get with the programming Through the power of practice and immediate personalized feedback, MyProgrammingLab improves your performance.
MyProgrammingLab™ Learn more at www.myprogramminglab.com
ALWAYS LEARNING
PEARSON
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INTRODUCTION TO
JAVA TM
PROGRAMMING COMPREHENSIVE VERSION Ninth Edition
Y. Daniel Liang Armstrong Atlantic State University
Boston Columbus Indianapolis New York San Francisco Upper Saddle River Amsterdam Cape Town Dubai London Madrid Milan Munich Paris Montreal Toronto Delhi Mexico City Sao Paulo Sydney Hong Kong Seoul Singapore Taipei Tokyo
Editorial Director: Marcia Horton Editor in Chief: Michael Hirsch Executive Editor: Tracy Dunkelberger Associate Editor: Carole Snyder Director of Marketing: Patrice Jones Marketing Manager: Yez Alayan Marketing Coordinator: Kathryn Ferranti Marketing Assistant: Emma Snider Director of Production: Vince O’Brien Managing Editor: Jeff Holcomb Production Project Manager: Kayla Smith-Tarbox Operations Supervisor: Alan Fischer Manufacturing Buyer: Lisa McDowell
Art Director: Anthony Gemmellaro Cover Designer: Anthony Gemmellaro Manager, Visual Research: Karen Sanatar Manager, Rights and Permissions: Mike Joyce Text Permission Coordinator: Danielle Simon and Jenn Kennett Cover Illustration: Jason Consalvo Lead Media Project Manager: Daniel Sandin Project Management: Gillian Hall Composition and Art: Laserwords Printer/Binder: Edwards Brothers Cover Printer: Lehigh-Phoenix Color/Hagerstown Text Font: Times 10/12
Credits and acknowledgments borrowed from other sources and reproduced, with permission, in this textbook appear on the appropriate page within text and as follows: Table 3.2 and 10.1: Data from IRS. Figures 8.1, 8.12, 12.3, 12.5, 12.7, 12.9, 12.10, 12.12–12.21, 12.26–12.30, 13.1, 13.4, 13.9, 13.11, 13.15, 13.17, 13.19, 13.21, 13.23, 13.25–13.35, 14.10, 14.14,15.9–15.11, 16.1, 16.2, 16.8, 16.11, 16.14, 16.17, 16.19–16.35, 17.1, 17.3, 17.6, 17.9, 17.12, 17.13, 17.15, 17.17–17.32, 18.6–18.8, 18.10, 18.15–18.35, 19.19, 19.20, 19.22, 20.1, 20.9, 20.12–20.14, 20.16–20.20, 22.8, 22.17–22.21, 24.4, 24.6, 24.8, 24.11–24.17, 25.18–25.20, 27.17, 27.23-–27.25, 30.10, 30.14, 30.22, 30.23, 30.25, 31.24–31.26, 32.6, 32.7, 32.31–32.34, 33.5, 33.9–33.11, 33.16–33.22, 34.23, 34.27–34.30: Screenshots © 2011 by Oracle Corporation. Reprinted with permission. Microsoft® and Windows® are registered trademarks of the Microsoft Corporation in the U.S.A. and other countries. Screen shots and icons reprinted with permission from the Microsoft Corporation. This book is not sponsored or endorsed by or affiliated with the Microsoft Corporation.
Copyright © 2013, 2011, 2009, 2007, 2004 by Pearson Education, Inc., publishing as Prentice Hall. All rights reserved. Manufactured in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. To obtain permission(s) to use material from this work, please submit a written request to Pearson Education, Inc., Permissions Department, One Lake Street, Upper Saddle River, New Jersey 07458, or you may fax your request to 201-236-3290. Many of the designations by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed in initial caps or all caps. Library of Congress Cataloging-in-Publication Data available upon request.
10 9 8 7 6 5 4 3 2 1 ISBN 13: 978-0-13-293652-1 ISBN 10: 0-13-293652-6
This book is dedicated to Professor Myers Foreman. Myers used this book in CS1, CS2, and CS3 at Lamar University and provided invaluable suggestions for improving the book. Sadly, Myers passed away after he completed the review of this edition.
To Samantha, Michael, and Michelle
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PREFACE Dear Reader, Many of you have provided feedback on earlier editions of this book, and your comments and suggestions have greatly improved the book. This edition has been substantially enhanced in presentation, organization, examples, exercises, and supplements. We have: ■
Reorganized sections and chapters to present the subjects in a more logical order
■
Included many new interesting examples and exercises to stimulate interests
■
Updated to Java 7
■
Created animations for algorithms and data structures to visually demonstrate the concepts
■
Redesigned the support Website to make it easier to navigate
This book teaches programming in a problem-driven way that focuses on problem solving rather than syntax. We make introductory programming interesting by using thought-provoking problems in a broad context. The central thread of early chapters is on problem solving. Appropriate syntax and library are introduced to enable readers to write programs for solving the problems. To support the teaching of programming in a problem-driven way, the book provides a wide variety of problems at various levels of difficulty to motivate students. To appeal to students in all majors, the problems cover many application areas, including math, science, business, financial, gaming, animation, and multimedia. The book focuses on fundamentals first by introducing basic programming concepts and techniques before designing custom classes. The fundamental concepts and techniques of loops, methods, and arrays are the foundation for programming. Building this strong foundation prepares students to learn object-oriented programming and advanced Java programming. This comprehensive version covers fundamentals of programming, object-oriented programming, GUI programming, algorithms and data structures, concurrency, networking, internationalization, advanced GUI, database, and Web programming. It is designed to prepare students to become proficient Java programmers. A brief version (Introduction to Java Programming, Brief Version, Ninth Edition) is available for a first course on programming, commonly known as CS1. The brief version contains the first 20 chapters of the comprehensive version. The best way to teach programming is by example, and the only way to learn programming is by doing. Basic concepts are explained by example, and a large number of exercises with various levels of difficulty are provided for students to practice. For our programming courses, we assign programming exercises after each lecture. Our goal is to produce a text that teaches problem solving and programming in a broad context using a wide variety of interesting examples. If you have any comments on and suggestions for improving the book, please email me.
what is new?
problem-driven
fundamentals-first
comprehensive version
brief version
examples and exercises
Sincerely, Y. Daniel Liang
[email protected] www.cs.armstrong.edu/liang www.pearsonhighered.com/liang
vii
viii Preface
What’s New in This Edition? This edition substantially improves Introduction to Java Programming, Eighth Edition. The major improvements are as follows: complete revision
■
This edition is completely revised in every detail to enhance clarity, presentation, content, examples, and exercises.
new problems
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New examples and exercises are provided to motivate and stimulate student interest in programming.
key point
■
Each section starts with a Key Point that highlights the important concepts covered in the section.
check point
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Check Points provide review questions to help students track their progress and evaluate their learning after a major concept or example is covered.
test questions
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Each chapter provides test questions online. They are grouped by sections for students to do self-test. The questions are graded online.
VideoNotes
■
New VideoNotes provide short video tutorials designed to reinforce code.
basic GUI and graphics early
■
The Java GUI API is an excellent example of how the object-oriented principle is applied. Students learn better with concrete and visual examples. So basic GUI/Graphics is moved before introducing abstract classes and interfaces. You can however still choose to cover abstract classes and interfaces before GUI or skip GUI.
numeric classes covered early
■
The numeric wrapper classes, BigInteger, and BigDecimal are now introduced in Chapter 10 to enable students to write code using these classes early.
exception handling earlier
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Exception handling is covered before abstract classes and interfaces so that students can build robust programs early. The instructor can still choose to cover exception handling later. Text I/O is now combined with exception handling to form a new chapter.
simple generics early
■
Simple use of generics is introduced along with ArrayList in Chapter 11 and with Comparable in Chapter 15 while the complex detail on generics is still kept in Chapter 21.
splitting Chapter 22
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Chapter 22 is split into two chapters (Chapter 22 and Chapter 23) to make room for incorporating three new case studies to demonstrate effective use of data structures.
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Chapter 24 is expanded to introduce algorithmic techniques: dynamic programming, divide-and-conquer, backtracking, and greedy algorithm with new examples to design efficient algorithms.
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Visual animations are created to show how data structures and algorithms work.
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A common problem with a data structures course is lack of good examples and exercises. This edition added many new interesting examples and exercises.
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Parallel programming techniques are introduced in Chapter 32, Multithreading and Parallel Programming.
new JSF chapter
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Chapter 44 is completely new to introduce the latest standard on JSF.
new JUnit chapter
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Chapter 50 is completely new to introduce testing using JUnit.
developing efficient algorithms data structures and algorithm animation new data structures materials
parallel programming
Please visit www.cs.armstrong.edu/liang/intro9e/newfeatures.html for a complete list of new features as well as correlations to the previous edition.
