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A Comprehensive Introduction
to Object-Oriented Programming
with JavaTM
C.Thomas Wu
Naval Postgraduate School
wu23399_fm.qxd 1/10/07 11:53 Page i

A COMPREHENSIVE INTRODUCTION TO OBJECT-ORIENTED PROGRAMMING WITH JAVA
Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas,
New York, NY 10020. Copyright © 2008 by The McGraw-Hill Companies, Inc. All rights reserved. No part of this
publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system,
without the prior written consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any network
or other electronic storage or transmission, or broadcast for distance learning.
Some ancillaries, including electronic and print components, may not be available to customers outside
the United States.
This book is printed on acid-free paper.
1 2 3 4 5 6 7 8 9 0 DOC/DOC 0 9 8 7
ISBN 978–0–07–352339–2
MHID 0–07–352339–9
Publisher: Alan R. Apt
Executive Marketing Manager: Michael Weitz
Senior Project Manager: Sheila M. Frank
Lead Production Supervisor: Sandy Ludovissy
Associate Media Producer: Christina Nelson
Designer: Rick D. Noel
Cover Designer: Elise Lansdon
(USE) Cover Image: breaking wave on foaming ocean surface, ®Ron Dahlquist/Getty Images
Compositor: ICC Macmillan Inc.
Typeface: 10.5/12 Times Roman
Printer: R. R. Donnelley Crawfordsville, IN
Library of Congress Cataloging-in-Publication Data
Wu, C. Thomas.
A comprehensive introduction to object-oriented programming with Java / C. Thomas
Wu. – 1st ed.
p. cm.
ISBN 978–0–07–352339–2 — ISBN 0–07–352339–9
1. Object-oriented programming (Computer science) 2. Java (Computer program
language) I. Title.
QA76.64.W77 2008
005.117–dc22
2006048064
www.mhhe.com
wu23399_fm.qxd 1/10/07 11:53 Page ii

