown by the remote JVM. This does not stop the exception from being thrown, but it does stop the debugger from being able to catch the exception as if it were a breakpoint. If no class is specified, then the existing caught exceptions are displayed. An error is generated if the specified class is not a subclass of Exception.; class... tag. Everything within the <script>... is ignored by Netscape's HTML parser, but is passed on to the JavaScript interpreter. For Web browsers that do not support the <script>... tag, it is customary to further enclose the JavaScript code in comments. Here is an example in Listing 54.1. Listing 54.1 JavaScript Code in an HTML Document JavaScript Hello! <script language="JavaScript">
... to embed this applet in your HTML document. For example, the Java code would appear as: public class HelloWorld extends java.applet.Applet { public static void main (String args []) { System.out.println("Hello World"); } } The HTML code would appear as: Java Example The benefits of having code interpreted by the browser instead of compiled by a compiler and run through the browser is primarily that you—as a JavaScript developer—can very quickly make modifications to your code and test the results via the browser. If you use Java, you must change the code, compile it, upload it again (if you are testing on your own Web server), and then view it in your browser. Interpreted code is typically not as fast as compiled code, but for the limited scope of JavaScript, you will probably see scripts run a little faster than their Java counterparts (with equivalent functions, such as a scrolling text ticker). The drawback to having your JavaScript code on the HTML document is that any code you write will be exposed to anyone else who accesses your page—even those who want to use your code for their own projects. For small scripts, this is not much of a problem, nor is it a problem for large projects—if you don't mind having your efforts used on other pages or improved upon by others. If you have a large project in which you want to keep your code private, you might consider using Java instead. With the recent implementation of the SRC attribute, your scripts can now be pulled out of the HTML page and placed inpass your mouse over here for a message! Instead of showing the URL in the status bar, passing the mouse over the text of the hyperlink brings up a new dialog box that displays the you noticed me! text. To do this in Java, you would have to create an applet that draws the link text to the screen, tag (this pageWelcome! "); alert("Welcome To My Homepage!"); • BODY.JS: document.write("Welcome to my home page!"); The ability to refer to a JavaScript file via the SRC attribute allows you to reuse scripts much more readily than before. It is expected to be only a matter of time before standard libraries of code are developed and easily accessible. It is somewhat ironic that you can find more standard code for Java now than you can for JavaScript, given that Java is more complicated. tag you use when you embed Java code. The SCRIPT tag has an attribute called LANGUAGE that allows you to specify in which language the browser needs to interpret the following code. This makes the <script> tag versatile, in that you may eventually use it to embed Visual Basic Script, TCL, Perl, and more scripts. Another attribute to the <script> tag is SRC. Implemented in Netscape 3.0, the SRC attribute allows you to write all of your script in another file and reference that file— instead of having to paste all of the statements in the HTML. If you use the SRC tag, anything you place between the <script>... is ignored. Thus, you can place alternative HTML for non-JavaScript- enabled browsers. Listing 55.2 uses the SRC attribute. Listing 55.2 JavaScript with SRC <SCRIPT LANGUAGE="JavaScript" SRC="footer.js"> You must not have a JavaScript Enabled Browser if you see this (poor you!) Click here to go to another page. In Listing 55.2, the browser loads the script contained within FOOTER.JS as if it had been typed in the HTML document. Of course, TAG is some HTML tag, and eventHandler is any one of the event handlers you saw in Table 55.1. The "JavaScript code" can be any valid JavaScript code but is usually a call to a function that you loaded earlier in the document. Listing 55.4 demonstrates an embedded JavaScript event handler in a common hypertext link. When you click the link, a dialog box displays the text, followed by an OK button for you to click to return to the page.Click here for a message! There is a lot to notice in this example: • No URL is found in the HREF attribute. Why? You probably don't want the browser to go to another page while the user is viewing the pop-up window. When the user clicks the link, not only is the onClick activated, but the browser attempts to go to the location specified in the HREF. In this case, you are using this link for its onClick event handler and not its hypertext reference. An alternative would be to type: Click here • onClick has mixed case. Although HTML is not case sensitive, JavaScript is. This is important to remember when you are creating functions and variables. • alert(...) is the standard function for bringing up an alert dialog box on the screen. Notice how this function, and all JavaScript functions, behave similarly to Java in that they use parentheses to contain their arguments. In this case, the argument is the string 'Wow! It Works!'. Notice also that the quotation marks of that string are single. When you need to use quotation marks within quotation marks, you nest them by alternating the single and double quotation marks. If you need more than two "levels" of quotations in a given element, you should probably think about an alternate way to eliminate that need. • The JavaScript code in quotation marks—"alert('Wow! It Works!');"—ends in a semicolon. You use the semicolon to end a statement in JavaScript, which is similar to Perl and other languages (including Java). Unlike Perl, the use of the semicolon is optional. Now that you have seen the two main ways you can implement JavaScript in your HTML code (either in scripts contained by the <SCRIPT>... tags or directly embedded in HTML form elements and links), let's look at the building blocks of JavaScript code.Welcome to My Homepage! "); document.write ("The date is " + date + "). ).