Preface ix
Pedagogical Features The book uses the following elements to help students get the most from the material: ■
The Objectives at the beginning of each chapter list what students should learn from the chapter. This will help them determine whether they have met the objectives after completing the chapter.
■
The Introduction opens the discussion with representative problems to give the reader an overview of what to expect from the chapter.
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Key Points highlight the important concepts covered in each section.
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Check Points provide review questions to help students track their progress as they read through the chapter and evaluate their learning.
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Problems and Case Studies, carefully chosen and presented in an easy-to-follow style, teach problem solving and programming concepts. The book uses many small, simple, and stimulating examples to demonstrate important ideas.
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The Chapter Summary reviews the important subjects that students should understand and remember. It helps them reinforce the key concepts they have learned in the chapter.
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Test Questions are accessible online, grouped by sections, for students to do self-test on programming concepts and techniques.
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Programming Exercises are grouped by sections to provide students with opportunities to apply the new skills they have learned on their own. The level of difficulty is rated as easy (no asterisk), moderate (*), hard (**), or challenging (***). The trick of learning programming is practice, practice, and practice. To that end, the book provides a great many exercises.
■
Notes, Tips, Cautions, and Design Guides are inserted throughout the text to offer valuable advice and insight on important aspects of program development.
Note Provides additional information on the subject and reinforces important concepts.
Tip Teaches good programming style and practice.
Caution Helps students steer away from the pitfalls of programming errors.
Design Guide Provides guidelines for designing programs.
Flexible Chapter Orderings The book is designed to provide flexible chapter orderings to enable GUI, exception handling, recursion, generics, and the Java Collections Framework to be covered earlier or later. The diagram on the next page shows the chapter dependencies.
Organization of the Book The chapters can be grouped into five parts that, taken together, form a comprehensive introduction to Java programming, data structures and algorithms, and database and Web programming. Because knowledge is cumulative, the early chapters provide the conceptual basis
x Preface
Part I: Fundamentals of Programming
Part III: GUI Programming
Part II: Object-Oriented Programming
Part IV: Data Structures and Algorithms
Chapter 8 Objects and Classes
Chapter 12 GUI Basics
Ch 6
Chapter 20 Recursion
Chapter 9 Strings
Chapter 13 Graphics
Ch 15
Chapter 21 Generics
Chapter 2 Elementary Programming
Chapter 10 Thinking in Objects
Chapter 16 Event-Driven Programming
Chapter 22 Lists, Stacks, Queues, and Priority Queues
Chapter 3 Selections
Chapter 11 Inheritance and Polymorphism
Chapter 17 GUI Components
Chapter 23 Sets and Maps
Chapter 1 Introduction to Computers, Programs, and Java
Ch 18
Part V: Advanced Java Programming Chapter 32 Multithreading and Parallel Programming Chapter 33 Networking Chapter 34 Java Database Programming Chapter 35 Internationalization
Chapter 4 Loops
Chapter 14 Exception Handling and Text I/O
Chapter 18 Applets and Multimedia
Chapter 24 Developping Efficient Algorithms
Chapter 15 Abstract Classes and Interfaces
Chapter 36 JavaBeans and Bean Events
Chapter 25 Sorting
Chapter 5 Methods Chapter 6 Single-Dimensional Arrays
Chapter 19 Binary I/O
Chapter 37 Containers, Layout Managers, and Borders
Chapter 7 Multidimensional Arrays
Chapter 38 Menus, Toolbars, and Dialogs Note: Chapters 1–20 are in the brief version of this book.
Chapter 42 Servlets Chapter 26 Implementing Lists, Stacks, Queues, and Priority Queues Chapter 27 Binary Search Trees Chapter 28 Hashing
Chapter 39 MVC and Swing Models
Note: Chapters 1–34 are in the comprehensive version.
Chapter 29 AVL Trees Chapter 40 JTable and JTree
Note: Chapters 35–50 are bonus chapters available from the Companion Website.
Chapter 49 Java 2D Ch 8
Chapter 50 Testing Using JUnit
Chapter 41 Advanced Database Programming
Chapter 30 Graphs and Applications Chapter 31 Weighted Graphs and Applications Chapter 47 2-4 Trees and BTrees Chapter 48 Red-Black Trees
Chapter 43 Java Server Pages Chapter 44 Java Server Faces Chapter 45 Web Services Chapter 46 Remote Method Invocation
Preface xi for understanding programming and guide students through simple examples and exercises; subsequent chapters progressively present Java programming in detail, culminating with the development of comprehensive Java applications. The appendixes contain a mixed bag of topics, including an introduction to number systems and bitwise operations. Part I: Fundamentals of Programming (Chapters 1–7) The first part of the book is a stepping stone, preparing you to embark on the journey of learning Java. You will begin to learn about Java (Chapter 1) and fundamental programming techniques with primitive data types, variables, constants, assignments, expressions, and operators (Chapter 2), control statements (Chapters 3–4), methods (Chapter 5), and arrays (Chapters 6–7). After Chapter 6, you can jump to Chapter 20 to learn how to write recursive methods for solving inherently recursive problems. Part II: Object-Oriented Programming (Chapters 8–11, 14–15, and 19) This part introduces object-oriented programming. Java is an object-oriented programming language that uses abstraction, encapsulation, inheritance, and polymorphism to provide great flexibility, modularity, and reusability in developing software. You will learn programming with objects and classes (Chapters 8–10), class inheritance (Chapter 11), polymorphism (Chapter 11), exception handling and text I/O (Chapter 14), abstract classes (Chapter 15), and interfaces (Chapter 15). Processing strings is introduced in Chapter 9, and binary I/O is discussed in Chapter 19. Part III: GUI Programming (Chapters 12–13, 16–18, and Bonus Chapters 36–40 and 49) This part introduces elementary Java GUI programming in Chapters 12–13 and 16–18 and advanced Java GUI programming in Chapters 36–40 and 49. Major topics include GUI basics (Chapter 12), drawing shapes (Chapter 13), event-driven programming (Chapter 16), using GUI components (Chapter 17), and writing applets (Chapter 18). You will learn the architecture of Java GUI programming and use the GUI components to develop applications and applets from these elementary GUI chapters. The advanced GUI chapters discuss Java GUI programming in more depth and breadth. You will delve into JavaBeans and learn how to develop custom events and source components in Chapter 36, review and explore new containers, layout managers, and borders in Chapter 37, learn how to create GUI with menus, popup menus, toolbars, dialogs, and internal frames in Chapter 38, develop components using the MVC approach and explore the advanced Swing components JSpinner, JList, and JComboBox in Chapter 39, and JTable and JTree in Chapter 40. Chapter 49 introduces Java 2D. Part IV: Data Structures and Algorithms (Chapters 20–31 and Bonus Chapters 47–48) This part covers the main subjects in a typical data structures course. Chapter 20 introduces recursion to write methods for solving inherently recursive problems. Chapter 21 presents how generics can improve software reliability. Chapters 22 and 23 introduce the Java Collection Framework, which defines a set of useful API for data structures. Chapter 24 discusses measuring algorithm efficiency in order to choose an appropriate algorithm for applications. Chapter 25 describes classic sorting algorithms. You will learn how to implement several classic data structures lists, queues, and priority queues in Chapter 26. Chapters 27 and 29 introduce binary search trees and AVL trees. Chapter 28 presents hashing and implementing maps and sets using hashing. Chapters 30 and 31 introduce graph applications. The 2-4 trees, B-trees, and red-black trees are covered in Chapters 47–48. Part V: Advanced Java Programming (Chapters 32–33 and Bonus Chapters 35, 41–46, and 50) This part of the book is devoted to advanced Java programming. Chapter 32 treats the use of multithreading to make programs more responsive and interactive and introduces parallel programming. Chapter 33 discusses how to write programs that talk with each other
xii Preface over the Internet. Chapter 34 introduces the use of Java to develop database projects, and Chapter 35 covers the use of internationalization support to develop projects for international audiences. Chapter 41 delves into advanced Java database programming. Bonus Chapters 42, 43 and 44 introduce how to use Java servlets, JavaServer Pages, and JavaServer Faces to generate dynamic content from Web servers. Chapter 45 discusses Web services, and Chapter 46 introduces remote method invocation. Chapter 50 introduces testing Java programs using JUnit. Appendixes This part of the book covers a mixed bag of topics. Appendix A lists Java keywords. Appendix B gives tables of ASCII characters and their associated codes in decimal and in hex. Appendix C shows the operator precedence. Appendix D summarizes Java modifiers and their usage. Appendix E discusses special floating-point values. Appendix F introduces number systems and conversions among binary, decimal, and hex numbers. Finally, Appendix G introduces bitwise operations.