To my family
wu23399_fm.qxd 1/10/07 11:53 Page iii

wu23399_fm.qxd 1/10/07 11:53 Page iv

v
Preface xiii
Key Differences from the Standard Edition xiii
Book Organization xiv
Hallmark Features of the Text xviii
0 Introduction to Computers and
Programming Languages 1
0.1 A History of Computers 2
0.2 Computer Architecture 4
0.3 Programming Languages 11
0.4 Java 12
1 Introduction to Object-Oriented Programming and
Software Development 15
1.1 Classes and Objects 16
1.2 Messages and Methods 18
1.3 Class and Instance Data Values 20
1.4 Inheritance 23
1.5 Software Engineering and Software
Life Cycle 24
C o n t e n t s
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2 Getting Started with Java 29
2.1 The First Java Program 30
2.2 Program Components 39
2.3 Edit-Compile-Run Cycle 49
2.4 Sample Java Standard Classes 52
2.5 Sample Development 67
3 Numerical Data 81
3.1 Variables 82
3.2 Arithmetic Expressions 90
3.3 Constants 95
3.4 Displaying Numerical Values 97
3.5 Getting Numerical Input 103
3.6 The Math Class 109
3.7 Random Number Generation 113
3.8 The GregorianCalendar Class 115
3.10 Numerical Representation (Optional) 131
4 Defining Your Own Classes—Part 1 145
4.1 First Example:Defining and Using a Class 146
4.2 Second Example:Defining and Using Multiple Classes 156
4.3 Matching Arguments and Parameters 160
4.4 Passing Objects to a Method 162
4.5 Constructors 167
4.6 Information Hiding and Visibility Modifiers 172
4.7 Class Constants 175
4.8 Local Variables 183
4.9 Calling Methods of the Same Class 185
4.10 Changing Any Class to a Main Class 189
vi Contents
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Contents vii
5 Selection Statements 213
5.1 The if Statement 214
5.2 Nested if Statements 225
5.3 Boolean Expressions and Variables 231
5.4 Comparing Objects 239
5.5 The switch Statement 244
5.6 Drawing Graphics 248
5.7 Enumerated Constants 258
6 Repetition Statements 295
6.1 The while Statement 296
6.2 Pitfalls in Writing Repetition Statements 305
6.3 The do–while Statement 311
6.4 Loop-and-a-Half Repetition Control 315
6.5 The for Statement 319
6.6 Nested for Statements 324
6.7 Formatting Output 326
6.8 Loan Tables 331
6.9 Estimating the Execution Time 334
6.10 Recursive Methods (Optional) 338
7 Defining Your Own Classes—Part 2 365
7.1 Returning an Object from a Method 366
7.2 The Reserved Word this 370
7.3 Overloaded Methods and Constructors 378
7.4 Class Variables and Methods 383
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viii Contents
7.5 Call-by-Value Parameter Passing 387
7.6 Organizing Classes into a Package 394
7.7 Using Javadoc Comments for Class Documentation 395
7.8 The Complete Fraction Class 400
8 Exceptions and Assertions 437
8.1 Catching Exceptions 438
8.2 Throwing Exceptions and Multiple catch Blocks 445
8.3 Propagating Exceptions 450
8.4 Types of Exceptions 458
8.5 Programmer-Defined Exceptions 461
8.6 Assertions 463
9 Characters and Strings 487
9.1 Characters 488
9.2 Strings 491
9.3 Pattern Matching and Regular Expression 502
9.4 The Pattern and Matcher Classes 509
9.5 Comparing Strings 513
9.6 StringBuffer and StringBuilder 515
10 Arrays and Collections 543
10.1 Array Basics 544
10.2 Arrays of Objects 555
10.3 The For-Each Loop 565
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Contents ix
10.4 Passing Arrays to Methods 569
10.5 Two-Dimensional Arrays 576
10.6 Lists and Maps 583
11 Sorting and Searching 619
11.1 Searching 620
11.2 Sorting 624
11.3 Heapsort 632
12 File Input and Output 669
12.1 File and JFileChooser Objects 670
12.2 Low-Level File I/O 679
12.3 High-Level File I/O 684
12.4 Object I/O 693
13 Inheritance and Polymorphism 713
13.1 A Simple Example 714
13.2 Defining Classes with Inheritance 717
13.3 Using Classes Effectively with Polymorphism 721
13.4 Inheritance and Member Accessibility 724
13.5 Inheritance and Constructors 729
13.6 Abstract Superclasses and Abstract Methods 733
13.7 Inheritance versus Interface 738
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x Contents
14 GUI and Event-Driven Programming 765
14.1 Simple GUI I/O with JOptionPane 768
14.2 Customizing Frame Windows 771
14.3 GUI Programming Basics 777
14.4 Text-Related GUI Components 787
14.5 Layout Managers 798
14.6 Effective Use of Nested Panels 808
14.7 Other GUI Components 817
14.8 Menus 835
14.9 Handling Mouse Events 839
15 Recursive Algorithms 859
15.1 Basic Elements of Recursion 860
15.2 Directory Listing 861
15.3 Anagram 863
15.4 Towers of Hanoi 866
15.5 Quicksort 868
15.6 When Not to Use Recursion 873
16 Memory Allocation Schemes and
Linked Data Structures 879
16.1 Contiguous Memory Allocation Scheme 881
16.2 Noncontiguous Memory Allocation Scheme 886
16.3 Manipulating Linked Lists 890
16.4 Linked Lists of Objects 903
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Contents xi
17 Generics and Type Safety 945
17.1 Generic Classes 946
17.2 Generics and Collections 961
17.3 Generics,Inheritance,and Java Interface 969
17.4 Additional Topics and Pitfalls 974
18 List ADT 981
18.1 The List ADT 982
18.2 The List Interface 988
18.3 The Array Implementation of the List ADT 992
18.4 The Linked-List Implementation
of the List ADT 1001
18.5 The Linked Implementation
with the Head Node 1018
18.6 The Iterator Design Pattern 1022
19 Stack ADT 1035
19.1 The Stack ADT 1036
19.2 The Stack Interface 1040
19.3 The Array Implementation 1042
19.4 The Linked-List Implementation 1047
19.5 Implementation Using NPSList 1052
19.6 Sample Applications:Matching HTML Tags 1053
19.7 Sample Applications:Solving
a Maze with Backtracking 1060
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xii Contents
20 Queue ADT 1069
20.1 The Queue ADT 1070
20.2 The Queue Interface 1073
20.3 The Array Implementation 1075
20.4 The Linked-List Implementation 1082
20.5 Implementation Using NPSList 1088
20.6 Priority Queue 1089
Appendix A 1099
Appendix B 1107
Appendix C 1133
Appendix D 1155
Index 1163
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xiii
P r e f a c e
This book is an in-depth introduction to object-oriented programming using
the Java programming language. In addition to covering traditional topics for a CS1
course, some of the more advanced topics such as recursion and linked lists are in-
cluded to provide a comprehensive coverage of beginning to intermediate-level ma-
terials. There are more materials in the book than what are normally covered in a
typical CS1 course. An instructor may want to teach some of the chapters on data
structures in an advanced CS1 course. Topics covered in Chapters 16 to 20 are also
suitable for use in a CS2 course.
Key Differences from the Standard Edition
This comprehensive edition is based on An Introduction to Object-Oriented Pro-
gramming with Java, Fourth Edition. The key differences between this comprehen-
sive version and the fourth edition standard version are as follows:
1. Data Structures Chapters. Chapter 16 covers topics on managing linked
nodes. Using this as the foundation, Chapters 18 through 20 present three ab-
stract data types (ADTs) List, Stack, and Queue, respectively. For all three
ADTs, both array-based and linked-list implementations are shown, and their
relative advantages and disadvantages are discussed.
2. More Discussion on Java 5.0 Features. Many of the new Java 5.0 features
are explained and used in the sample programs. They include the enumerator
type, the for-each loop construct, auto boxing and unboxing, and the generics.
One complete chapter (Chapter 17) is dedicated to the generics.
3. Exclusive Use of Console Input and Output. All the GUI related topics,
including the JOptionPane class, are moved to Chapter 14. Sample programs
before Chapter 14 use the standard console input (Scanner) and output
(System.out). Those who want to use JOptionPane for simple input and output
can do so easily by covering Section 14.1 before Chapter 3.
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xiv Preface
Book Organization
There are 21 chapters in this book, numbered from 0 to 20. The first 11 chapters
cover the core topics that provide the fundamentals of programming. Chapters 11 to
15 cover intermediate-level topics such as sorting, searching, recursion, inheritance,
polymorphism, and file I/O. And Chapters 16 to 20 cover topics related to data
structures. There are more than enough topics for one semester. After the first
11 chapters (Ch 0 to Ch 10), instructors can mix and match materials from Chapters 11
to 20 to suit their needs. We first show the dependency relationships among the
chapters and then provide a brief summary of each chapter.
Chapter Dependency
For the most part, chapters should be read in sequence, but some variations are
possible, especially with the optional chapters. Here’s a simplified dependency
graph:
0
1
2
3
4
5
6
7
8 9 10
15
14*
13
12
11
18
19 20
17
16
*Note: Some examples use arrays,
but the use of arrays is not an
integral part of the examples.
These examples can be modified
to those that do not use arrays.
Many topics from the early part
of the chapter can be introduced
as early as after Chapter 2.
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Preface xv
Brief Chapter Summary
Here is a short description of each chapter:
• Chapter 0 is an optional chapter. We provide background information on
computers and programming languages. This chapter can be skipped or as-
signed as an outside reading if you wish to start with object-oriented pro-
gramming concepts.
• Chapter 1 provides a conceptual foundation of object-oriented programming.
We describe the key components of object-oriented programming and illus-
trate each concept with a diagrammatic notation using UML.
• Chapter 2 covers the basics of Java programming and the process of editing,
compiling, and running a program. From the first sample program presented in
this chapter, we emphasize object-orientation. We will introduce the standard
classes String, Date, and SimpleDateFormat so we can reinforce the notion of
object declaration, creation, and usage. Moreover, by using these standard
classes, students can immediately start writing practical programs.We describe
and illustrate console input with System.in and the new Scanner class and output
with System.out.
• Chapter 3 introduces variables, constants, and expressions for manipulating
numerical data. We explain the standard Math class from java.lang and
introduce more standard classes (GregorianCalendar and DecimalFormat) to
continually reinforce the notion of object-orientation. We describe additional
methods of the Scanner class to input numerical values. Random number
generation is introduced in this chapter. The optional section explains how the
numerical values are represented in memory space.
• Chapter 4 teaches the basics of creating programmer-defined classes. We
keep the chapter accessible by introducting only the fundamentals with illus-
trative examples. The key topics covered in this chapter are constructors, vis-
ibility modifiers (public and private), local variables, and passing data to
methods. We provide easy-to-grasp illustrations that capture the essence of
the topics so the students will have a clear understanding of them.
• Chapter 5 explains the selection statements if and switch. We cover boolean
expressions and nested-if statements. We explain how objects are compared
by using equivalence (==) and equality (the equals and compareTo methods).
We use the String and the programmer-defined Fraction classes to make the
distinction between the equivalence and equality clear. Drawing 2-D graphics
is introduced, and a screensaver sample development program is developed.
We describe the new Java 5.0 feature called enumerated type in this chapter.
• Chapter 6 explains the repetition statements while, do–while, and for. Pitfalls
in writing repetition statements are explained. One of the pitfalls to avoid is
the use of float or double for the data type of a counter variable. We illustrate
this pitfall by showing a code that will result in infinite loop. Finding the great-
est common divisor of two integers is used as an example of a nontrivial loop
statement. We show the difference between the straightforward (brute-force)
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xvi Preface
and the clever (Euclid’s) solutions. We introduce the Formatter class (new to
Java 5.0) and show how the output can be aligned nicely. The optional last sec-
tion of the chapter introduces recursion as another technique for repetition.
The recursive version of a method that finds the greatest common divisor of
two integers is given.
• Chapter 7 is the second part of creating programmer-defined classes. We
introduce new topics related to the creation of programmer-defined classes
and also repeat some of the topics covered in Chapter 4 in more depth. The
key topics covered in this chapter are method overloading, the reserved
word this, class methods and variables, returning an object from a method,
and pass-by-value parameter passing. As in Chapter 4, we provide many
lucid illustrations to make these topics accessible to beginners. We use the
Fraction class to illustrate many of these topics, such as the use of this and
class methods. The complete definition of the Fraction class is presented in
this chapter.
• Chapter 8 teaches exception handling and assertions. The focus of this chap-
ter is the construction of reliable programs. We provide a detailed coverage of
exception handling in this chapter. We introduce an assertion and show how it
can be used to improve the reliability of finished products by catching logical
errors early in the development.
• Chapter 9 covers nonnumerical data types: characters and strings. Both the
String and StringBuffer classes are explained in the chapter. Another string
class named StringBuilder (new to Java 5.) is briefly explained in this chapter.
An important application of string processing is pattern matching. We describe
pattern matching and regular expression in this chapter. We introduce the
Pattern and Matcher classes and show how they are used in pattern matching.
• Chapter 10 teaches arrays. We cover arrays of primitive data types and of ob-
jects. An array is a reference data type in Java, and we show how arrays are
passed to methods. We describe how to process two-dimensional arrays and
explain that a two-dimensional array is really an array of arrays in Java. Lists
and maps are introduced as a more general and flexible way to maintain a col-
lection of data. The use of ArrayList and HashMap classes from the java.util
package is shown in the sample programs. Also, we show how the WordList
helper class used in Chapter 9 sample development program is implemented
with another map class called TreeMap.
• Chapter 11 presents searching and sorting algorithms. Both N2
and Nlog2N
sorting algorithms are covered. The mathematical analysis of searching and
sorting algorithms can be omitted depending on the students’ background.
• Chapter 12 explains the file I/O. Standard classes such as File and JFile-
Chooser are explained. We cover all types of file I/O, from a low-level byte
I/O to a high-level object I/O. We show how the file I/O techniques are used
to implement the helper classes—Dorm and FileManager—in Chapter 8 and 9
sample development programs. The use of the Scanner class for inputting data
from a textfile is also illustrated in this chapter.
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Preface xvii
• Chapter 13 discusses inheritance and polymorphism and how to use them ef-
fectively in program design. The effect of inheritance for member accessibil-
ity and constructors is explained. We also explain the purpose of abstract
classes and abstract methods.
• Chapter 14 covers GUI and event-driven programming. Only the Swing-
based GUI components are covered in this chapter. We show how to use the
JOptionPane class for a very simple GUI-based input and output. GUI com-
ponents introduced in this chapter include JButton, JLabel, ImageIcon,
JTextField, JTextArea, and menu-related classes. We describe the effective use
of nested panels and layout managers. Handling of mouse events is described
and illustrated in the sample programs. Those who do not teach GUI can skip
this chapter altogether. Those who teach GUI can introduce the beginning part
of the chapter as early as after Chapter 2.
• Chapter 15 covers recursion. Because we want to show the examples where
the use of recursion really shines, we did not include any recursive algorithm
(other than those used for explanation purposes) that really should be written
nonrecursively.
• Chapter 16 covers contiguous and noncontiguous memory allocation schemes
and introduces the concept of linked lists. Ample examples are provided to
illustrate the manipulation of linked lists of primitive data types and linked
lists of objects. This chapter lays the necessary foundation for the students to
learn different techniques for implementing the abstract data types covered in
Chapters 18 through 20.
• Chapter 17 covers new Java 5.0 generics in detail. The chapter describes how
generic classes are defined and how the type safety is supported by generics.
A concrete example of using generics is shown by defining a simple linked list
with generic nodes.
• Chapter 18 introduces the concept of abstract data types (ADT) and covers
the List ADT. Key features of the List ADT are explained and two implemen-
tations using an array and a linked list are shown. The iterator pattern to tra-
verse the elements in the List ADT is introduced.
• Chapter 19 covers the Stack ADT. Key features of the Stack ADT are ex-
plained and two implementations using an array and a linked list are shown.
Sample applications that use stacks are described.
• Chapter 20 covers the Queue ADT. Key features of the Stack ADT are ex-
plained and two implementations using an array and a linked list are shown.
A special type of queue called a priority queue is also intoduced in this
chapter.
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xviii Preface
Development Exercises
give students an opportunity
to practice incremental
development.
Hallmark Features of the Text
Problem Solving
Printing the Initials
Now that we have acquired a basic understanding of Java application programs, let’s
write a new application.We will go through the design,coding,and testing phases of the
software life cycle to illustrate the development process. Since the program we develop
here is very simple,we can write it without really going through the phases.However,it is
extremely important for you to get into a habit of developing a program by following the
software life cycle stages. Small programs can be developed in a haphazard manner, but
not large programs.We will teach you the development process with small programs first,
so you will be ready to use it to create large programs later.
We will develop this program by using an incremental development technique,
which will develop the program in small incremental steps. We start out with a bare-
bones program and gradually build up the program by adding more and more code to
it. At each incremental step, we design, code, and test the program before moving on
to the next step. This methodical development of a program allows us to focus our at-
tention on a single task at each step, and this reduces the chance of introducing errors
into the program.
Problem Statement
We start our development with a problem statement. The problem statement for our
sample programs will be short,ranging from a sentence to a paragraph,but the problem
statement for complex and advanced applications may contain many pages. Here’s the
problem statement for this sample development exercise:
Write an application that asks for the user’s first, middle, and last names and
replies with the user’s initials.
Overall Plan
Our first task is to map out the overall plan for development.We will identify classes nec-
essary for the program and the steps we will follow to implement the program.We begin
with the outline of program logic.For a simple program such as this one,it is kind of obvi-
ous; but to practice the incremental development, let’s put down the outline of program
flow explicitly.We can express the program flow as having three tasks:
1. Get the user’s first,middle,and last names.
2. Extract the initials to formulate the monogram.
3. Output the monogram.
Having identified the three major tasks of the program, we will now identify the
classes we can use to implement the three tasks. First, we need an object to handle the
input. At this point, we have learned about only the Scanner class, so we will use it
here. Second, we need an object to display the result. Again, we will use System.out, as
it is the only one we know at this point for displaying a string value. For the string
Sample Development
2.5 Sample Development
program
tasks
Sample Development Programs
Most chapters include a sample
development section that describes the
process of incremental development.
Development Exercises
For the following exercises, use the incremental development methodology to
implement the program. For each exercise, identify the program tasks, create a
design document with class descriptions, and draw the program diagram. Map
out the development steps at the start. Present any design alternatives and
justify your selection. Be sure to perform adequate testing at the end of each
development step.
8. In the sample development, we developed the user module of the keyless
entry system. For this exercise, implement the administrative module that
allows the system administrator to add and delete Resident objects and
modify information on existing Resident objects. The module will also allow
the user to open a list from a file and save the list to a file. Is it proper to
implement the administrative module by using one class? Wouldn’t it be a
better design if we used multiple classes with each class doing a single,
well-defined task?
9. Write an application that maintains the membership lists of five social clubs
in a dormitory. The five social clubs are the Computer Science Club, Biology
Club, Billiard Club, No Sleep Club, and Wine Tasting Club. Use the Dorm
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Preface xix
Object-Oriented Approach
We take the object-first approach to teaching object-oriented programming with emphasis
on proper object-oriented design.The concept of objects is clearly illustrated from the very
first sample program.
/*
Chapter 2 Sample Program: Displaying a Window
File: Ch2Sample1.java
*/
import javax.swing.*;
class Ch2Sample1 {
public static void main(String[] args) {
JFrame myWindow;
myWindow = new JFrame();
myWindow.setSize(300, 200);
myWindow.setTitle(My First Java Program);
myWindow.setVisible(true);
}
}
Dorm
Door
Resident
User module
Dorm Resident
A helper class
provided to us
A class we
implement
One or more classes
we implement
Administrative
module
Figure 8.8 Program diagrams for the user and administrative modules.Notice the same Dorm and
Resident classes are used in both programs.User and administrative modules will include one or more
classes (at least one is programmer-defined).
Good practices on object-
oriented design are
discussed throughout
the book and illustrated
through numerous
sample programs.
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xx Preface
Illustrative Diagrams
Illustrative diagrams are used to explain all key concepts of programming such as the
difference between object declaration and creation,the distinction between the primitive
data type and the reference data type,the call-by-value parameter passing,inheritance,and
many others.
Numerical Data Object
number1 = 237;
number2 = number1;
int number1, number2;
alan = new Professor();
turing = alan;
Professor alan, turing;
number2
number1
turing
alan
number2
number1
turing
alan
number1 = 237;
number2 = number1; turing = alan;
:Professor
:Professor
number2
number1
turing
alan
number1 = 237;
number2 = number1; turing = alan;
237
237
237
Figure 3.3 An effect of assigning the content of one variable to another.
Figure 18.2 Sample version 2 add operations on myList.
Before
After
Before
After
“cat” “gnu” “ape” “dog” “bee”
0 1 2 3 4
“cat”
0
“ape”
1
“dog”
2
“bee”
3
add(1, “gnu”)
throws
index-out-of-bounds-exception
add(5, “gnu”)
myList
“cat”
0
“ape”
1
“dog”
2
“bee”
3
myList
myList
myList
“cat”
0
“ape”
1
“dog”
2
“bee”
3
No structural
change to the list
Lucid diagrams are used effectively to explain
data structures and abstract data types.
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Preface xxi
Student Pedagogy
Always define a constructor and initialize data members fully in the
constructor so an object will be created in a valid state.
It is not necessary to create an object for every variable we use. Many novice pro-
grammers often make this mistake.For example,we write
Fraction f1, f2;
f1 = new Fraction(24, 36);
f2 = f1.simplify( );
We didn’t write
Fraction f1, f2;
f1 = new Fraction(24, 36);
f2 = new Fraction(1, 1); //not necessary
f2 = f1.simplify( );
because it is not necessary.The simplify method returns a Fraction object, and in
the calling program, all we need is a name we can use to refer to this returned
Fraction object.Don’t forget that the object name (variable) and the actual object
instance are two separate things.
We can turn our simulation program into a real one by replacing the Door
class with a class that actually controls the door. Java provides a mechanism
called Java Native Interface (JNI) which can be used to embed a link to a low-
level device driver code, so calling the open method actually unlocks the
door.
1. What will be displayed on the console window when the following code is
executed and the user enters abc123 and 14?
Scanner scanner = new Scanner(System.in);
try {
int num1 = scanner.nextInt();
System.out.println(Input 1 accepted);
int num2 = scanner.nextInt();
System.out.println(Input 2 accepted);
} catch (InputMismatchException e) {
System.out.println(Invalid Entry);
}
List the catch blocks in the order of specialized to more general exception classes.
At most one catch block is executed,and all other catch blocks are ignored.
Design Guidelines
provide tips on good
program design.
Things to Remember
boxes provide tips for
students to remember key
concepts.
Tips,Hints,and Pitfalls
provide important points
for which to watch out.
You Might Want to Know
boxes give students
interesting bits of
information.
Quick Check
exercises at the end of
the sections allow
students to test their
comprehension of
topics.
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xxii Preface
Supplements for Instructors and Students
On-Line Learning Center is located at www.mhhe.com/wu
For Instructors
• Complete set of PowerPoints, including lecture notes and figures.
• Complete solutions for the exercises
• Example Bank—Additional examples, which are searchable by topic, are
provided online in a “bank” for instructors.
• Homework Manager/Test Bank—Conceptual review questions are stored in
this electronic question bank and can be assigned as exam questions or home-
work.
• Online labs which accompany this text, can be used in a closed lab, open lab,
or for assigned programming projects.
wu23399_fm.qxd 1/10/07 11:55 Page xxii