Java Development Tools You can use a text editor, such as the Windows Notepad or WordPad, to create Java programs and to compile and run the programs from the command window. You can also use a Java development tool, such as TextPad, NetBeans, or Eclipse. These tools support an integrated development environment (IDE) for developing Java programs quickly. Editing, compiling, building, executing, and debugging programs are integrated in one graphical user interface. Using these tools effectively can greatly increase your programming productivity. TextPad is a primitive IDE tool. NetBeans and Eclipse are more sophisticated, but they are easy to use if you follow the tutorials. Tutorials on TextPad, NetBeans, and Eclipse can be found in the supplements on the Companion Website www.cs.armstrong.edu/liang/intro9e.
IDE tutorials
Online Practice and Assessment with MyProgrammingLab MyProgrammingLab helps students fully grasp the logic, semantics, and syntax of programming. Through practice exercises and immediate, personalized feedback, MyProgrammingLab improves the programming competence of beginning students who often struggle with the basic concepts and paradigms of popular high-level programming languages. A self-study and homework tool, a MyProgrammingLab course consists of hundreds of small practice problems organized around the structure of this textbook. For students, the system automatically detects errors in the logic and syntax of their code submissions and offers targeted hints that enable students to figure out what went wrong—and why. For instructors, a comprehensive gradebook tracks correct and incorrect answers and stores the code inputted by students for review. MyProgrammingLab is offered to users of this book in partnership with Turing’s Craft, the makers of the CodeLab interactive programming exercise system. For a full demonstration, to see feedback from instructors and students, or to get started using MyProgrammingLab in your course, visit www.myprogramminglab.com.
VideoNotes VideoNote
We are excited about the new VideoNotes feature that is found in this new edition. These videos provide additional help by presenting examples of key topics and showing how to solve problems completely, from design through coding. VideoNotes are free to first time users and can be accessed by redeeming the access code in the front of this book at www.pearsonhighered.com/liang.
Preface xiii
LiveLab This book is accompanied by a complementary Web-based course assessment and management system for instructors. The system has four main components: ■
The Automatic Grading System can automatically grade programs.
■
The Quiz Creation/Submission/Grading System enables instructors to create and modify quizzes that students can take and be graded upon automatically.
■
The Peer Evaluation System enables peer evaluations.
■
Tracking grades, attendance, etc., lets students track their grades, and enables instructors to view the grades of all students and to track students’ attendance.
The main features of the Automatic Grading System include: ■
Students can run and submit exercises. (The system checks whether their program runs correctly—students can continue to run and resubmit the program before the due date.)
■
Instructors can review submissions, run programs with instructor test cases, correct them, provide feedback to students, and check plagiarism.
■
Instructors can create/modify their own exercises, create public and secret test cases, assign exercises, and set due dates for the whole class or for individuals.
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Instructors can assign all the exercises in the text to students. Additionally, LiveLab provides extra exercises that are not printed in the text.
■
Instructors can sort and filter all exercises and check grades (by time frame, student, and/or exercise).
■
Instructors can delete students from the system.
■
Students and instructors can track grades on exercises.
The main features of the Quiz System are: ■
Instructors can create/modify quizzes from the test bank or a text file or create completely new tests online.
■
Instructors can assign the quizzes to students and set a due date and test time limit for the whole class or for individuals.
■
Students and instructors can review submitted quizzes.
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Instructors can analyze quizzes and identify students’ weaknesses.
■
Students and instructors can track grades on quizzes.
The main features of the Peer Evaluation System include: ■
Instructors can assign peer evaluation for programming exercises.
■
Instructors can view peer evaluation reports.
Student Resource Website The Student Resource Website (www.cs.armstrong.edu/liang/intro9e) contains the following resources: ■
Access to VideoNotes (www.pearsonhighered.com/liang).
■
Answers to check point questions
xiv Preface ■
Solutions to even-numbered programming exercises
■
Source code for the examples in the book
■
Interactive self-testing (organized by sections for each chapter)
■
Data structures and algorithm animations
■
Errata
Instructor Resource Website The Instructor Resource Website, accessible from www.cs.armstrong.edu/liang/intro9e, contains the following resources: ■
Microsoft PowerPoint slides with interactive buttons to view full-color, syntax-highlighted source code and to run programs without leaving the slides.
■
Solutions to all programming exercises. Students will have access to the solutions of evennumbered programming exercises.
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Web-based quiz generator. (Instructors can choose chapters to generate quizzes from a large database of more than two thousand questions.)
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Sample exams. Most exams have four parts:
■
■
Multiple-choice questions or short-answer questions
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Correct programming errors
■
Trace programs
■
Write programs
Projects. In general, each project gives a description and asks students to analyze, design, and implement the project.
Some readers have requested the materials from the Instructor Resource Website. Please understand that these are for instructors only. Such requests will not be answered.
Algorithm Animations We have provided numerous animations for algorithms. These are valuable pedagogical tools to demonstrate how algorithms work. Algorithm animations can be accessed from the Companion Website.
Acknowledgments I would like to thank Armstrong Atlantic State University for enabling me to teach what I write and for supporting me in writing what I teach. Teaching is the source of inspiration for continuing to improve the book. I am grateful to the instructors and students who have offered comments, suggestions, bug reports, and praise. This book has been greatly enhanced thanks to outstanding reviews for this and previous editions. The reviewers are: Elizabeth Adams (James Madison University), Syed Ahmed (North Georgia College and State University), Omar Aldawud (Illinois Institute of Technology), Yang Ang (University of Wollongong, Australia), Kevin Bierre (Rochester Institute of Technology), David Champion (DeVry Institute), James Chegwidden (Tarrant County College), Anup Dargar (University of North Dakota), Charles Dierbach (Towson University), Frank Ducrest (University of Louisiana at Lafayette), Erica Eddy (University of Wisconsin at Parkside), Deena
Preface xv Engel (New York University), Henry A. Etlinger (Rochester Institute of Technology), James Ten Eyck (Marist College), Myers Foreman (Lamar University), Olac Fuentes (University of Texas at El Paso), Edward F. Gehringer (North Carolina State University), Harold Grossman (Clemson University), Barbara Guillot (Louisiana State University), Stuart Hansen (University of Wisconsin, Parkside), Dan Harvey (Southern Oregon University), Ron Hofman (Red River College, Canada), Stephen Hughes (Roanoke College), Vladan Jovanovic (Georgia Southern University), Edwin Kay (Lehigh University), Larry King (University of Texas at Dallas), Nana Kofi (Langara College, Canada), George Koutsogiannakis (Illinois Institute of Technology), Roger Kraft (Purdue University at Calumet), Norman Krumpe (Miami University), Hong Lin (DeVry Institute), Dan Lipsa (Armstrong Atlantic State University), James Madison (Rensselaer Polytechnic Institute), Frank Malinowski (Darton College), Tim Margush (University of Akron), Debbie Masada (Sun Microsystems), Blayne Mayfield (Oklahoma State University), John McGrath (J.P. McGrath Consulting), Hugh McGuire (Grand Valley State), Shyamal Mitra (University of Texas at Austin), Michel Mitri (James Madison University), Kenrick Mock (University of Alaska Anchorage), Frank Murgolo (California State University, Long Beach), Jun Ni (University of Iowa), Benjamin Nystuen (University of Colorado at Colorado Springs), Maureen Opkins (CA State University, Long Beach), Gavin Osborne (University of Saskatchewan), Kevin Parker (Idaho State University), Dale Parson (Kutztown University), Mark Pendergast (Florida Gulf Coast University), Richard Povinelli (Marquette University), Roger Priebe (University of Texas at Austin), Mary Ann Pumphrey (De Anza Junior College), Pat Roth (Southern Polytechnic State University), Amr Sabry (Indiana University), Carolyn Schauble (Colorado State University), David Scuse (University of Manitoba), Ashraf Shirani (San Jose State University), Daniel Spiegel (Kutztown University), Joslyn A. Smith (Florida Atlantic University) , Lixin Tao (Pace University), Ronald F. Taylor (Wright State University), Russ Tront (Simon Fraser University), Deborah Trytten (University of Oklahoma), Kent Vidrine (George Washington University), and Bahram Zartoshty (California State University at Northridge). It is a great pleasure, honor, and privilege to work with Pearson. I would like to thank Tracy Dunkelberger and her colleagues Marcia Horton, Michael Hirsch, Matt Goldstein, Carole Snyder, Tim Huddleston, Yez Alayan, Jeff Holcomb, Kayla Smith-Tarbox, Gillian Hall, Rebecca Greenberg, and their colleagues for organizing, producing, and promoting this project. As always, I am indebted to my wife, Samantha, for her love, support, and encouragement.