Preface xxiii
For Students
• Compiler How Tos provide tutorials on how to get up and running on the
most popular compilers to aid students in using IDEs.
• Interactive Quizzes allow students to test what they learn and get immediate
feedback.
• Source code for all example programs in the book.
• Answers to quick check exercises.
• Glossary of key terms.
• Recent News links relevant to computer science.
• AdditionalTopics such as more on swing and an introduction to data structures.
Acknowledgments
First, I would like to thank the following reviewers for their comments, suggestions,
and encouragement.
Wu Focus Group—Jackson Hole, WY
Elizabeth Adams, James Madison University
GianMario Besana, Depaul University
Michael Buckley, State University of New York, Buffalo
James Cross, Auburn University
Priscilla Dodds, Georgia Perimeter College
Christopher Eliot, University of Massachusetts-Amherst
Joanne Houlahan, John Hopkins University
Len Myers, California Polytechnic State University, San Luis Obispo
Hal Perkins, University of Washington
William Shea, Kansas State University
Marge Skubic, University of Missouri, Columbia
Bill Sverdlik, Eastern Michigan University
Suzanne Westbrook, University of Arizona
wu23399_fm.qxd 1/10/07 11:55 Page xxiii

xxiv Preface
Reviewers
Ajith, Abraham, Oklahoma State University
Elizabeth Adams, James Madison University
David L. Atkins, University of Oregon
GianMario Besana, DePaul University
Robert P. Burton, Brigham Young University
Michael Buckley, State University of New York, Buffalo
Rama Chakrapani, Tennessee Technological University
Teresa Cole, Boise State University
James Cross, Auburn University
Priscilla Dodds, Georgia Perimeter College
Kossi Delali Edoh, Montclair State University
Christopher Eliot, University of Massachusetts-Amherst
Michael Floeser, Rochester Institute of Technology
Joanne Houlahan, John Hopkins University
Michael N. Huhns, University of South Carolina
Eliot Jacobson, University of California, Santa Barbara
Martin Kendall, Montgomery Community College
Mike Litman, Western Illinois University
Len Myers, California Polytechnic State University, San Luis Obispo
Jun Ni, University of Iowa
Robert Noonan, College of William and Mary
Jason S. O’Neal, Mississippi College
Hal Perkins, University of Washington
Gerald Ross, Lane Community College
William Shea, Kansas State University
Jason John Schwarz, North Carolina State University
Marge Skubic, University of Missouri, Columbia
Bill Sverdlik, Eastern Michigan University
Peter Stanchev, Kettering University
Krishnaprasad Thirunarayan, Wright State University
David Vineyard, Kettering University
Suzanne Westbrook, University of Arizona
Melissa Wiggins, Mississippi College
Zhiguang Xu, Valdosta State University.
The following reviewers have provided feedback on the chapters new to this
comprehensive edition:
Eric Matson, Wright State University
Tim Margush, University of Akron
Roxanne Canosa, Rochester Institute of Technology
Ivan Bajic, San Diego State University
Carolyn Miller, North Carolina State
Sunil Prabhakar, Purdue University
Weining Zhang, University of Texas, San Antonio
wu23399_fm.qxd 1/10/07 11:56 Page xxiv

Preface xxv
Personal Story
In September, 2001, I changed my name for personal reasons. Prof C. Thomas
Wu is now Prof Thomas W. Otani. To maintain continuity and not to confuse peo-
ple, we continue to publish the book under my former name. For those who
care to find out a little about my personal history can do so by visiting my web-
site (www.drcaffeine.com).
wu23399_fm.qxd 1/10/07 11:56 Page xxv

wu23399_fm.qxd 1/10/07 11:56 Page xxvi

O b j e c t i v e s
After you have read and studied this chapter,you should be able to
1
0
• State briefly a history of computers.
• Name and describe five major components of
the computer.
• Convert binary numbers to decimal numbers
and vice versa.
• State the difference between the low-level and
high-level programming languages.
Introduction to Computers
and Programming
Languages
wu23392_ch00.qxd 12/12/06 17:23 Page 1

2 Chapter 0 Introduction to Computers and Programming Languages
efore we embark on our study of computer programming, we will present some
background information on computers and programming languages in this optional
chapter. We provide a brief history of computers from the early days to present and
describe the components found in today’s computers. We also present a brief history
of programming languages from low-level machine languages to today’s object-
oriented languages.
0.1 A History of Computers
Humans have evolved from a primitive to a highly advanced society by continually
inventing tools. Stone tools, gunpowder, wheels, and other inventions have changed
the lives of humans dramatically. In recent history, the computer is arguably the
most important invention. In today’s highly advanced society, computers affect our
lives 24 hours a day: class schedules are formulated by computers, student records
are maintained by computers, exams are graded by computers, dorm security sys-
tems are monitored by computers, and numerous other functions that affect us are
controlled by computers.
Although the first true computer was invented in the 1940s, the concept of a
computer is actually more than 160 years old. Charles Babbage is credited with
inventing a precursor to the modern computer. In 1823 he received a grant from
the British government to build a mechanical device he called the Difference
Engine, intended for computing and printing mathematical tables. The device was
based on rotating wheels and was operated by a single crank. Unfortunately, the
technology of the time was not advanced enough to build the device. He ran into
difficulties and eventually abandoned the project.
But an even more grandiose scheme was already with him. In fact, one of the
reasons he gave up on the Difference Engine may have been to work on his new con-
cept for a better machine. He called his new device the Analytical Engine. This
device, too, was never built. His second device also was ahead of its time; the tech-
nology did not yet exist to make the device a reality. Although never built, the Ana-
lytical Engine was a remarkable achievement because its design was essentially
based on the same fundamental principles of the modern computer. One principle
that stands out was its programmability. With the Difference Engine, Babbage would
have been able to compute only mathematical tables, but with the Analytical Engine
he would have been able to compute any calculation by inputting instructions on
punch cards. The method of inputting programs to computers on punch cards was
actually adopted for real machines and was still in wide use as late as the 1970s.
The Analytical Engine was never built, but a demonstration program was
written by Ada Lovelace, a daughter of the poet Lord Byron. The programming lan-
guage Ada was named in honor of Lady Lovelace, the first computer programmer.
In the late 1930s John Atanasoff of Iowa State University, with his graduate
student Clifford Berry, built the prototype of the first automatic electronic calculator.
I n t r o d u c t i o n
B
Charles
Babbage
Difference
Engine
Analytical
Engine
Ada Lovelace
wu23392_ch00.qxd 12/12/06 17:23 Page 2

0.1 A History of Computers 3
One innovation of their machine was the use of binary numbers. (We discuss binary
numbers in Sec. 0.2.)At around the same time, HowardAiken of Harvard University
was working on the Automatic Sequence-Controlled Calculator, known more com-
monly as MARK I, with support from IBM and the U.S. Navy. MARK I was very
similar to the Analytical Engine in design and was described as “Babbage’s dream
come true.”
MARK I was an electromechanical computer based on relays. Mechanical
relays were not fast enough, and MARK I was quickly replaced by machines based
on electronic vacuum tubes. The first completely electronic computer, ENIAC I
(Electronic Numerical Integrator And Calculator), was built at the University of
Pennsylvania under the supervision of John W. Mauchly and J. Presper Eckert.
Their work was influenced by the work of John Atanasoff.
ENIAC I was programmed laboriously by plugging wires into a control
panel that resembled an old telephone switchboard. Programming took an enor-
mous amount of the engineers’ time, and even making a simple change to a pro-
gram was a time-consuming effort. While programming activities were going on,
the expensive computer sat idle. To improve its productivity, John von Neumann
of Princeton University proposed storing programs in the computer’s memory.
This stored program scheme not only improved computation speed but also al-
lowed far more flexible ways of writing programs. For example, because a pro-
gram is stored in the memory, the computer can change the program instructions
to alter the sequence of the execution, thereby making it possible to get different
results from a single program.
We characterized these early computers with vacuum tubes as first-generation
computers. Second-generation computers, with transistors replacing the vacuum
tubes, started appearing in the late 1950s. Improvements in memory devices also
increased processing speed further. In the early 1960s, transistors were replaced by
integrated circuits, and third-generation computers emerged. A single integrated
circuit of this period incorporated hundreds of transistors and made the construction
of minicomputers possible. Minicomputers are small enough to be placed on desk-
tops in individual offices and labs. The early computers, on the other hand, were so
huge that they easily occupied the whole basement of a large building.
Advancement of integrated circuits was phenomenal. Large-scale integrated
circuits, commonly known as computer chips or silicon chips, packed the power
equivalent to thousands of transistors and made the notion of a “computer on a sin-
gle chip” a reality. With large-scale integrated circuits, microcomputers emerged in
the mid-1970s. The machines we call personal computers today are descendants of
the microcomputers of the 1970s. The computer chips used in today’s personal
computers pack the power equivalent to several millions of transistors. Personal
computers are fourth-generation computers.
Early microcomputers were isolated, stand-alone machines. The word per-
sonal describes a machine as a personal device intended to be used by an individual.
However, it did not take long to realize there was a need to share computer resources.
For example, early microcomputers required a dedicated printer. Wouldn’t it make
more sense to have many computers share a single printer? Wouldn’t it also make
sense to share data among computers, instead of duplicating the same data on
MARK I
ENIAC I
stored program
generations of
computers
wu23392_ch00.qxd 12/12/06 17:23 Page 3

individual machines? Wouldn’t it be nice to send electronic messages between the
computers? The notion of networked computers arose to meet these needs.
Computers of all kinds are connected into a network. A network that connects
computers in a single building or in several nearby buildings is called a local-area
network or LAN. A network that connects geographically dispersed computers is
called a wide-area network or WAN. These individual networks can be connected
further to form interconnected networks called internets. The most famous internet
is simply called the Internet. The Internet makes the sharing of worldwide informa-
tion possible and easy. The hottest tool for viewing information on the Internet is a
Web browser. A Web browser allows you to experience multimedia information
consisting of text, audio, video, and other types of information. We will describe
how Java is related to the Internet and Web browsers in Section 0.4.
network
LAN
WAN
internet
1. Who was the first computer programmer?
2. Who designed the Difference Engine and Analytical Engine?
3. How many generations of computers are there?
0.2 Computer Architecture
A typical computer today has five basic components: RAM, CPU, storage devices,
I/O (input/output) devices, and communication devices. Figure 0.1 illustrates these
five components. Before we describe the components of a computer, we will explain
the binary numbering system used in a computer.
Binary Numbers
To understand the binary number system, let’s first review the decimal number sys-
tem in which we use 10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. To represent a number in
the decimal system, we use a sequence of one or more of these digits. The value that
each digit in the sequence represents depends on its position. For example, consider
the numbers 234 and 324. The digit 2 in the first number represents 200, whereas
the digit 2 in the second number represents 20. A position in a sequence has a
value that is an integral power of 10. The following diagram illustrates how the
If you want to learn more about the history of computing,there is a wealth of information
available on the Web.You can start your exploration from
www.yahoo.com/Computers_and_Internet/History
For more information on the pioneers of computers,visit
en.wikipedia.org/wiki/category:Computer_pioneers
wu23392_ch00.qxd 12/12/06 17:23 Page 4

values of positions are determined:
The value of a decimal number (represented as a sequence of digits) is the sum
of the digits, multiplied by their position values, as illustrated:
2 102
4 101
8 100
7 101
2 100 4 10 8 1 7 110
200 40 8 710 248.7
2
102
4
101
8
100
• 7
101
104
103
102
101
100
Decimal
Point
Position Values
101
102
• • •
• • •
103
•
Figure 0.1 A simplified view of an architecture for a typical computer.
Output
Devices
Communication
Devices
Input
Devices
RAM
CPU
Storage
Devices
Printer
(output device)
Monitor
(output device)
Main Unit (housing
CPU, RAM, storage
devices, and
communication
devices)
Mouse
(input device)
Keyboard
(input device)
wu23392_ch00.qxd 12/12/06 17:23 Page 5

In the decimal number system, we have 10 symbols, and the position values
are integral powers of 10. We say that 10 is the base or radix of the decimal number
system. The binary number system works the same as the decimal number system
but uses 2 as its base. The binary number system has two digits (0 and 1) called bits,
and position values are integral powers of 2. The following diagram illustrates how
the values of positions are determined in the binary system:
The value of a binary number (represented as a sequence of bits) is the sum of
the bits, multiplied by their position values, as illustrated:
1 22
0 21
1 20
1 21
1 4 0 2 1 1 1 12
4 0 1 12 5.5
So the binary number 101.1 is numerically equivalent to the decimal num-
ber 5.5. This illustration shows how to convert a given binary number to the
decimal equivalent. How about converting a given decimal number to its binary
equivalent?
The following steps show how to convert a decimal number (only the whole
numbers) to the equivalent binary number. The basic idea goes something like
this:
1. Divide the number by 2.
2. The remainder is the bit value of the 20
position.
3. Divide the quotient by 2.
position.
5. Divide the quotient by 2.
position.
7. Repeat the procedure until you cannot divide any further, that is, until the
quotient becomes 0.
1
22
0
21
1
20
• 1
21
24
23
• • •
• • •
22
21
20
Binary
Point
Position Values
•
21
22
23
base-2
numbers
binary number
bits
binary-to-
decimal
conversion
decimal-to-
binary
conversion
wu23392_ch00.qxd 12/12/06 17:23 Page 6

When you pay closer attention to the on/off switch on computers and other
electronic devices,you should notice an icon like this
This is a stylized representation of binary digits 0 and 1.
RAM
Random access memory or RAM is a repository for both program instructions and
data manipulated by the program during execution. RAM is divided into cells,
with each cell having a unique address. Typically, each cell consists of 4 bytes (B),
and a single byte (1 B) in turn consists of 8 bits. Each bit, which can be either on
or off, represents a single binary digit. RAM is measured by the number of bytes
it contains. For example, 128 kilobytes (KB) of RAM contains 128 1024
131,072 B because 1 KB is equal to 210
1024 B. Notice that 1 K is not equal to
103
, although 103
1000 is a close approximation to 210
1024. The first IBM
PC introduced in 1981 came with 16 KB of RAM, and the first Macintosh com-
puter introduced in 1984 came with 128 KB of RAM. In contrast, a typical PC
today has anywhere from 128 MB to 512 MB of RAM. Given that 1 MB is equal
to 1024 KB, we know that 256 MB means 256 1024 KB 262,144 KB
262,144 1024 B 268,435,456 B.
RAM
byte
The following diagram illustrates the conversion of decimal number 25.
Division Division Division Division Division
#5 #4 #3 #2 #1
24
23
22
21
20
16 8 0 0 1 25
The binary system is more suitable for computers than the decimal system be-
cause it is far easier to design an electrical device that can distinguish two states
(bits 0 and 1) than 10 states (digits 0 through 9). For example, we can represent 1 by
turning the switch on and 0 by turning the switch off. In a real computer, 0 is repre-
sented by electrical voltage below a certain level and 1 by electrical voltage at or
above this level.
12
21
2
5
1

24
1
6
21
1
2
1

12
0
3
21
6
1

6
0
1
21
3
1

2
1
0
21
1
1

0
1
wu23392_ch00.qxd 12/12/06 17:23 Page 7

CPU
The central processing unit or CPU is the brain of a computer. The CPU is the com-
ponent that executes program instructions by fetching an instruction (stored in
RAM), executing it, fetching the next instruction, executing it, and so on until it en-
counters an instruction to stop. The CPU contains a small number of registers, which
are high-speed devices for storing data or instructions temporarily. The CPU also
contains the arithmetic-logic unit (ALU), which performs arithmetic operations such
as addition and subtraction and logical operations such as comparing two numbers.
CPUs are characterized by their clock speeds. For example, in the Intel
Pentium 200, the CPU has a clock speed of 200 megahertz (MHz). The hertz is a
unit of frequency equal to 1 cycle per second. A cycle is a period of time between
two on states or off states. So 200 MHz equals 200,000,000 cycles per second. The
fastest CPU for commercially available personal computers was around 200 MHz
in 1997 when the first edition of this textbook was published. But by the beginning
of 1998, many vendors started selling 300-MHz machines. And in a mere 6 months,
by the middle of 1998, the top-of-the-line personal computers were 400-MHz ma-
chines. As of this writing in late 2002, we see computers with 2.0-GHz (2000-MHz)
CPU being advertised and sold. The increase of the CPU speed in the last two
decades is truly astonishing. The clock speed of the Intel 8080, the CPU introduced
in 1974 that started the PC revolution, was a mere 2 MHz. In contrast, the clock
speed of the Intel Pentium 4 introduced in 2001 was 2 GHz (2000 MHz). Table 0.1
lists some of the Intel processors.
I/O Devices
Input/output or I/O devices allow communication between the user and the CPU.
Input devices such as keyboards and mice are used to enter data, programs, and
commands in the CPU. Output devices such as monitors and printers are used to
display or print information. Other I/O devices include scanners, bar code readers,
magnetic strip readers, digital video cameras, and musical instrument digital inter-
face (MIDI) devices.
Storage Devices
Storage devices such as disk and tape drives are used to store data and programs. Sec-
ondary storage devices are called nonvolatile memory, while RAM is called volatile
memory. Volatile means the data stored in a device will be lost when the power to the
device is turned off. Being nonvolatile and much cheaper than RAM, secondary stor-
age is an ideal medium for permanent storage of large volumes of data. A secondary
storage device cannot replace RAM, though, because secondary storage is far slower
in data access (getting data out and writing data in) compared to RAM.
The most common storage device today for personal computers is a disk
drive. There are two kinds of disks: hard and floppy (also known as diskettes). Hard
disks provide much faster performance and larger capacity, but are normally not re-
movable; that is, a single hard disk is permanently attached to a disk drive. Floppy
disks, on the other hand, are removable, but their performance is far slower and
their capacity far smaller than those of hard disks. As the standard floppy disks can
CPU
register
clock speed
I/O devices
nonvolatile and
volatile
memory
wu23392_ch00.qxd 12/12/06 17:23 Page 8

store only up to approximately 1.44 MB, they are becoming less useful in today’s
world of multimegabyte image and sound files. They are fast becoming obsolete,
and hardly anybody uses them anymore. Removable storage media with much
higher capacity such as zip disks (capable of holding 100 to 250 MB of data) re-
placed floppy disks in late 1990s. Computer technology moves so quickly that zip
disks themselves are already becoming obsolete. The most common form of
portable storage medium today (2006) is a compact USB flash drive, whose capac-
ity ranges from 125 MB to 16 GB.
Hard disks can store a huge amount of data, typically ranging from 20 GB
(gigabyte; 1 GB 1024 MB) to 80 GB for a standard desktop PC in 2002. Portable
and removable hard disk drives, with performance and capacity that rival those of
nonremovable hard disks, are also available, but their use is not widespread.
Compact disks (CDs) are very popular today for storing massive amounts of
data, approximately 700 MB. Many software packages we buy today—computer
Table
Table 0.1
A table of Intel processors.For some CPUs,several types with different
clock speeds are possible.In such case,only the fastest clock speed is
shown.For more information on Intel CPUs,visit http://www.intel.com.
Date Clock Speed
CPU Introduced (MHz)
4004 11/15/71 0.108
8008 4/1/72 0.200
1970s 8080 4/1/74 2
8088 6/1/79 8
80286 2/1/82 12
1980s 80386SX 6/16/88 16
80486DX 4/10/89 25
Pentium 3/22/93 66
Pentium Pro 11/1/95 200
1990s Pentium II 5/7/97 300
Pentium II Xeon 6/29/98 400
Pentium III 10/25/99 733
Xeon 9/25/01 2000
2000s
Pentium 4 4/27/01 2000
Itanium 2 7/8/02 1000
Pentium 4 Extreme 2/2/04 3400
Edition
Core 2 Extreme 7/27/06 3200
wu23392_ch00.qxd 12/12/06 17:23 Page 9

games, word processors, and others—come with a single CD. Before the CD became
apopularstoragedeviceforcomputers,somesoftwarecamewithmorethan20floppy
diskettes. Because of the massive storage capacity of the CD, most computer vendors
eliminated printed manuals altogether by putting the manuals on the CD.
Communication Devices
A communication device connects the personal computer to an internet. The most
common communication device for computers at home and in small offices is the
modem. A modem, which stands for modulator-demodulator, is a device that con-
verts analog signals to digital and digital signals to analog. By using a modem, a
computer can send to and receive data from another computer over the phone line.
The most critical characteristic of a modem is its transmission speed, which is mea-
sured in bits per second (bps). A typical speed for a modem is 56,000 bps, com-
monly called a 56K modem. Under an ideal condition (no line noise or congestion),
a 56K modem can transfer a 1 MB file in about 21
⁄2 minutes. Frequently, though, the
actual transfer rate is much lower than the possible maximum. So-called DSL and
cable modems are not truly modems because they transfer data strictly in digital
mode, which allows for much faster connection speeds of 144K or above. High-
speed satellite connection to the Internet is also available today.
A communication device for connecting a computer to a LAN is a network
interface card (NIC). A NIC can transfer data at a much faster rate than the fastest
modem. For instance, a type of NIC called 10BaseT can transfer data at the rate
of 10 Mbps over the network. Traditional networks are connected, or wired, by the
cables. Increasingly, networks are connected wirelessly, where data are carried over
radio waves. Wireless networking is called WiFi or 802.11 networking. Today you
will find wireless networking almost universally available at airports and hotels.
communication
device
1. Name five major components of a computer.
2. What is the difference between volatile and nonvolatile memory?
3. What does the acronym CPU stand for?
4. How many bytes does the 64 KB RAM have?
5. Which device connects a computer to the Internet using a phone line?
Today we see more and more companies are even eliminating CDs and promoting
“boxless”online distribution of software.With this scheme,we go to their websites
and download the software,after paying for it with our credit card.Maybe someday
we may be able to buy textbooks in the same manner and stop carrying 20 lb of
dead trees in our backpacks.
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0.3 Programming Languages
Programming languages are broadly classified into three levels: machine languages,
assembly languages, and high-level languages. Machine language is the only pro-
gramming language the CPU understands. Each type of CPU has its own machine
language. For example, the Intel Pentium and Motorola PowerPC understand differ-
ent machine languages. Machine-language instructions are binary-coded and very
low level—one machine instruction may transfer the contents of one memory loca-
tion into a CPU register or add numbers in two registers. Thus we must provide many
machine-language instructions to accomplish a simple task such as finding the aver-
age of 20 numbers.Aprogram written in machine language might look like this:
10110011 00011001
01111010 11010001 10010100
10011111 00011001
01011100 11010001 10010000
10111011 11010001 10010110
One level above machine language is assembly language, which allows
“higher-level” symbolic programming. Instead of writing programs as a sequence
of bits, assembly language allows programmers to write programs by using sym-
bolic operation codes. For example, instead of 10110011, we use MV to move the
contents of a memory cell into a register. We also can use symbolic, or mnemonic,
names for registers and memory cells. A program written in assembly language
might look like this:
MV 0, SUM
MV NUM, AC
ADD SUM, AC
STO SUM, TOT
Since programs written in assembly language are not recognized by the CPU,
we use an assembler to translate programs written in assembly language into
machine-language equivalents. Compared to writing programs in machine lan-
guage, writing programs in assembly language is much faster, but not fast enough
for writing complex programs.
High-level languages were developed to enable programmers to write pro-
grams faster than when using assembly languages. For example, FORTRAN
(FORmula TRANslator), a programming language intended for mathematical com-
putation, allows programmers to express numerical equations directly as
X = (Y + Z) / 2
COBOL (COmmon Business-Oriented Language) is a programming language in-
tended for business data processing applications. FORTRAN and COBOL were de-
veloped in the late 1950s and early 1960s and are still in use. BASIC (Beginners
All-purpose Symbolic Instructional Code) was developed specifically as an easy
language for students to learn and use. BASIC was the first high-level language
0.3 Programming Languages 11
machine
language
machine code
assembly code
assembler
high-level code
high-level
languages
assembly
language
wu23392_ch00.qxd 12/12/06 17:23 Page 11