BRIEF CONTENTS 1 Introduction to Computers, Programs, 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 xvi
and Java Elementary Programming Selections Loops Methods Single-Dimensional Arrays Multidimensional Arrays Objects and Classes Strings Thinking in Objects Inheritance and Polymorphism GUI Basics Graphics Exception Handling and Text I/O Abstract Classes and Interfaces Event-Driven Programming GUI Components Applets and Multimedia Binary I/O Recursion Generics Lists, Stacks, Queues, and Priority Queues Sets and Maps Developing Efficient Algorithms Sorting Implementing Lists, Stacks, Queues, and Priority Queues Binary Search Trees Hashing AVL Trees Graphs and Applications Weighted Graphs and Applications Multithreading and Parallel Programming
1 33 81 133 177 223 263 295 335 369 407 445 479 517 559 599 639 671 709 737 769 793 829 853 893 927 961 997 1027 1047 1093 1129
33 Networking 34 Java Database Programming
1175 1211
Chapters 35–50 are bonus Web chapters 35 Internationalization 36 JavaBeans 37 Containers, Layout Managers, 38 39 40 41 42 43 44 45 46 47 48 49 50
and Borders Menus, Toolbars, and Dialogs MVC and Swing Models JTable and JTree Advanced Database Programming Servlets JavaServer Pages JavaServer Faces Web Services Remote Method Invocation 2-4 Trees and B-Trees Red-Black Trees Java 2D Testing Using JUnit
35-1 36-1 37-1 38-1 39-1 40-1 41-1 42-1 43-1 44-1 45-1 46-1 47-1 48-1 49-1 50-1
APPENDIXES A B C D E F G
Java Keywords The ASCII Character Set Operator Precedence Chart Java Modifiers Special Floating-Point Values Number Systems Bitwise Operatoirns
INDEX
1251 1254 1256 1258 1260 1261 1265
1267
CONTENTS Chapter 1 Introduction to Computers, Programs, and Java 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11
Introduction What Is a Computer? Programming Languages Operating Systems Java, the World Wide Web, and Beyond The Java Language Specification, API, JDK, and IDE A Simple Java Program Creating, Compiling, and Executing a Java Program Displaying Text in a Message Dialog Box Programming Style and Documentation Programming Errors
Chapter 2 Elementary Programming 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19
Introduction Writing a Simple Program Reading Input from the Console Identifiers Variables Assignment Statements and Assignment Expressions Named Constants Naming Conventions Numeric Data Types and Operations Numeric Literals Evaluating Expressions and Operator Precedence Case Study: Displaying the Current Time Augmented Assignment Operators Increment and Decrement Operators Numeric Type Conversions Software Development Process Character Data Type and Operations The String Type Getting Input from Input Dialogs
Chapter 3 Selections 3.1 3.2
Introduction boolean Data Type
1 2 2 9 12 13 16 16 19 22 24 26 33 34 34 37 40 40 42 43 44 44 48 50 51 53 54 56 58 62 68 70 81 82 82
xvii
xviii Contents 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19
if Statements
Case Study: Guessing Birthdays Two-Way if-else Statements Nested if and Multi-Way if-else Statements Common Errors in Selection Statements Generating Random Numbers Case Study: Computing Body Mass Index Case Study: Computing Taxes Logical Operators Case Study: Determining Leap Year Case Study: Lottery switch Statements Conditional Expressions Formatting Console Output Operator Precedence and Associativity Confirmation Dialogs Debugging
84 86 89 91 93 96 97 99 101 105 106 108 111 112 115 117 119
Chapter 4 Loops
133
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11
134 134 144 146 150 152 154 155 159 162 164
Introduction The while Loop The do-while Loop The for Loop Which Loop to Use? Nested Loops Minimizing Numeric Errors Case Studies Keywords break and continue Case Study: Displaying Prime Numbers Controlling a Loop with a Confirmation Dialog
Chapter 5 Methods 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10
177
Introduction Defining a Method Calling a Method
178 178 180
void Method Example
183 186 189 191 193 196
Passing Parameters by Values Modularizing Code Case Study: Converting Decimals to Hexadecimals Overloading Methods The Scope of Variables The Math Class
197
Contents xix 5.11 5.12
Case Study: Generating Random Characters Method Abstraction and Stepwise Refinement
Chapter 6 Single-Dimensional Arrays 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12
Introduction Array Basics Case Study: Lotto Numbers Case Study: Deck of Cards Copying Arrays Passing Arrays to Methods Returning an Array from a Method Case Study: Counting the Occurrences of Each Letter Variable-Length Argument Lists Searching Arrays Sorting Arrays The Arrays Class
Chapter 7 Multidimensional Arrays 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8
Introduction Two-Dimensional Array Basics Processing Two-Dimensional Arrays Passing Two-Dimensional Arrays to Methods Case Study: Grading a Multiple-Choice Test Case Study: Finding the Closest Pair Case Study: Sudoku Multidimensional Arrays
Chapter 8 Objects and Classes 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11
Introduction Defining Classes for Objects Example: Defining Classes and Creating Objects Constructing Objects Using Constructors Accessing Objects via Reference Variables Using Classes from the Java Library Static Variables, Constants, and Methods Visibility Modifiers Data Field Encapsulation Passing Objects to Methods Array of Objects
Chapter 9 Strings 9.1 9.2
Introduction The String Class
201 203 223 224 224 231 234 236 237 240 241 244 245 248 252 263 264 264 267 269 270 272 274 277 295 296 296 298 303 304 308 312 317 319 322 326 335 336 336
xx Contents 9.3 9.4 9.5 9.6
Case Study: Checking Palindromes Case Study: Converting Hexadecimals to Decimals The Character Class The StringBuilder and StringBuffer
9.7
Command-Line Arguments
Chapter 10 Thinking in Objects 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 10.11 10.12 10.13 10.14
Introduction Immutable Objects and Classes The Scope of Variables The this Reference Class Abstraction and Encapsulation Object-Oriented Thinking Object Composition Case Study: Designing the Course Class Case Study: Designing a Class for Stacks Case Study: Designing the GuessDate Class Class Design Guidelines Processing Primitive Data Type Values as Objects Automatic Conversion between Primitive Types and Wrapper Class Types The BigInteger and BigDecimal
Chapter 11 Inheritance and Polymorphism 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 11.10 11.11 11.12 11.13
Introduction Superclasses and Subclasses Using the super Keyword Overriding Methods Overriding vs. Overloading The Object Class and Its toString() Polymorphism Dynamic Binding Casting Objects and the instanceof Operator The Object’s equals method The ArrayList Class Case Study: A Custom Stack Class The protected Data and Methods
11.14
Preventing Extending and Overriding
Chapter 12 GUI Basics 12.1 12.2
Introduction Swing vs. AWT
347 348 350 353 358 369 370 370 371 373 375 379 382 384 386 388 391 393 396 397 407 408 408 414 418 418 420 421 422 425 429 430 436 437 439 445 446 446
Contents xxi 12.3 12.4 12.5 12.6 12.7 12.8 12.9 12.10 12.11 12.12 12.13 12.14 12.15
The Java GUI API Frames Layout Managers Using Panels as Subcontainers The Color Class The Font Class Common Features of Swing GUI Components Image Icons JButton JCheckBox JRadioButton
Labels Text Fields
Chapter 13 Graphics 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.11
Introduction The Graphics Class Drawing Strings, Lines, Rectangles, and Ovals Case Study: The FigurePanel Class Drawing Arcs Drawing Polygons and Polylines Centering a String Using the FontMetrics Class Case Study: The MessagePanel Class Case Study: The StillClock Class Displaying Images Case Study: The ImageViewer Class
Chapter 14 Exception Handling and Text I/O 14.1 14.2 14.3 14.4 14.5 14.6 14.7 14.8 14.9 14.10
Introduction Exception-Handling Overview Exception Types More on Exception Handling The finally Clause When to Use Exceptions Rethrowing Exceptions Chained Exceptions Defining Custom Exception Classes The File Class
14.11 14.12 14.13
File Input and Output File Dialogs Reading Data from the Web
446 449 451 458 460 461 462 465 467 471 472 473 474
479 480 480 483 485 488 490 493 495 500 504 506
517 518 518 523 526 534 535 536 537 538 541 544 549 551
xxii Contents
Chapter 15 Abstract Classes and Interfaces
559
15.1 15.2
Introduction Abstract Classes
560 560
15.3 15.4 15.5 15.6 15.7
Case Study: the Abstract Number Class Case Study: Calendar and GregorianCalendar Interfaces The Comparable Interface The Cloneable Interface
565 567 570 573 577
15.8 15.9
Interfaces vs. Abstract Classes Case Study: The Rational Class
581 584
Chapter 16 Event-Driven Programming
599
16.1 16.2
Introduction Events and Event Sources
600 602
16.3 16.4
Listeners, Registrations, and Handling Events Inner Classes
603 608
16.5 16.6 16.7
Anonymous Class Listeners Alternative Ways of Defining Listener Classes Case Study: Loan Calculator
609 612 615
Mouse Events Listener Interface Adapters Key Events Animation Using the Timer Class
617 620 621 625
16.8 16.9 16.10 16.11
Chapter 17 GUI Components
639
17.1 17.2 17.3 17.4 17.5
Introduction Events for JCheckBox, JRadioButton and JTextField Text Areas Combo Boxes Lists
640 640 644 647 650
17.6 17.7 17.8
Scroll Bars Sliders Creating Multiple Windows
654 657 660
Chapter 18 Applets and Multimedia
671
18.1 18.2
Introduction Developing Applets
672 672
18.3 18.4
The HTML File and the