available for microcomputers. Another famous high-level language is Pascal, which
was designed as an academic language. Since programs written in a high-level lan-
guage are not recognized by the CPU, we must use a compiler to translate them to
assembly language equivalents.
The programming language C was developed in the early 1970s at ATT Bell
Labs. The C++ programming language was developed as a successor of C in the
early 1980s to add support for object-oriented programming. Object-oriented pro-
gramming is a style of programming gaining wider acceptance today. Although the
concept of object-oriented programming is old (the first object-oriented program-
ming language, Simula, was developed in the late 1960s), its significance wasn’t
realized until the early 1980s. Smalltalk, developed at Xerox PARC, is another
well-known object-oriented programming language. The programming language
we use in this book is Java, the newest object-oriented programming language,
developed at Sun Microsystems.
0.4 Java
Java isanewobject-orientedlanguagethatisreceivingwideattentionfrombothindus-
try and academia. Java was developed by James Gosling and his team at Sun Microsys-
tems in California. The language was based on C and C++ and was originally intended
for writing programs that control consumer appliances such as toasters, microwave
ovens,andothers.ThelanguagewasfirstcalledOak,namedaftertheoaktreeoutsideof
Gosling’s office, but the name was already taken, so the team renamed it Java.
Java is often described as a Web programming language because of its use in
writing programs called applets that run within a Web browser. That is, you need a
Web browser to execute Java applets. Applets allow more dynamic and flexible dis-
semination of information on the Internet, and this feature alone makes Java an at-
tractive language to learn. However, we are not limited to writing applets in Java.
We can write Java applications also. A Java application is a complete stand-alone
program that does not require a Web browser. A Java application is analogous to a
program we write in other programming languages. In this book, we focus on Java
applications because our objective is to teach the fundamentals of object-oriented
programming that are applicable to all object-oriented programming languages.
We chose Java for this textbook mainly for its clean design. The language de-
signers of Java took a minimalist approach; they included only features that are in-
dispensable and eliminated features that they considered excessive or redundant.
This minimalist approach makes Java a much easier language to learn than other
object-oriented programming languages. Java is an ideal vehicle for teaching the
fundamentals of object-oriented programming.
compiler
Java
applet
application
• Charles Babbage invented the Difference Engine and Analytical Engine,
precursors to the modern computer.
• Ada Lovelace is considered the first computer programmer.
• The first two modern computers were MARK I and ENIAC I.
S u m m a r y
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• John von Neumann invented the stored-program approach of executing
programs.
• Computers are connected into a network. Interconnected networks are
called internets.
• Binary numbers are used in computers.
• A typical computer consists of five components: RAM, CPU, storage
devices, I/O devices, and communication devices.
• There are three levels of programming languages: machine, assembly, and
high-level.
• Java is one of the newest high-level programming languages in use today.
This textbook teaches how to program using Java.
Exercises 13
K e y C o n c e p t s
network
LAN
WAN
internets and Internet
CPU
RAM
I/O devices
communication devices
binary numbers
binary-to-decimal conversion
machine language
assembly language
assembler
high-level language
compiler
Java
E x e r c i s e s
1. Visit your school’s computer lab or a computer store, and identify the
different components of the computers you see. Do you notice any unique
input or output devices?
2. Visit your school’s computer lab and find out the CPU speed, RAM size, and
hard disk capacity of its computers.
3. Convert these binary numbers to decimal numbers.
a. 1010
b. 110011
c. 110.01
d. 111111
4. Convert these decimal numbers to binary numbers.
a. 35
b. 125
c. 567
d. 98
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5. What is the maximum decimal number you can represent in 4 bits? 16 bits?
N bits?
6. If a computer has 128 MB of RAM, how many bytes are there?
7. How do high-level programming languages differ from low-level
programming languages?
8. Consider a hypothetical programming language called Kona. Using Kona,
you can write a program to compute and print out the sum of 20 integers
entered by the user:
let sum = 0;
repeat 20 times [
let X = next input;
add X to sum;
]
printout sum;
Is Kona a high-level language? Why or why not?
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Introduction to Object-Oriented
Programming and Software
Development
O b j e c t i v e s
After you have read and studied this chapter,you should be able to
• Name the basic components of object-
oriented programming.
• Differentiate classes and objects.
• Differentiate class and instance
methods.
• Differentiate class and instance data
values.
• Draw program diagrams using icons for
classes,objects,and other components of
object-oriented programming.
• Describe the significance of inheritance in
object-oriented programs.
• Name and explain the stages of the software
life cycle.
15
1
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efore we begin to write actual programs, we need to introduce a few basic concepts
of object-oriented programming (OOP), the style of programming we teach in this
book. The purpose of this chapter is to give you a feel for object-oriented program-
ming and to introduce a conceptual foundation of object-oriented programming.You
may want to refer to this chapter as you progress through the book. What we discuss
in the next four sections is independent of any particular programming language.
16 Chapter 1 Introduction to Object-Oriented Programming and Software Development
I n t r o d u c t i o n
B
object-
oriented
programming
object
Those of you who have some experience in programming, whether object-
oriented or non-object-oriented,will probably find many similarities between Java
and the programming languages you already know.This similarity may accelerate
your learning process, but in many cases what seems to be similar at first may
turn out to be quite different. So please do not jump to any conclusions about
similarity prematurely.
Another purpose of this chapter is to introduce the software development
process. To be able to write programs, knowledge of the components of object-
oriented programs is not enough. We must learn the process of developing pro-
grams. We will present a brief introduction to the software development process in
this chapter.
1.1 Classes and Objects
The two most important concepts in object-oriented programming are the class
and the object. In the broadest term, an object is a thing, both tangible and intangi-
ble, that we can imagine. A program written in object-oriented style will consist
of interacting objects. For a program to keep track of student residents of a college
dormitory, we may have many Student, Room, and Floor objects. For another pro-
gram to keep track of customers and inventory for a bicycle shop, we may have
Customer, Bicycle, and many other types of objects. An object is comprised of data
and operations that manipulate these data. For example, a Student object may con-
sist of data such as name, gender, birth date, home address, phone number, and age
and operations for assigning and changing these data values. We will use the nota-
tion shown in Figure 1.1 throughout the book to represent an object. The notation
we used in the book is based on the industry standard notation called UML, which
stands for Unified Modeling Language. In some of the illustrations, we relax the
rules of UML slightly for pedagogy.
Almost all nontrivial programs will have many objects of the same type.
For example, in the bicycle shop program we expect to see many Bicycle and other
objects. Figure 1.2 shows two Bicycle objects with the names Moto-1 and Moto-2
and one Customer object with the name Jon Java.
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Inside a program we write instructions to create objects. For the computer to
be able to create an object, we must provide a definition, called a class. A class is a
kind of mold or template that dictates what objects can and cannot do. An object
is called an instance of a class. An object is an instance of exactly one class. An
instance of a class belongs to the class. The two Bicycle objects Moto-1 and Moto-2
are instances of the Bicycle class. Once a class is defined, we can create as many
instances of the class as a program requires.
1.1 Classes and Objects 17
class
instance
Object name
We use a rectangle to
represent an object and
place the underlined
name of the object
inside the rectangle.
Example: account1
This is an object
named account1.
Figure 1.1 A graphical representation of an object.
Jon Java : Customer
Moto-2 : Bicycle
Moto-1 : Bicycle
An object name is followed
by the class name.
Figure 1.2 Two Bicycle objects with the names Moto-1 and Moto-2 and one Customer object with the name
Jon Java.
A class must be defined before you can create an instance (object) of the class.
Figure 1.3 shows a diagram that we will use throughout the book to represent
a class.
1. Draw an object diagram for a Person class and two Person objects, Ms. Latte
and Mr. Espresso.
2. What must be defined before you can create an object?
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1.2 Messages and Methods
In writing object-oriented programs we must first define classes, and while the pro-
gram is running, we use the classes and objects from these classes to accomplish
tasks. A task can range from adding two numbers, to computing an interest payment
for a college loan, to calculating the reentry angle of a space shuttle. To instruct a
class or an object to perform a task, we send a message to it. For example, we send
a message deposit to an Account object to deposit $100.
For a class or an object to process the message, it must be programmed ac-
cordingly. You cannot just send a message to any class or object. You can send a
message only to the classes and objects that understand the message you send. For
a class or an object to process the message it receives, it must possess a matching
method, which is a sequence of instructions that a class or an object follows to
perform a task. A method defined for a class is called a class method, and a method
defined for an object is an instance method.
Example:
We use a rectangle to
represent a class with
its name appearing
inside the rectangle.
Class Name
Notice the name of a
class is not underlined
while the name of an
object is.
Account
Figure 1.3 A graphical representation of a class.
Many beginning programmers may not see the distinction between the class and object as
clearly as the more experienced programmers do.It may be helpful to compare the class
and object to a woodcut and the prints produced from the woodcut.A woodcut is a block
of wood engraved with a design for printing.Once you have a woodcut,you can make as
many prints as you wish.Similarly,once you have a class,you can make as many objects
from the class.Also,just as you cannot make prints without having a woodcut,you cannot
create an object without first defining a class.For sample prints by the 19th-century
Japanese artist Hiroshige,visit
http://www.ibiblio.org/wm/paint/auth/hiroshige/
Another helpful analogy is a robot factory.A factory is a class,and the robots
produced from the factory are the objects of the class.To create robots (instance),we
need the factory (class) first.Those interested in mobile robots can visit
http://www.ai.mit.edu/projects/mobile-robots/robots.html
message
method
class and
instance
methods
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Let’s look at an example of an instance method first. Suppose a method called
walk is defined for a Robot object and instructs the robot to walk a designated dis-
tance. With this method defined, we can send the message walk to a Robot object,
along with the distance to be walked. A value we pass to an object is called an
argument of a message. Notice that the name of the message we send to an object or
a class must be the same as the method’s name. In Figure 1.4 we represent the send-
ing of a message.
The diagram in Figure 1.4 illustrates one-way communication; that is, an
object carries out the requested operation (it walks the designated distance) but
does not respond to the message sender. In many situations we need a reply in
which an object responds by returning a value to the message sender. For exam-
ple, suppose we want to know the distance from a robot to its nearest obstacle.
The designer of a robot may include a method getObstacleDistance that returns
the desired value. The diagram in Figure 1.5 shows a method that returns a value
to the message sender. Instead of returning a numerical value, a method can re-
port back the status of the requested operation. For example, a method walk can
be defined to return the status success/fail to indicate whether the specified
distance was covered successfully or not (e.g., it fails when the robot bumps into
an obstacle).
Now let’s look at an example of class methods. The class method getMaxi-
mumSpeed shown in Figure 1.6 returns the maximum possible speed of all Robot
objects. A method such as getMaximumSpeed that deals with collective information
about the instances of a class is usually defined as a class method. So we define an
instance method for a task that pertains to an individual instance and a class method
for a task that pertains to all instances.
1.2 Messages and Methods 19
argument
walk(25)
fido : Robot
Message walk with
the argument 25.
Figure 1.4 Sending the message walk to a Robot object.
getObstacleDistance( )
distance
fido : Robot
This shows that we are not
sending any argument.
This shows the value
distance is returned as
a response to the message.
Figure 1.5 The result distance is returned to the sender of the message.
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getMaximumSpeed( )
maximum speed
Robot
Figure 1.6 The maximum possible speed of all Robot objects is returned by the class method
getMaximumSpeed.
1. Draw an object diagram of an Account object with instance methods deposit
and withdraw.
2. Is the getObstacleDistance method an instance or a class method?
1.3 Class and Instance Data Values
Suppose the method deposit of an Account object instructs the object to add a given
amount to the current balance. Where does the object keep the current balance?
Remember that an object is comprised of data values and methods. Analogous to
defining class and instance methods, we can define class and instance data values.
For example, we define an instance data value current balance for Account objects
to record the current balance. Figure 1.7 shows three Account objects with their
data values current balance. Notice that they all have the same data value current
balance.All instances of the same class will possess the same set of data values. The
actual dollar amounts for current balance, as the diagram illustrates, differ from one
instance to another. Items such as opening balance and account number are other
possible instance data values for Account objects.
A class data value is used to represent information shared by all instances or to
represent collective information about the instances. For example, if every account
must maintain a minimum balance of, say, $100, we can define a class data value
minimum balance. An instance can access the class data values of the class to which
it belongs, so every Account object can access the class data value minimum balance.
Jill’s : Account
1304.98
current balance
Jack’s : Account
354.00
current balance
John’s : Account
908.55
current balance
Figure 1.7 Three Account objects possess the same data value current balance, but the actual dollar
amounts differ.
instance data
value
class data value
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Figure 1.8 shows how we represent a class data value. Notice that we underline the
class data value. Because the objects of a class are underlined, and the class data val-
ues are accessible to all objects of the class, we likewise underline the class data
value to show this relationship. Data values are also called data members because
they belong to a class or instance of the class.
To appreciate the significance of a class data value, let’s see what happens if
we represent minimum balance as an instance data value. Figure 1.9 shows three
Account objects having different dollar amounts for the current balance but the
same dollar amount for the minimum balance. Obviously, this duplication of mini-
mum balance is redundant and wastes space. Consider, for example, what happens
if the bank raises the minimum balance to $200. If there are 100 Account objects,
then all 100 copies of minimum balance must be updated. We can avoid this by
defining minimum balance as a class data value. Figure 1.10 shows another exam-
ple where the opening and closing times are shared by all cafeterias on campus.
There are two types of data values: those that can change over time and those
that cannot. A data value that can change is called a variable, and one that cannot
1.3 Class and Instance Data Values 21
John’s : Account
908.55
current balance
Jill’s : Account
1304.98
current balance
Account
minimum balance
100.00
Jack’s : Account
354.00
current balance
Notice the class data value is
underlined to show the fact that this
value is accessible to individual
objects, which are underlined.
Figure1.8 Three Account objects sharing information (minimumbalance $100) stored as a class data value.
data member
variable
John’s : Account
908.55
current balance
minimum balance
100.00
Jill’s : Account
1304.98
current balance
minimum balance
100.00
Jack’s : Account
354.00
current balance
minimum balance
100.00
Figure1.9 ThreeAccountobjectsduplicatinginformation(minimumbalance $100)ininstancedatavalues.
wu23399_ch01.qxd 12/12/06 17:24 Page 21

change is a constant. Figure 1.11 illustrates how we represent and distinguish be-
tween variables and constants. We use the keyword frozen for constants to indicate
that they cannot change. Notice that we now have four kinds of data values: class
variables, class constants, instance variables, and instance constants.
Union : Cafeteria
1917.34
revenue
West : Cafeteria
2306.99
revenue
QuikBite : Cafeteria
430.75
revenue
Cafeteria
opens
0600
closes
2100
Figure 1.10 Three Cafeteria objects sharing the same opening and closing times,stored as class data values.
John’s : Account
908.55
current balance
opening balance
{frozen}
246.00
Jill’s : Account
1304.98
current balance
opening balance
{frozen}
50.00
Account
100.00
minimum balance
account prefix
{frozen}
6427
Jack’s : Account
354.00
current balance
opening balance
{frozen}
100.00
We assume this number is
a prefix to the account
number of all accounts, and
the prefix never changes.
This keyword indicates
the value is locked and
cannot be changed.
Figure 1.11 Graphical representations for four types of data values:class variable,class constant,instance
variable,and instance constant.
constant
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1.4 Inheritance
When we used the Account class and its instances to illustrate object-oriented con-
cepts, some of you were probably thinking about checking accounts, while others
may have been thinking about savings accounts. We did not distinguish between the
two in the examples. But when we look at the problem a little more carefully, we
will realize that in fact these two types of accounts are different, even though they
share many features.
In general, using only a single class to model two or more entities that are
similar but different is not good design. In object-oriented programming, we use a
mechanism called inheritance to design two or more entities that are different but
share many common features. First we define a class that contains the common fea-
tures of the entities. Then we define classes as an extension of the common class
inheriting everything from the common class. We call the common class the
superclass and all classes that inherit from it subclasses. We also call the superclass
an ancestor and the subclass a descendant. Other names for superclass and subclass
are base class and derived class, respectively. For the bank example, we can define
a superclass Account and then define Savings and Checking as subclasses of
Account. We represent the superclass and its subclasses as shown in Figure 1.12.
Notice that we draw arrows from each subclass to its superclass because a subclass
can refer to items defined in its superclass, but not vice versa.
Inheritance is not limited to one level. A subclass can be a superclass of other
classes, forming an inheritance hierarchy. Consider the example shown in
Figure 1.13. Inheritance is very powerful, and if it is used properly, we can develop
1.4 Inheritance 23
1. What is the difference between a constant and a variable?
2. Draw an object diagram of a Person object with the three instance variables
name, age, and gender.
Account
Savings Checking
Figure 1.12 A superclass Account and its subclasses Savings and Checking.
inheritance
superclass and
subclass
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complex programs very efficiently and elegantly. The flip side of using a very pow-
erful tool is that if we do not use it correctly, we could end up in a far worse situation
than if we did not use it. We will be seeing many examples of inheritance through-
out this book. In Chapter 2, for example, we will introduce many classes that come
with the Java system. Most of these classes are defined using inheritance. We will
provide an in-depth discussion of inheritance and related topics in Chapter 13.
Student
Law
Doctoral
Masters
Graduate Undergraduate
Commuting Resident
Figure 1.13 An example of inheritance hierarchy among different types of students.
1. If Class A inherits from Class B, which is a superclass? Which is a subclass?
2. Draw a diagram that shows Class A is inheriting from Class B.
3. What are the other names for superclass and subclass?
4. If we have Animal, Insect, and Mammal classes, which one will be a
superclass?
5. Model different types of vehicles, using inheritance. Include Vehicle,
Automobile, Motorcycle, Sports Car, Sedan, and Bicycle.
1.5 Software Engineering and Software Life Cycle
When we say computer programming, we are referring not only to writing Java
commands, but also to a whole process of software development. Knowing a pro-
gramming language alone is not enough to become a proficient software developer.
wu23399_ch01.qxd 12/12/06 17:24 Page 24

Other documents randomly have
different content

Anaxagoras made no distinction between νοῦς and ψυχή.
Compare Plato, Kratylus, p. 400 A.
161 Anaxag. Fr. 8, and Schaubach’s Comm. p. 112-116.
“Mens erat id, quod movebat molem homœomeriarum:
hâc ratione, per hunc motum à mente excitatum, secretio
facta est.… Materiæ autem propriæ insunt vires: proprio
suo pondere hæc, quæ mentis vi mota et secreta sunt,
feruntur in eum locum, quo nunc sunt.”
Compare Alexand. Aphrod. ap. Scholia ad Aristot.
Physic. ii. p. 194, a. (Schol. p. 348 a. Brandis); Marbach,
Lehrbuch der Gesch. Philos. s. 54, note 2, p. 82; Preller,
Hist. Phil. ex Font. Loc. Contexta, s. 53, with his
comment.
162 Plato, Phædo, c. 107, 108, p. 98; Plato, De Legg.
xii. p. 967 B; Aristot. Metaphys. A. 4, p. 985, b. 18; Plato,
Timæus, 34 A. 88 E.
163 Aristoph. Nub. 380, 828. αἰθέριος Δῖνος — Δῖνος
βασιλεύει, τὸν Δί’ ἐξεληλακώς — the sting of which
applies to Anaxagoras and his doctrines.
Anaxagoras δίνους τινὰς ἀνοήτους ἀναζωγραφῶν, σὺν
τῇ τοῦ νοῦ ἀπραξίᾳ καὶ ἀνοίᾳ (Clemens. Alexandrin.
Stromat. ii. p. 365).
To move (in the active sense, i.e. to cause movement
in) and to know, are the two attributes of the
Anaxagorean Νοῦς (Aristotel. De Animâ, i. 2, p. 405, a.
18).

Plato and Aristotle blame
Anaxagoras for deserting
his own theory.
This we learn from Plato and Aristotle,
who blame Anaxagoras for inconsistency
in deserting his own hypothesis, and in
invoking explanations from physical
agencies, to the neglect of Nous and its supposed optimising purposes.
But Anaxagoras, as far as we can judge by his remaining fragments,
seems not to have committed any such inconsistency. He did not
proclaim his Nous to be a powerful extra-cosmical Architect, like the
Demiurgus of Plato — nor an intra-cosmical, immanent, undeliberating
instinct (such as Aristotle calls Nature), tending towards the production
and renewal of regular forms and conjunctions, yet operating along
with other agencies which produced concomitants irregular,
unpredictable, often even obstructive and monstrous. Anaxagoras
appears to conceive his Nous as one among numerous other real
agents in Nature, material like the rest, yet differing from the rest as
being powerful, simple, and pure from all mixture,164 as being endued
with universal cognizance, as being the earliest to act in point of time,
and as furnishing the primary condition to the activity of the rest by
setting on foot the cosmical rotation. The Homœomeries are coeternal
with, if not anterior to, Nous. They have laws and properties of their
own, which they follow, when once liberated, without waiting for the
dictation of Nous. What they do is known by, but not ordered by,
Nous.165 It is therefore no inconsistency in Anaxagoras that he assigns
to mind one distinct and peculiar agency, but nothing more; and that
when trying to explain the variety of phenomena he makes reference to
other physical agencies, as the case seems to require.166
164 Anaxagoras, Fr. 8, p. 100, Schaub.
ἐστὶ γὰρ λεπτότατόν τε πάντων χρημάτων, c.

Astronomy and physics of
Anaxagoras.
This means, not that νοῦς was unextended or
immaterial, but that it was thinner or more subtle than
either fire or air. Herakleitus regarded τὸ περιέχον as
λογικὸν καὶ φρενῆρες. Diogenes of Apollonia considered
air as endued with cognition, and as imparting cognition
by being inhaled. Compare Plutarch, De Placit. Philos. iv.
3.
I cannot think, with Brücker (Hist. Philosop. part ii. b.
ii. De Sectâ Ionicâ, p. 504, ed. 2nd), and with
Tennemann, Ges. Ph. i. 8, p. 312, that Anaxagoras was
“primus qui Dei ideam inter Græcos à materialitate quasi
purificavit,” c. I agree rather with Zeller (Philos. der
Griech. i. p. 680-683, ed. 2nd), that the Anaxagorean
Nous is not conceived as having either immateriality or
personality.
165 Simplikius, in Physic. Aristot. p. 73. καὶ Ἀναξαγόρας
δὲ τὸν νοῦν ἐάσας, ὥς φησιν Εὔδημος, καὶ αὐτοματίζων
τὰ πολλὰ συνίστησιν.
166 Diogen. Laert. ii. 8. Νοῦν … ἀρχὴν κινήσεως.
Brücker, Hist. Philos. ut supra. “Scilicet, semel inducto
in materiam à mente motu, sufficere putavit Anaxagoras,
juxta leges naturæ motûsque, rerum ortum describere.”
In describing the formation of the
Kosmos, Anaxagoras supposed that, as a
consequence of the rotation initiated by
mind, the primitive chaos broke up. “The Dense, Wet, Cold, Dark,
Heavy, came together into the place where now Earth is: Hot, Dry,
Bare, Light, Bright, departed to the exterior region of the revolving
Æther.”167 In such separation each followed its spontaneous and

inherent tendency. Water was disengaged from air and clouds, earth
from water: earth was still farther consolidated into stones by cold.168
Earth remained stationary in the centre, while fire and air were borne
round it by the force and violence of the rotatory movement. The
celestial bodies — Sun, Moon, and Stars — were solid bodies analogous
to the earth, either caught originally in the whirl of the rotatory
movement, or torn from the substance of the earth and carried away
into the outer region of rotation.169 They were rendered hot and
luminous by the fiery fluid in the rapid whirl of which they were hurried
along. The Sun was a stone thus made red-hot, larger than
Peloponnesus: the Moon was of earthy matter, nearer to the Earth,
deriving its light from the Sun, and including not merely plains and
mountains, but also cities and inhabitants.170 Of the planetary
movements, apart from the diurnal rotation of the celestial sphere,
Anaxagoras took no notice.171 He explained the periodical changes in
the apparent course of the sun and moon by resistances which they
encountered, the former from accumulated and condensed air, the
latter from the cold.172 Like Anaximenes and Demokritus, Anaxagoras
conceived the Earth as flat, round in the surface, and not deep, resting
on and supported by the air beneath it. Originally (he thought) the
earth was horizontal, with the axis of celestial rotation perpendicular,
and the north pole at the zenith, so that this rotation was then lateral,
like that of a dome or roof; it was moreover equable and unchanging
with reference to every part of the plane of the earth’s upper surface,
and distributed light and heat equally to every part. But after a certain
time the Earth tilted over of its own accord to the south, thus lowering
its southern half, raising the northern half, and causing the celestial
rotation to appear oblique.173
167 Anaxag. Fr. 19, p. 131, Schaub.; compare Fr. 6, p.
97; Diogen. Laert. ii. 8.

His geology, meteorology,
physiology.
168 Anaxag. Fr. 20, p. 133, Schau.
169 See the curious passage in Plutarch, Lysander 12,
and Plato, Legg. xii. p. 967 B; Diogen. Laert. ii. 12;
Plutarch, Placit. Philos. ii. 13.
170 Plato, Kratylus, p. 409 A; Plato, Apol. Sok. c. 14;
Xenophon, Memorab. iv. 7.
171 Schaubach, ad Anax. Fr. p. 165.
172 Plutarch, Placit. Philosoph. ii. 23.
173 Diogenes Laert. ii. 9. τὰ δ’ ἄστρα κατ’ ἀρχὰς
θολοειδῶς ἐνεχθῆναι, ὥστε κατὰ κορυφὴν τῆς γῆς τὸν
ἀεὶ φαινόμενον εἶναι πόλον, ὕστερον δὲ τὴν (γῆν)
ἔγκλισιν λαβεῖν. Plutarch, Placit. Phil. ii. 8.
Besides these doctrines respecting the
great cosmical bodies, Anaxagoras gave
explanations of many among the striking
phenomena in geology and meteorology — the sea, rivers,
earthquakes, hurricanes, hail, snow, c.174 He treated also of animals
and plants — their primary origin, and the manner of their
propagation.175 He thought that animals were originally produced by
the hot and moist earth; but that being once produced, the breeds
were continued by propagation. The seeds of plants he supposed to
have been originally contained in the air, from whence they fell down to
the warm and moist earth, where they took root and sprung up.176 He
believed that all plants, as well as all animals, had a certain measure of
intelligence and sentiment, differing not in kind but only in degree from
the intelligence and sentiment of men; whose superiority of intelligence
was determined, to a great extent, by their possession of hands.177 He
explained sensation by the action of unlike upon unlike (contrary to