Tag Applet Security Restrictions 5 invokevirtual #4 … 8 returncb?a Ignoring nonalphanumeric characters, is abcb?a a palindrome? true cities = new ArrayList(); dates = new ArrayList (); list = new ArrayList (); list = new ArrayList<> (); cityList = new ArrayList(); // Add some cities in the list cityList.add("London"); // cityList now contains [London] cityList.add("Denver"); // cityList now contains [London, Denver] cityList.add("Paris"); // cityList now contains [London, Denver, Paris] cityList.add("Miami"); // cityList now contains [London, Denver, Paris, Miami] cityList.add("Seoul"); // Contains [London, Denver, Paris, Miami, Seoul] cityList.add("Tokyo"); // Contains [London, Denver, Paris, Miami, Seoul, Tokyo] System.out.println("List size? " + cityList.size() ); System.out.println("Is Miami in the list? " + cityList.contains("Miami") ); System.out.println("The location of Denver in the list? " + cityList.indexOf("Denver") ); System.out.println("Is the list empty? " + cityList.isEmpty() ); // Print false // Insert a new city at index 2 cityList.add(2, "Xian"); // Contains [London, Denver, Xian, Paris, Miami, Seoul, Tokyo] // Remove a city from the list cityList.remove("Miami"); // Contains [London, Denver, Xian, Paris, Seoul, Tokyo] // Remove a city at index 1 cityList.remove(1); // Contains [London, Xian, Paris, Seoul, Tokyo] // Display the contents in the list System.out.println(cityList.toString()); // Display the contents in the list in reverse order for (int i = cityList.size() - 1; i >= 0; i– –) System.out.print(cityList.get(i) + " "); System.out.println(); // Create a list to store two circles ArrayList list = new ArrayList(); // Add two circles list.add(new CircleFromSimpleGeometricObject(2)); list.add(new CircleFromSimpleGeometricObject(3)); // Display the area of the first circle in the list System.out.println("The area of the circle? " + ((CircleFromSimpleGeometricObject)list.get(0)).getArea()); } } list = new ArrayList<>(); list = new ArrayList(); list = new ArrayList(); list = new ArrayList(); Scanner input = new Scanner(System.in); System.out.print("Enter integers (input ends with 0): "); int value; do { value = input.nextInt(); // Read a value from the input if (!list.contains(value) && value != 0) list.add(value); // Add the value if it is not in the list } while (value != 0); list = new ArrayList (); list.add("Denver"); list.add("Austin"); list.add(new java.util.Date()); String city = list.get(0); list.set(3, "Dallas"); System.out.println(list.get(3)); list = new ArrayList(); list.add(1); list = new ArrayList(); public boolean isEmpty() { return list.isEmpty(); } public int getSize() { return list.size(); } public Object peek() { return list.get(getSize() - 1); } public Object pop() { Object o = list.get(getSize() - 1); list.remove(getSize() - 1); return o; } public void push(Object o) { list.add(o); } list) list) list) list) list = new ArrayList(); list.add(45); // Add an integer list.add(3445.53); // Add a double // Add a BigInteger list.add(new BigInteger("3432323234344343101")); // Add a BigDecimal list.add(new BigDecimal("2.0909090989091343433344343")); System.out.println("The largest number is " + getLargestNumber(list)); } public static Number getLargestNumber(ArrayList list) { if (list == null || list.size() == 0) return null; Number number = list.get(0); for (int i = 1; i < list.size(); i++) if (number.doubleValue() < list.get(i).doubleValue()) number = list.get(i); return number; } } { public int compareTo(E o); } { // class body omitted { // class body omitted { // class body omitted // class body omitted { /** Construct a ComparableRectangle with specified properties */ public ComparableRectangle(double width, double height) { super(width, height); } @Override // Implement the compareTo method defined in Comparable public int compareTo(ComparableRectangle o) { if (getArea() > o.getArea()) return 1; else if (getArea() < o.getArea()) return -1; else return 0; } @Override // Implement the toString method in GeometricObject public String toString() { return super.toString() + " Area: " + getArea(); } } +compareTo(o: ComparableRectangle): int list1 = list1.add(1.5); list1.add(2.5); list1.add(3.5); ArrayList list2 = ArrayList list3 = list2.add(4.5); list3.remove(1.5); System.out.println("list1 System.out.println("list2 System.out.println("list3();)list1.clone(); list1; { private int id; private double area; private java.util.Date whenBuilt; public House(int id, double area) { this.id = id; this.area = area; whenBuilt = new java.util.Date(); } public int getId() { list = new ArrayList(); list.add("New York"); ArrayList list1 = list; ArrayList list2 = (ArrayList)(list.clone()); list.add("Atlanta"); System.out.println(list == list1); System.out.println(list == list2); System.out.println("list is " + list); System.out.println("list1 is " + list1); System.out.println("list2.get(0) is " + list2.get(0)); System.out.println("list2.size() is " + list2.size()); { // Data fields for numerator and denominator private long numerator = 0; private long denominator = 1; /** Construct a rational with default properties */ public Rational() { this(0, 1); } /** Construct a rational with specified numerator and denominator */ public Rational(long numerator, long denominator) { long gcd = gcd(numerator, denominator); this.numerator = ((denominator > 0) ? 1 : -1) * numerator / gcd; this.denominator = Math.abs(denominator) / gcd; } /** Find GCD of two numbers */ private static long gcd(long n, long d) { long n1 = Math.abs(n); long n2 = Math.abs(d); int gcd = 1; list) list)(). In the JSlider class, the get methods for Tag 673 4 5 6 7 Tag To run an applet, you need to create an HTML file with an tag for embedding the applet. HTML is a markup language that presents static documents on the Web. It uses tags to instruct the Web browser how to render a Web page and contains a tag called that incorporates applets into a Web page. The HTML file in Listing 18.2 embeds the applet DisplayLabel.class.Java Applet Demo is the tag name, and code, width, and height are attributes. The width and height attributes specify the rectangular viewing area of the applet. Most tags have a start tag and a corresponding end tag. The tag has a specific effect on the region between the start tag and the end tag. For example, ... tells the browser to display an applet. An end tag is always the start tag’s name preceded by a slash. An HTML document begins with the tag, which declares that the document is written in HTML. Each document has two parts, a head and a body, defined by and tags, respectively. The head part contains the document title, including the tag and other information the browser can use when rendering the document, and the body part holds the actual contents of the document. The header is optional. For more information, refer to Supplement V.A, HTML and XHTML Tutorial. The complete syntax of the <applet rel="nofollow"> tag is as follows: <applet [codebase = applet_url]<br / rel="nofollow">
<br />
applet class<br />
<br />
tag<br />
<br />
<applet rel="nofollow"> tag<br />
<br />
674 Chapter 18<br />
<br />
Applets and Multimedia code = classfilename.class width = applet_viewing_width_in_pixels height = applet_viewing_height_in_pixels [archive = archivefile] [vspace = vertical_margin] [hspace = horizontal_margin] [align = applet_alignment] [alt = alternative_text] > <param name = param_name1 value = param_value1> <param name = param_name2 value = param_value2> ... <param name = param_namei value = param_valuei> </applet><br />
<br />
<param> tag<br />
<br />
The code, width, and height attributes are required; all the others are optional. The <param> tag will be introduced in Section 18.7, Passing Strings to Applets. The other attributes are explained below. codebase attribute<br />
<br />
■ codebase<br />
<br />
archive attribute<br />
<br />
■ archive<br />
<br />
specifies the base from which your classes are loaded. If this attribute is not used, the Web browser loads the applet from the directory in which the HTML page is located. If your applet is located in a different directory from the HTML page, you must specify the applet_url for the browser to load the applet. This attribute enables you to load the class from anywhere on the Internet. The classes used by the applet are dynamically loaded when needed. instructs the browser to load an archive file that contains all the class files needed to run the applet. Archiving allows the Web browser to load all the classes from a single compressed file at one time, thus reducing loading time and improving performance. To create archives, see Supplement III.Q, Packaging and Deploying Java Projects.<br />
<br />
■ vspace<br />
<br />
and hspace specify the size, in pixels, of the blank margin to pad around the applet vertically and horizontally.<br />
<br />
■ align<br />
<br />
specifies how the applet will be aligned in the browser. One of nine values is used: left, right, top, texttop, middle, absmiddle, baseline, bottom, or absbottom.<br />
<br />
■ alt<br />
<br />
specifies the text to be displayed in case the browser cannot run Java.<br />
<br />
18.3.1 Viewing Applets from a Web Browser To display an applet from a Web browser, open the applet’s HTML file (e.g., DisplayLabel.html). Its output is shown in Figure 18.2a. To make your applet accessible on the Web, you need to store the DisplayLabel.class and DisplayLabel.html files on a Web server, as shown in Figure 18.3. You can view the applet<br />
<br />
(a)<br />
<br />
FIGURE 18.2<br />
<br />
(b)<br />
<br />
The DisplayLabel program is loaded from a local host in (a) and from a Web server in (b).<br />
<br />
18.4 Applet Security Restrictions 675 http://www.webserver.com/appropriatepath/DisplayLabel.html<br />
<br />
Web Browser HTML Page<br />
<br />
FIGURE 18.3<br />
<br />
Web Server The .html file and applet’s .class files are stored on the Web server.<br />
<br />
A Web browser requests an HTML file from a Web server.<br />
<br />
from an appropriate URL. For example, I have uploaded these two files on Web server www.cs.armstrong.edu/. As shown in Figure 18.2b, you can access the applet from www.cs.armstrong.edu/liang/intro9e/book/DisplayLabel.html.<br />
<br />
18.3.2<br />
<br />
Viewing Applets Using the Applet Viewer Utility<br />
<br />
You can test the applet using the applet viewer utility, which can be launched from the DOS prompt using the appletviewer command, as shown in Figure 18.4a. Its output is shown in Figure 18.4b.<br />
<br />
(a)<br />
<br />
FIGURE 18.4<br />
<br />
appletviewer<br />
<br />
(b)<br />
<br />
The appletviewer command runs a Java applet in the applet viewer utility.<br />
<br />
The applet viewer functions as a browser. It is convenient for testing applets during development without launching a Web browser.<br />
<br />
18.3 Describe the <applet rel="nofollow"> HTML tag. How do you embed an applet in a web page? 18.4 How do you test an applet using the appletviewer command?<br />
<br />
✓<br />
<br />
Check Point<br />
<br />
18.4 Applet Security Restrictions Applet security restrictions ensure that safety is maintained when running applets. Java uses the so-called “sandbox security model” for executing applets to prevent destructive programs from damaging the system on which the browser is running. Applets are not allowed to use resources outside the “sandbox.” Specifically, the sandbox restricts the following activities: ■<br />
<br />
Applets are not allowed to read from, or write to, the file system of the computer. Otherwise, they could damage the files and spread viruses.<br />
<br />
■<br />
<br />
Applets are not allowed to run programs on the browser’s computer. Otherwise, they might call destructive local programs and damage the local system on the user’s computer.<br />
<br />
■<br />
<br />
Applets are not allowed to establish connections between the user’s computer and any other computer, except for the server where the applets are stored. This restriction prevents the applet from connecting the user’s computer to another computer without the user’s knowledge.<br />
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Key Point<br />
<br />
676 Chapter 18<br />
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Applets and Multimedia Note You can create signed applets to circumvent the security restrictions. See Supplement III.S, Signed Applets, for detailed instructions on how to create signed applets.<br />
<br />
signed applet<br />
<br />
✓<br />
<br />
Check Point<br />
<br />
Key Point<br />
<br />
VideoNote<br />
<br />
Run applets standalone<br />
<br />
18.5<br />
<br />
List some security restrictions on applets.<br />
<br />
18.5 Enabling Applets to Run as Applications You can add a main method in the applet to enable the applet to run as a standalone application. Despite some differences, the JFrame class and the JApplet class have a lot in common. Since they both are subclasses of the Container class, all their user-interface components, layout managers, and event-handling features are the same. Applications, however, are invoked from the static main method by the Java interpreter, and applets are run by the Web browser. The Web browser creates an instance of the applet using the applet’s no-arg constructor and controls and executes the applet. In general, an applet can be converted into an application without loss of functionality. An application can be converted into an applet as long as it does not violate the security restrictions imposed on applets. You can implement a main method in an applet to enable the applet to run as an application. This feature has both theoretical and practical implications. Theoretically, it blurs the difference between applets and applications: You can write a class that is both an applet and an application. From the standpoint of practicality, it is convenient to be able to run a program both ways. How do you write such programs? Suppose you have an applet named MyApplet. To enable it to run as an application, you only need to add a main method in the applet, as follows: public static void main(String[] args) { // Create a frame JFrame frame = new JFrame("Applet is in the frame");<br />
<br />
create frame<br />
<br />
create applet<br />
<br />
// Create an instance of the applet MyApplet applet = new MyApplet();<br />
<br />
add applet<br />
<br />
// Add the applet to the frame frame.add(applet, BorderLayout.CENTER);<br />
<br />
show frame<br />
<br />
// Display the frame frame.setSize(300, 300); frame.setLocationRelativeTo(null); // Center the frame frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); }<br />
<br />
run standalone<br />
<br />
You can revise the DisplayLabel class in Listing 18.1 to enable it to run as a standalone application (often abbreviated as “run standalone”) by adding a main method, as shown in Listing 18.3.<br />
<br />
LISTING 18.3 New DisplayLabel.java with a main Method 1 2 3 4 5 6 7<br />
<br />
import javax.swing.*; public class DisplayLabel extends JApplet { public DisplayLabel() { add(new JLabel("Great!", JLabel.CENTER)); }<br />
<br />
18.6 Applet Life-Cycle Methods 677 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24<br />
<br />
public static void main(String[] args) { // Create a frame JFrame frame = new JFrame("Applet is in the frame");<br />
<br />
new main method<br />
<br />
// Create an instance of the applet DisplayLabel applet = new DisplayLabel(); // Add the applet to the frame frame.add(applet); // Display the frame frame.setSize(300, 100); frame.setLocationRelativeTo(null); // Center the frame frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); } }<br />
<br />
When the applet is run from a Web browser, the browser creates an instance of the applet and displays it. When the applet is run standalone, the main method is invoked to create a frame (line 10) to hold the applet. The applet is created (line 13) and added to the frame (line 16). The frame is displayed in line 22. Note that you can add an applet to a container, but not a frame to a container. A frame is a top-level container that cannot be embedded in another container.<br />
<br />
✓<br />
<br />
18.6 How do you add components to a JApplet? What is the default layout manager of<br />
<br />
Check Point<br />
<br />
JApplet?<br />
<br />
18.7 Can you place a frame in an applet? 18.8 Can you place an applet in a frame? 18.9 What are the differences between applications and applets? How do you run an application, and how do you run an applet? Is the compilation process different for applications and applets?<br />
<br />
18.6 Applet Life-Cycle Methods The Web browser controls and executes applets using the applet life-cycle methods.<br />
<br />
Key Point<br />
<br />
Applets are actually run from the applet container, which is a plug-in of a Web browser. A plug-in is a software component that can be added into a larger software to provide additional functions. The Applet class contains the init(), start(), stop(), and destroy() methods, known as the life-cycle methods. These methods are called by the applet container to control the execution of an applet. They are implemented with an empty body in the Applet class, so they do nothing by default. You may override them in a subclass of Applet to perform desired operations. Figure 18.5 shows how the applet container calls these methods.<br />
<br />
Applet container creates the applet Loaded<br />
<br />
Applet container invokes init() Created<br />
<br />
Applet container invokes stop()<br />
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Applet container invokes start()<br />
<br />
Initialized<br />
<br />
applet container<br />
<br />
Started<br />
<br />
Stopped Applet container invokes start()<br />
<br />
Applet container loads the applet<br />
<br />
FIGURE 18.5<br />
<br />
Applet container invokes destroyed()<br />
<br />
Destroyed<br />
<br />
The applet container uses the init, start, stop, and destroy methods to control the applet.<br />
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678 Chapter 18<br />
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Applets and Multimedia<br />
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18.6.1 The init Method The init method is invoked after the applet is created. If a subclass of Applet has an initialization to perform, it should override this method. The functions usually implemented in this method include getting string parameter values from the <applet rel="nofollow"> tag in the HTML page.<br />
<br />
init()<br />
<br />
18.6.2<br />
<br />
The start Method<br />
<br />
The start method is invoked after the init method. It is also called when the user returns to the Web page containing the applet after surfing other pages. A subclass of Applet overrides this method if it has any operation that needs to be performed whenever the Web page containing the applet is visited. An applet with animation, for example, might start the timer to resume animation.<br />
<br />
start()<br />
<br />
18.6.3<br />
<br />