Empedokles, who referred it to the action of like upon like),178 applying
this doctrine to the explanation of the five senses separately. But he
pronounced the senses to be sadly obscure and insufficient as means of
knowledge. Apparently, however, he did not discard their testimony, nor
assume any other means of knowledge independent of it, but supposed
a concomitant and controlling effect of intelligence as indispensable to
compare and judge between the facts of sense when they appeared
contradictory.179 On this point, however, it is difficult to make out his
opinions.
174 See Schaubach, ad Anax. Fr. p. 174-181.
Among the points to which Anaxagoras addressed
himself was the annual inundation of the Nile, which he
ascribed to the melting of the snows in Æthiopia, in the
higher regions of the river’s course. — Diodor. i. 38.
Herodotus notices this opinion (ii. 22), calling it plausible,
but false, yet without naming any one as its author.
Compare Euripides, Helen. 3.
175 Aristotel. De Generat. Animal. iii. 6, iv. 1.
176 Theophrastus, Hist. Plant. iii. 2; Diogen. Laert. ii. 9;
Aristot. De Plantis, i. 2.
177 Aristot. De Plantis, i. 1; Aristot. Part. Animal. iv. 10.
178 Theophrastus, De Sensu, sect. 1 — sect. 27-30.
This difference followed naturally from the opinions of
the two philosophers on the nature of the soul or mind.
Anaxagoras supposed it peculiar in itself, and dissimilar to
the Homœomeries without. Empedokles conceived it as a
compound of the four elements, analogous to all that
was without: hence man knew each exterior element by

its like within himself — earth by earth, water by water,
c.
179 Anaxag. Fr. 19, Schaub.; Sextus Empiric. adv.
Mathem. vii. 91-140; Cicero, Academ. i. 12.
Anaxagoras remarked that the contrast between black
and white might be made imperceptible to sense by a
succession of numerous intermediate colours very finely
graduated. He is said to have affirmed that snow was
really black, notwithstanding that it appeared white to
our senses: since water was black, and snow was only
frozen water (Cicero, Academ. iv. 31; Sext. Empir.
Pyrrhon. Hypotyp. i. 33). “Anaxagoras non modo id ita
esse (sc. albam nivem esse) negabat, sed sibi, quia sciret
aquam nigram esse, unde illa concreta esset, albam
ipsam esse ne videri quidem.” Whether Anaxagoras ever
affirmed that snow did not appear to him white, may
reasonably be doubted: his real affirmation probably was,
that snow, though it appeared white, was not really
white. And this affirmation depended upon the line which
he drew between the fact of sense, the phenomenal, the
relative, on one side — and the substratum, the real, the
absolute, on the other. Most philosophers recognise a
distinction between the two; but the line between the
two has been drawn in very different directions.
Anaxagoras assumed as his substratum, real, or absolute,
the Homœomeries — numerous primordial varieties of
matter, each with its inherent qualities. Among these
varieties he reckoned water, but he did not reckon snow.
He also considered that water was really and absolutely
black or dark (the Homeric μέλαν ὕδωρ) — that
blackness was among its primary qualities. Water, when

The doctrines of
Anaxagoras were regarded
as offensive and impious.
consolidated into snow, was so disguised as to produce
upon the spectator the appearance of whiteness; but it
did not really lose, nor could it lose, its inherent colour. A
negro covered with white paint, and therefore looking
white, is still really black: a wheel painted with the seven
prismatic colours, and made to revolve rapidly, will look
white, but it is still really septi-coloured: i.e. the state of
rapid revolution would be considered as an exceptional
state, not natural to it. Compare Plato, Lysis, c. 32, p.
217 D.
Anaxagoras, residing at Athens and
intimately connected with Perikles,
incurred not only unpopularity, but even
legal prosecution, by the tenor of his
philosophical opinions, especially those on astronomy. To Greeks who
believed in Helios and Selênê as not merely living beings but Deities, his
declaration that the Sun was a luminous and fiery stone, and the Moon
an earthy mass, appeared alike absurd and impious. Such was the
judgment of Sokrates, Plato, and Xenophon, as well as of Aristophanes
and the general Athenian public.180 Anaxagoras was threatened with
indictment for blasphemy, so that Perikles was compelled to send him
away from Athens.

Diogenes of Apollonia
recognises one primordial
element.
180 Plato, Apol. So. c. 14; Xenoph. Memor. iv. 7.
That physical enquiries into the nature of things, and attempts to
substitute scientific theories in place of the personal agency of the
Gods, were repugnant to the religious feelings of the Greeks, has
been already remarked.181 Yet most of the other contemporary
philosophers must have been open to this reproach, not less than
Anaxagoras; and we learn that the Apolloniate Diogenes left Athens
from the same cause. If others escaped the like prosecution which
fell upon Anaxagoras, we may probably ascribe this fact to the state
of political party at Athens, and to the intimacy of the latter with
Perikles. The numerous political enemies of that great man might
fairly hope to discredit him in the public mind — at the very least to
vex and embarrass him — by procuring the trial and condemnation
of Anaxagoras. Against other philosophers, even when propounding
doctrines not less obnoxious respecting the celestial bodies, there
was not the same collateral motive to stimulate the aggressive
hostility of individuals.
181 Plutarch, Nikias, 23.
Contemporary with Anaxagoras —
yet somewhat younger, as far as we
can judge, upon doubtful evidence —
lived the philosopher Diogenes, a
native of Apollonia in Krete. Of his life we know nothing except that
he taught during some time at Athens, which city he was forced to
quit on the same ground as Anaxagoras. Accusations of impiety were
either brought or threatened against him:182 physical philosophy
being offensive generally to the received religious sentiment, which

was specially awakened and appealed to by the political opponents
of Perikles.
182 Diogen. Laert. ix. 52. The danger incurred by
Diogenes the Apolloniate at Athens is well
authenticated, on the evidence of Demetrius the
Phalerean, who had good means of knowing. And the
fact may probably be referred to some time after the
year B.C. 440, when Athens was at the height of her
power and of her attraction for foreign visitors — when
the visits of philosophers to the city had been
multiplied by the countenance of Perikles — and when
the political rivals of that great man had set the
fashion of assailing them in order to injure him. This
seems to me one probable reason for determining the
chronology of the Apolloniate Diogenes: another is,
that his description of the veins in the human body is
so minute and detailed as to betoken an advanced
period of philosophy between B.C. 440-410. See the
point discussed in Panzerbieter, Fragment. Diogen.
Apoll. c. 12-18 (Leipsic, 1830).
Simplikius (ad Aristot. Phys. fol. 6 A) describes
Diogenes as having been σχεδὸν νεώτατος in the
series of physical theorists.
Diogenes the Apolloniate, the latest in the series of Ionic
philosophers or physiologists, adopted, with modifications and
enlargements, the fundamental tenet of Anaximenes. There was but
one primordial element — and that element was air. He laid it down
as indisputable that all the different objects in this Kosmos must be
at the bottom one and the same thing: unless this were the fact,

Air was the primordial,
universal element.
they would not act upon each other, nor mix together, nor do good
and harm to each other, as we see that they do. Plants would not
grow out of the earth, nor would animals live and grow by nutrition,
unless there existed as a basis this universal sameness of nature. No
one thing therefore has a peculiar nature of its own: there is in all
the same nature, but very changeable and diversified.183
183 Diogen. Ap. Fragm. ii. c. 29 Panzerb.;
Theophrastus, De Sensu, s. 39.
εἰ γὰρ τὰ ἐν τῷδε τῷ κόσμῳ ἐόντα νῦν γῆ καὶ ὕδωρ
καὶ τἄλλα, ὅσα φαινεται ἐν τῷδε τῷ κόσμῳ ἐόντα, εἰ
τουτέων τι ἦν τὸ ἕτερον τοῦ ἑτέρου ἕτερον ἐὸν τῇ ἰδίῃ
φύσει, καὶ μὴ τὸ αὐτὸ ἐὸν μετέπιπτε πολλαχῶς καὶ
ἡτεροιοῦτο· οὐδαμῆ οὔτε μίσγεσθαι ἀλλήλοις ἠδύνατο
οὔτε ὠφέλησις τῷ ἑτέρῳ οὔτε βλάβη, c.
Aristotle approves this fundamental tenet of
Diogenes, the conclusion that there must be one
common Something out of which all things came — ἐξ
ἑνὸς ἅπαντα (Gen. et Corrupt. i. 6-7, p. 322, a. 14),
inferred from the fact that they acted upon each other.
Now the fundamental substance,
common to all, was air. Air was infinite,
eternal, powerful; it was, besides, full
of intelligence and knowledge. This latter property Diogenes proved
by the succession of climatic and atmospheric phenomena of winter
and summer, night and day, rain, wind, and fine weather. All these
successions were disposed in the best possible manner by the air:
which could not have laid out things in such regular order and
measure, unless it had been endowed with intelligence. Moreover,

Air possessed numerous
and diverse properties; was
eminently modifiable.
air was the source of life, soul, and intelligence, to men and animals:
who inhaled all these by respiration, and lost all of them as soon as
they ceased to respire.184
184 Diog. Apoll. Fr. iv.-vi. c. 36-42, Panz. — Οὐ γὰρ ἂν
οὕτω δέδασθαι οἷόν τε ἦν ἄνευ νοήσιος, ὥστε πάντων
μέτρα ἔχειν, χειμῶνός τε καὶ θέρεος και νυκτὸς καὶ
ἡμέρης καὶ ὑετῶν καὶ ἀνέμων καὶ εὐδιῶν. καὶ τὰ ἄλλα
εἴ τις βούλεται ἐννοέεσθαι, εὕρισκοι ἂν οὕτω
διακείμενα, ὡς ἀνυστὸν κάλλιστα. Ἔτι δε πρὸς τούτοις
καὶ τάδε μεγάλα σημεῖα· ἄνθρωπος γὰρ καὶ τὰ ἄλλα
ζῶα ἀναπνέοντα ζώει τῷ ἀέρι. Καὶ τοῦτο αὐτοῖς καὶ
ψυχή ἐστι καὶ νόησις ——
— Καὶ μοὶ δοκέει τὸ τὴν νόησιν ἔχον εἶναι ὁ ἀὴρ
καλεόμενος ὑπὸ τῶν ἀνθρώπων, c.
Schleiermacher has an instructive commentary upon
these fragments of the Apolloniate Diogenes
(Vermischte Schriften, vol. ii. p. 157-162; Ueber
Diogenes von Apollonia).
Air, life-giving and intelligent, existed
everywhere, formed the essence of
everything, comprehended and
governed everything. Nothing in nature
could be without it: yet at the same time all things in nature partook
of it in a different manner.185 For it was distinguished by great
diversity of properties and by many gradations of intelligence. It was
hotter or colder — moister or drier — denser or rarer — more or less
active and movable — exhibiting differences of colour and taste. All
these diversities were found in objects, though all at the bottom

Physiology of Diogenes —
his description of the veins
in the human body.
were air. Reason and intelligence resided in the warm air. So also to
all animals as well as to men, the common source of vitality,
whereby they lived, saw, heard, and understood, was air; hotter
than the atmosphere generally, though much colder than that near
the sun.186 Nevertheless, in spite of this common characteristic, the
air was in other respects so indefinitely modifiable, that animals
were of all degrees of diversity, in form, habits, and intelligence. Men
were doubtless more alike among themselves: yet no two of them
could be found exactly alike, furnished with the same dose of aerial
heat or vitality. All other things, animate and inanimate, were
generated and perished, beginning from air and ending in air: which
alone continued immortal and indestructible.187
185 Diog. Ap. Fr. vi. καὶ ἐστι μηδὲ ἓν ὅ, τι μὴ μετέχει
τούτου (air). Μετέχει δὲ οὐδὲ ἓν ὁμοίως τὸ ἕτερον τῷ
ἑτέρῳ· ἀλλὰ πολλοὶ τρόποὶ καὶ αὐτοὺ τοῦ ἀέρος καὶ
τῆς νοήσιός εἰσιν.
Aristotel. De Animâ, i. 2, p. 405, a. 21. Διογένης δ’,
ὥσπερ καὶ ἑτεροί τινες, ἀέρα [ὑπέλαβε τὴν ψυχήν], c.
186 Diog. Ap. Fr. vi. καὶ πάντων ζώων δὴ ἡ ψυχὴ τὸ
αὐτό ἐστιν, ἀὴρ θερμότερος μὲν τοῦ ἔξω ἐν ᾧ ἐσμέν,
τοῦ μέντοι παρὰ τῷ ἡελίῳ πολλὸν ψυχρότερος.
187 Diogen. Apoll. Fr. v. ch. 38, Panz.
The intelligence of men and animals,
very unequal in character and degree,
was imbibed by respiration, the
inspired air passing by means of the
veins and along the blood into all parts of the body. Of the veins
Diogenes gave a description remarkable for its minuteness of detail,