The stop Method<br />
<br />
The stop method is the opposite of the start method. The start method is called when the user moves back to the page that contains the applet. The stop method is invoked when the user leaves the page. A subclass of Applet overrides this method if it has any operation to be performed each time the Web page containing the applet is no longer visible. An applet with animation, for example, might stop the timer to pause animation.<br />
<br />
stop()<br />
<br />
18.6.4<br />
<br />
The destroy Method<br />
<br />
The destroy method is invoked when the browser exits normally to inform the applet that it is no longer needed and should release any resources it has allocated. The stop method is always called before the destroy method. A subclass of Applet overrides this method if it has any operation to be performed before it is destroyed. Usually, you won’t need to override this method unless you want to release specific resources that the applet created.<br />
<br />
destroy()<br />
<br />
✓<br />
<br />
Check Point<br />
<br />
18.10 Describe the init(), start(), stop(), and destroy() methods in the Applet 18.11<br />
<br />
class. Why does the applet in (a) below display nothing? Why does the applet in (b) have a runtime NullPointerException on the highlighted line?<br />
<br />
import javax.swing.*;<br />
<br />
import javax.swing.*;<br />
<br />
public class WelcomeApplet extends JApplet { public void WelcomeApplet() { JLabel jlblMessage = new JLabel("It is Java"); } }<br />
<br />
public class WelcomeApplet extends JApplet { private JLabel jlblMessage; public WelcomeApplet() { JLabel jlblMessage = new JLabel("It is Java"); } @Override public void init() {<br />
<br />
add(jlblMessage); } } (a)<br />
<br />
(b)<br />
<br />
18.7 Passing Strings to Applets 679<br />
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18.7 Passing Strings to Applets You can pass string parameters from an HTML file to an applet. In Section 9.7, Command-Line Arguments, you learned how to pass strings to Java applications from a command line. Strings are passed to the main method as an array of strings. When the application starts, the main method can use these strings. There is no main method in an applet, however, and applets are not run from the command line by the Java interpreter. How, then, can applets accept arguments? In this section, you will learn how to pass strings to Java applets. To be passed to an applet, a parameter must be defined in the HTML file and must be read by the applet when it is initialized. Parameters are defined using the <param> tag. The <param> tag must be embedded in the <applet rel="nofollow"> tag. Its syntax is: <param name = parametername value = stringvalue /><br />
<br />
The <param> tag defines a parameter and its corresponding string value.<br />
<br />
Note No comma separates the parameter name from the parameter value in the HTML code. The HTML parameter names are not case sensitive.<br />
<br />
Suppose you want to write an applet to display a message. The message is passed as a parameter. In addition, you want the message to be displayed at a specific location with xcoordinate and y-coordinate, which are passed as two parameters. The parameters and their values are listed in Table 18.1.<br />
<br />
TABLE 18.1 Parameter Names and Values for the DisplayMessage Applet Parameter Name<br />
<br />
Parameter Value<br />
<br />
MESSAGE<br />
<br />
"Welcome to Java"<br />
<br />
X<br />
<br />
20<br />
<br />
Y<br />
<br />
30<br />
<br />
The HTML source file is given in Listing 18.4.<br />
<br />
LISTING 18.4 DisplayMessage.html <html> <head> <title>Passing Strings to Java Applets This applet gets a message from the HTML page and displays it.
tag in an HTML file to tell the Web browser where to find the applet. The applet can accept string parameters from HTML using the tag, as shown below: { public int compareTo(T o) } represents a formal generic type, which can be replaced later with an actual concrete type. Replacing a generic type is called a generic instantiation. By convention, a single capital letter such as E or T is used to denote a formal generic type. To see the benefits of using generics, let us examine the code in Figure 21.2. The statement in Figure 21.2a declares that c is a reference variable whose type is Comparable and invokes the compareTo method to compare a Date object with a string. The code compiles fine, but it has a runtime error because a string cannot be compared with a date. c = new Date(); System.out.println(c.compareTo("red") ); and invokes the compareTo method to compare a Date object with a string. This code generates a compile error, because the argument passed to the compareTo method must be of the Date type. Since the errors can be detected at compile time rather than at runtime, the generic type makes the program more reliable. ArrayList was introduced in Section 11.11, The ArrayList Class. This class has been a generic class since JDK 1.5. Figure 21.3 shows the class diagram for ArrayList before and since JDK 1.5, respectively. list = new ArrayList(); intList = new ArrayList(); intList = new ArrayList(); list = new ArrayList(); list.add("Red"); list.add("White"); String s = list.get(0); // No casting is needed list = new ArrayList(); list.add(5.5); // 5.5 is automatically converted to new Double(5.5) list.add(3.0); // 3.0 is automatically converted to new Double(3.0) Double doubleObject = list.get(0); // No casting is needed double d = list.get(1); // Automatically converted to double dates = new ArrayList(); dates.add(new Date()); dates.add(new String()); dates = new ArrayList(); dates.add(new Date()); Date date = dates.get(0); -list: java.util.ArrayList { private java.util.ArrayList list = new java.util.ArrayList(); stack1 = new GenericStack(); stack1.push("London"); stack1.push("Paris"); stack1.push("Berlin"); stack2 = new GenericStack(); stack2.push(1); // autoboxing 1 to new Integer(1) stack2.push(2); stack2.push(3);, only strings can be added to the stack. It would be a compile error if you attempted to add an integer to stack1.(). This could mislead you into thinking that the constructor of GenericStack should be defined as public GenericStack().(), should the constructor in the ArrayList class be()print(integers); GenericMethodDemo.print(strings); } public static void print(E[] list) { for (int i = 0; i < list.length; i++) System.out.print(list[i] + " "); System.out.println(); } immediately after the keyword static in the method header. For example, void print(E[] list)print(integers); GenericMethodDemo.print(strings); (line 7) specifies that E is a generic subtype of GeometricObject. You must invoke equalArea by passing two instances of GeometricObject. boolean equalArea( E object1, E object2) { return object1.getArea() == object2.getArea(); } } is the same as .. To define a generic type for a method, place the generic type before the method return type, such as void max(E o1, E o2).> void sort(E[] list) { E currentMin; int currentMinIndex;> (line 36). This has two meanings. First, it specifies that E is a subtype of Comparable. Second, it specifies that the elements to be compared are of the E type as well. The sort method uses the compareTo method to determine the order of the objects in the array (line 46). Integer, Double, Character, and String implement Comparable, so the objects of these classes can be compared using the compareTo method. The program creates arrays of Integer objects, Double objects, Character objects, and String objects (lines 4–16) and invoke the sort method to sort these arrays (lines 19–22). stack = new GenericStack();> E max(E o1, E o2) { if (o1.compareTo(o2) > 0) return o1; else. As another example, in the following code you can declare a raw type stack in line 1, assign new GenericStack to it in line 2, and push a string and an integer object to the stack in lines 3 and 4. 1 2 3 4(); stack.push("Welcome to Java"); stack.push(new Integer(2)); intStack = new GenericStack(); intStack.push(1); // 1 is autoboxed into new Integer(1) intStack.push(2); intStack.push(-2); System.out.print("The max number is " + max(intStack)); } stack) { double max = stack.pop().doubleValue(); // Initialize max while (!stack.isEmpty()) { double value = stack.pop().doubleValue(); if (value > max) max = value; } return max; } }. Thus, you cannot invoke max(intStack). The fact is that Integer is a subtype of Number, but GenericStack is not a subtype of GenericStack. To circumvent this problem, use wildcard generic types. A wildcard generic type has three forms: ? and ? extends T, as well as ? super T, where T is a generic type. The first form, ?, called an unbounded wildcard, is the same as ? extends Object. The second form, ? extends T, called a bounded wildcard, represents T or an unknown subtype of T. The third form, ? super T, called a lower-bound wildcard, denotes T or an unknown supertype of T. You can fix the error by replacing line 12 in Listing 21.7 as follows: public static double max(GenericStack stack) {()) or max(new GenericStack()). Listing 21.8 shows an example of using the ? wildcard in the print method that prints objects in a stack and empties the stack. is a wildcard that represents any object type. It is equivalent to . What happens if you replace GenericStack with GenericStack? It would be wrong to invoke print(intStack), because intStack is not an instance of GenericStack. Please note that GenericStack is not a subtype of GenericStack, even though Integer is a subtype of Object. intStack = new GenericStack(); intStack.push(1); // 1 is autoboxed into new Integer(1) intStack.push(2); intStack.push(-2); print(intStack); } /** Prints objects and empties the stack */ public static void print(GenericStack stack) { while (!stack.isEmpty()) { System.out.print(stack.pop() + " "); } } }, a compile error will occur on add(stack1, stack2) in line 8, because stack1’s type is GenericStack and stack2’s type is GenericStack. represents type T or a supertype of T. Object is a supertype of String. stack1 = new GenericStack(); GenericStack stack2 = new GenericStack(); stack2.push("Java"); stack2.push(2); stack1.push("Sun"); add(stack1, stack2); AnyWildCardDemo.print(stack2); } void add(GenericStack stack1, GenericStack stack2) { while (!stack1.isEmpty()) stack2.push(stack1.pop()); } void add(GenericStack stack1, GenericStack stack2)? 21.15 What are an unbounded wildcard, a bounded wildcard, and a lower-bound wildcard? 21.16 What happens if lines 12–13 in Listing 21.9 are changed to public static void add(GenericStack stack1, GenericStack stack2) void add(GenericStack stack1, GenericStack stack2) list = new ArrayList (); list.add("Oklahoma"); String state = list.get(0); void print(E [] list) { for (int i = 0; i < list.length; i++) System.out.print(list[i] + " "); System.out.println(); } boolean equalArea( E object1, E object2) { return object1.getArea() == object2.getArea(); } (a) list1 = new ArrayList(); ArrayList list2 = new ArrayList(); and ArrayList are two types at compile time, only one ArrayList class is loaded into the JVM at runtime. list1 and list2 are both instances of ArrayList, so the following statements display true: System.out.println(list1 instanceof ArrayList); System.out.println(list2 instanceof ArrayList); is wrong. Since ArrayList is not stored as a separate class in the JVM, using it at runtime makes no sense. Because generic types are erased at runtime, there are certain restrictions on how generic types can be used. Here are some of the restrictions: Restriction 1: Cannot Use new E() You cannot create an instance using a generic type parameter. For example, the following statement is wrong: E object = new E();[] list = new ArrayList[10];[] list = (ArrayList[])new ArrayList[10]; { public static void m(E o1) { // Illegal } public static E o1; // Illegal static { E o2; // Illegal } } extends Exception { } as follows: try { ... } catch (MyException ex) { ... } and ArrayList, does the JVM 21.20 21.21 21.22 in line 1 specifies that the generic type is a subtype of Number. Three abstract methods—add, multiply, and zero—are defined in lines 3, 6, and 9. These methods are abstract because we cannot implement them without knowing the exact type of the elements. The addMaxtrix (lines 12–30) and multiplyMatrix (lines 33–57) methods implement the methods for adding and multiplying two matrices. All these methods must be nonstatic, because they use generic type E for the class. The printResult method (lines 60–84) is static because it is not tied to specific instances. The matrix element type is a generic subtype of Number. This enables you to use an object of any subclass of Number as long as you can implement the abstract add, multiply, and zero methods in subclasses. The addMatrix and multiplyMatrix methods (lines 12–57) are concrete methods. They are ready to use as long as the add, multiply, and zero methods are implemented in the subclasses. The addMatrix and multiplyMatrix methods check the bounds of the matrices before performing operations. If the two matrices have incompatible bounds, the program throws an exception (lines 16, 36). { /** Abstract method for adding two elements of the matrices */ protected abstract E add(E o1, E o2); in line 1. After the generic instantiation, the add method in GenericMatrix is now Integer add(Integer o1, Integer o2). The add, multiply, and zero methods are implemented for Integer objects. These methods are still protected, because they are invoked only by the addMatrix and multiplyMatrix methods. Listing { @Override /** Add two integers */ protected Integer add(Integer o1, Integer o2) { return o1 + o2; } @Override /** Multiply two integers */ protected Integer multiply(Integer o1, Integer o2) { return o1 * o2; } @Override /** Specify zero for an integer */ protected Integer zero() { return 0; } in line 1. After the generic instantiation, the add method in GenericMatrix is now Rational add(Rational r1, Rational r2). The add, multiply, and zero methods are implemented for Rational objects. These methods are still protected, because they are invoked only by the addMatrix and multiplyMatrix methods. { @Override /** Add two rational numbers */ protected Rational add(Rational r1, Rational r2) { return r1.add(r2); } @Override /** Multiply two rational numbers */ protected Rational multiply(Rational r1, Rational r2) { return r1.multiply(r2); } @Override /** Specify zero for a Rational number */ protected Rational zero() { return new Rational(0, 1); } } ArrayList removeDuplicates(ArrayList list)> void insertionSort(E[] list)> E max(E[] list)> E max(E[][] list)> int binarySearch(E[] list, E key) void shuffle(ArrayList list)> void sort(ArrayList list)> E max(ArrayList list) +add(o: E): boolean +addAll(c: Collection): boolean +clear(): void +contains(o: Object): boolean +containsAll(c: Collection): boolean +equals(o: Object): boolean +hashCode(): int +isEmpty(): boolean +remove(o: Object): boolean +removeAll(c: Collection): boolean +retainAll(c: Collection): boolean +size(): int +toArray(): Object[] +hasNext(): boolean +next(): E +remove(): void collection1 = new ArrayList(); collection1.add("New York"); collection1.add("Atlanta"); collection1.add("Dallas"); collection1.add("Madison"); collection2 = new ArrayList(); collection2.add("Seattle"); collection2.add("Portland"); collection2.add("Los Angeles"); collection2.add("Atlanta"); System.out.println("\nA list of cities in collection2:"); System.out.println(collection2); ArrayList c1 = (ArrayList)(collection1.clone() ); c1.addAll(collection2); System.out.println("\nCities in collection1 or collection2: "); System.out.println(c1); c1 = (ArrayList)(collection1.clone()); c1.retainAll(collection2); System.out.print("\nCities in collection1 and collection2: "); System.out.println(c1); c1 = (ArrayList)(collection1.clone()); c1.removeAll(collection2); System.out.print("\nCities in collection1, but not in 2: "); System.out.println(c1); } } collection = new ArrayList(); collection.add("New York"); collection.add("Atlanta"); collection.add("Dallas"); collection.add("Madison"); Iterator iterator = collection.iterator(); while (iterator.hasNext()) { System.out.print(iterator.next() .toUpperCase() + " "); } System.out.println(); } } +add(index: int, element: Object): boolean +remove(index: int): E +add(o: E): void +hasPrevious(): boolean +nextIndex(): int +previous(): E +previousIndex(): int +set(o: E): void +ArrayList() +ArrayList(c: Collection) +ArrayList(initialCapacity: int) +trimToSize(): void +LinkedList() +LinkedList(c: Collection) +addFirst(o: E): void +addLast(o: E): void +getFirst(): E +getLast(): E +removeFirst(): E +removeLast(): E arrayList = new ArrayList(); arrayList.add(1); // 1 is autoboxed to new Integer(1) arrayList.add(2); arrayList.add(3); arrayList.add(1); arrayList.add(4); arrayList.add(0, 10); arrayList.add(3, 30); System.out.println("A list of integers in the array list:"); System.out.println(arrayList); LinkedList linkedList = new LinkedList(arrayList); linkedList.add(1, "red"); linkedList.removeLast(); linkedList.addFirst("green"); System.out.println("Display the linked list forward:"); ListIterator listIterator = linkedList.listIterator(); while (listIterator.hasNext()) { System.out.print(listIterator.next() + " "); } System.out.println(); System.out.println("Display the linked list backward:"); listIterator = linkedList.listIterator(linkedList.size()); while (listIterator.hasPrevious()) { System.out.print(listIterator.previous() + " "); } } } list1 = Arrays.asList("red", "green", "blue"); List list2 = Arrays.asList(10, 20, 30, 40, 50); interface. The Comparator interface has two methods, compare and equals. ■ public int compare(T element1, T element2) , java.io.Serializable { public int compare(GeometricObject o1, GeometricObject o2) { double area1 = o1.getArea(); double area2 = o2.getArea(); if (area1 < area2) return -1; else if (area1 == area2) return 0; else return 1; } }. Line 5 overrides the compare method to compare two geometric objects. The class also implements Serializable. It is generally a good idea for comparators to implement Serializable, as they may be used as ordering methods in serializable data structures. In order for the data structure to serialize successfully, the comparator (if provided) must implement Serializable. Listing 22.5 gives a method that returns a larger object between two geometric objects. The objects are compared using the GeometricObjectComparator. c ) { if (c.compare(g1, g2) > 0) return g1; else return g2; } list = Arrays.asList("red", "green", "blue"); Collections.sort(list); System.out.println(list); list = Arrays.asList("yellow", "red", "green", "blue"); Collections.sort(list, Collections.reverseOrder() ); System.out.println(list); list1 = Arrays.asList(2, 4, 7, 10, 11, 45, 50, 59, 60, 66); System.out.println("(1) Index: " + Collections.binarySearch(list1, 7)); System.out.println("(2) Index: " + Collections.binarySearch(list1, 9)); List 