in an age when philosophers dwelt almost exclusively in loose
general analogies.188 He conceived the principal seat of intelligence
in man to be in the thoracic cavity, or in the ventricle of the heart,
where a quantity of air was accumulated ready for distribution.189
The warm and dry air concentrated round the brain, and reached by
veins from the organs of sense, was the centre of sensation. Taste
was explained by the soft and porous nature of the tongue, and by
the number of veins communicating with it. The juices of sapid
bodies were sucked up by it as by a sponge: the odorous stream of
air penetrated from without through the nostrils: both were thus
brought into conjunction with the sympathising cerebral air. To this
air also the image impressed upon the eye was transmitted, thereby
causing vision:190 while pulsations and vibrations of the air without,
entering through the ears and impinging upon the same centre,
generated the sensation of sound. If the veins connecting the eye
with the brain were inflamed, no visual sensation could take
place;191 moreover if our minds or attention were absorbed in other
things, we were often altogether insensible to sensations either of
sight or of sound: which proved that the central air within us was
the real seat of sensation.192 Thought and intelligence, as well as
sensation, was an attribute of the same central air within us,
depending especially upon its purity, dryness, and heat, and
impeded or deadened by moisture or cold. Both children and animals
had less intelligence than men: because they had more moisture in
their bodies, so that the veins were choked up, and the air could not
get along them freely to all parts. Plants had no intelligence; having
no apertures or ducts whereby the air could pervade their internal
structure. Our sensations were pleasurable when there was much air
mingled with the blood, so as to lighten the flow of it, and to carry it

easily to all parts: they were painful when there was little air, and
when the blood was torpid and thick.193
188 Diogen. Apoll. Fr. vii. ch. 48, Panz. The
description of the veins given by Diogenes is preserved
in Aristotel. Hist. Animal, iii. 2: yet seemingly only in a
defective abstract, for Theophrastus alludes to various
opinions of Diogenes on the veins, which are not
contained in Aristotle. See Philippson, Ὕλη ἀνθρωπίνη,
p. 203.
189 Plutarch, Placit. Philos. iv. 5. Ἐν τῇ ἀρτηριακῇ
κοιλίᾳ τῆς καρδίας, ἥτις ἐστὶ καὶ πνευματική. See
Panzerbieter’s commentary upon these words, which
are not very clear (c. 50), nor easy to reconcile with
the description given by Diogenes himself of the veins.
190 Plutarch, Placit. Philosoph. iv. 18. Theophrast. De
Sensu, s. 39-41-43. Κριτικώτατον δὲ ἡδονῆς τὴν
γλῶτταν· ἁπαλώτατον γὰρ εἶναι καὶ μανὸν καὶ τὰς
φλέβας ἁπάσας ἀνήκειν εἰς αὐτήν.
191 Plutarch, Placit. Philosoph. iv. 16; Theophrastus,
De Sensu, s. 40.
192 Theophrast. De Sensu, s. 42. Ὅτι δὲ ὁ ἐντὸς ἀὴρ
αἰσθάνεται, μικρὸν ὢν μόριον τοῦ θεοῦ, σημεῖον εἶναι,
ὅτι πολλάκις πρὸς ἄλλα τὸν νοῦν ἔχοντες οὔθ’ ὁρῶμεν
οὔτ’ ἀκούομεν. The same opinion — that sensation,
like thought, is a mental process, depending on
physical conditions — is ascribed to Strato (the disciple
and successor of Theophrastus) by Porphyry, De
Abstinentiâ, iii. 21. Στράτωνος τοῦ φυσικοῦ λόγος

Kosmology and
meteorology.
ἐστὶν ἀποδεικνύων, ὡς οὐδὲ αἰσθάνεσθαι το παράπαν
ἄνευ τοῦ νοεῖν ὑπάρχει. καὶ γὰρ γράμματα πολλάκις
ἐπιπορευομένους τῇ ὄψει καὶ λόγοι προσπίπτοντες τῇ
ἀκοῇ διαλανθάνουσιν ἡμᾶς καὶ διαφεύγουσι πρὸς
ἑτέρους τὸν νοῦν ἔχοντας — ᾗ καὶ λέλεκται, νοῦς ὁρῆ
καὶ νοῦς ἀκούει, τἄλλα κωφὰ καὶ τυφλά.
The expression ascribed to Diogenes by
Theophrastus — ὁ ἐντὸς ἀὴρ, μικρὸν ὢν μόριον τ ο ῦ
θ ε ο ῦ — is so printed by Philippson; but the word
θεοῦ seems not well avouched as to the text, and
Schneider prints θυμοῦ. It is not impossible that
Diogenes may have called the air God, without
departing from his physical theory; but this requires
proof.
193 Theophrastus, De Sensu, s. 43-46; Plutarch,
Placit. Philos. v. 20. That moisture is the cause of
dulness, and that the dry soul is the best and most
intelligent — is cited among the doctrines of
Herakleitus, with whom Diogenes of Apollonia is often
in harmony. Αὔη ψυχὴ σοφωτάτη καὶ ἀρίστη. See
Schleiermach. Herakleitos, sect. 59-64.
The structure of the Kosmos
Diogenes supposed to have been
effected by portions of the infinite air,
taking upon them new qualities and undergoing various
transformations. Some air, becoming cold, dense, and heavy, sunk
down to the centre, and there remained stationary as earth and
water: while the hotter, rarer, and lighter air ascended and formed
the heavens, assuming through the intelligence included in it a rapid

rotatory movement round the earth, and shaping itself into sun,
moon, and stars, which were light and porous bodies like pumice
stone. The heat of this celestial matter acted continually upon the
earth and water beneath, so that the earth became comparatively
drier, and the water was more and more drawn up as vapour, to
serve for nourishment to the heavenly bodies. The stars also acted
as breathing-holes to the Kosmos, supplying the heated celestial
mass with fresh air from the infinite mass without.194 Like
Anaxagoras, Diogenes conceived the figure of the earth as flat and
round, like a drum; and the rotation of the heavens as lateral, with
the axis perpendicular to the surface of the earth, and the north pole
always at the zenith. This he supposed to have been the original
arrangement; but after a certain time, the earth tilted over
spontaneously towards the south — the northern half was elevated
and the southern half depressed — so that the north pole was no
longer at the zenith, and the axis of rotation of the heavens became
apparently oblique.195 He thought, moreover, that the existing
Kosmos was only of temporary duration; that it would perish and be
succeeded by future analogous systems, generated from the same
common substance of the infinite and indestructible air.196
Respecting animal generation — and to some extent respecting
meteorological phenomena197 — Diogenes also propounded several
opinions, which are imperfectly known, but which appear to have
resembled those of Anaxagoras.
194 Plutarch ap. Eusebium Præp. Evang. i. 8;
Aristotel. De Animâ, i. 2; Diogen. Laert. ix. 53.
Διογένης κισσηροειδῆ τὰ ἄστρα, διαπνοίας δὲ αὐτὰ
νομίζει τοῦ κόσμου, εἶναι δὲ διάπυρα· συμπεριφέρεσθαι
δὲ τοῖς φανεροῖς ἄστροις ἀφανεῖς λίθους καὶ παρ’ αὐτὸ
τοῦτ’ ἀνωνύμους· πίπτοντα δὲ πολλάκις ἐπὶ τῆς γῆς

Leukippus and Demokritus
— Atomic theory.
σβέννυσθαι· καθάπερ τὸν ἐν Αἰγὸς ποταμοῖς πυρωδῶς
κατενεχθέντα ἀ σ τ έ ρ α πέτρινον. This remarkable
anticipation of modern astronomy — the recognition of
aerolithes as a class of non-luminous earthy bodies
revolving round the sun, but occasionally coming
within the sphere of the earth’s attraction, becoming
luminous in our atmosphere, falling on the earth, and
there being extinguished — is noticed by Alex. von
Humboldt in his Kosmos, vol. i. p. 98-104, Eng. trans.
He says — “The opinion of Diogenes of Apollonia
entirely accords with that of the present day,” p. 110.
The charm and value of that interesting book is greatly
enhanced by his frequent reference to the ancient
points of view on astronomical subjects.
195 Plutarch, Placit. Philos. ii. 8; Panzerbieter ad Diog.
Ap. c. 76-78; Schaubach ad Anaxagor. Fr. p. 175.
196 Plut. Ap. Euseb. Præp. Evang. i. 8.
197 Preller, Hist. Philosoph. Græc.-Rom. ex Font. Loc.
Contexta, sect. 68. Preller thinks that Diogenes
employed his chief attention “in animantium naturâ ex
aeris principio repetendâ”; and that he was less full “in
cognitione τῶν μετεώρων”. But the fragments scarcely
justify this.
Nearly contemporary with
Anaxagoras and Empedokles, two other
enquirers propounded a new physical
theory very different from those already noticed — usually known
under the name of the atomic theory. This Atomic theory, though

Long life, varied travels,
and numerous
compositions of
Demokritus.
originating with the Eleate Leukippus, obtained celebrity chiefly from
his pupil Demokritus of Abdera, its expositor and improver.
Demokritus (born seemingly in B.C. 460, and reported to have
reached extreme old age) was nine years younger than Sokrates,
thirty-three years older than Plato, and forty years younger than
Anaxagoras.198 The age of Leukippus is not known, but he can
hardly have been much younger than Anaxagoras.
198 Diogen. Laert. ix. 41. See the chronology of
Demokritus discussed in Mullach, Frag. Dem. p. 12-25;
and in Zeller, Phil. der Griech., vol. i. p. 576-681, 2nd
edit. The statement of Apollodorus as to the date of
his birth, appears more trustworthy than the earlier
date assigned by Thrasyllus (B.C. 470). Demokritus
declared himself to be forty years younger than
Anaxagoras.
Of Leukippus we know nothing: of
Demokritus, very little — yet enough to
exhibit a life, like that of Anaxagoras,
consecrated to philosophical
investigation, and neglectful not merely
of politics, but even of inherited patrimony.199 His attention was
chiefly turned towards the study of Nature, with conceptions less
vague, and a more enlarged observation of facts, than any of his
contemporaries had ever bestowed. He was enabled to boast that no
one had surpassed him in extent of travelling over foreign lands, in
intelligent research and converse with enlightened natives, or in
following out the geometrical relations of lines.200 He spent several
years in visiting Egypt, Asia Minor, and Persia. His writings were
numerous, and on many different subjects, including ethics, as well

as physics, astronomy, and anthropology. None of them have been
preserved. But we read, even from critics like Dionysius of
Halikarnassus and Cicero, that they were composed in an impressive
and semi-poetical style, not unworthy to be mentioned in analogy
with Plato; while in range and diversity of subjects they are hardly
inferior to Aristotle.201
199 Dionys. ix. 36-39.
200 Demokrit. Fragm. 6, p. 238, ed. Mullach.
Compare ib. p. 41; Diogen. Laert. ix. 35; Strabo, xv. p.
703.
Pliny, Hist. Natur. “Democritus — vitam inter
experimenta consumpsit,” c.
201 Cicero, Orat. c. 20; Dionys. De Comp. Verbor. c.
24; Sextus Empir. adv. Mathem. vii. 265. Δημόκριτος, ὁ
τῇ Διὸς φώνῃ παρεικαζόμενος, c.
Diogenes (ix. 46-48) enumerates the titles of the
treatises of Demokritus, as edited in the days of
Tiberius by the rhetor Thrasyllus: who distributed them
into tetralogies, as he also distributed the dialogues of
Plato. It was probably the charm of style, common to
Demokritus with Plato, which induced the rhetor thus
to edit them both. In regard to scope and spirit of
philosophy, the difference between the two was so
marked, that Plato is said to have had a positive
antipathy to the works of Demokritus, and a desire to
burn them (Aristoxenus ap. Diog. Laert. ix. 40). It
could hardly be from congeniality of doctrine that the
same editor attached himself to both. It has been

Relation between the
theory of Demokritus and
that of Parmenides.
remarked that Plato never once names Demokritus,
while Aristotle cites him very frequently, sometimes
with marked praise.
The theory of Leukippus and
Demokritus (we have no means of
distinguishing the two) appears to have
grown out the Eleatic theory.202
Parmenides the Eleate (as I have already stated) in distinguishing
Ens, the self-existent, real, or absolute, on one side — from the
phenomenal and relative on the other — conceived the former in
such a way that its connection with the latter was dissolved. The real
and absolute, according to him, was One, extended, enduring,
continuous, unchangeable, immovable: the conception of Ens
included these affirmations, and at the same time excluded
peremptorily Non-Ens, or the contrary of Ens. Now the plural,
unextended, transient, discontinuous, changeable, and moving,
implied a mixture of Ens and Non-Ens, or a partial transition from
one to the other. Hence (since Non-Ens was inadmissible) such
plurality, c., could not belong to the real or absolute (ultra-
phenomenal), and could only be affirmed as phenomenal or relative.
In the latter sense, Parmenides did affirm it, and even tried to
explain it: he explained the phenomenal facts from phenomenal
assumptions, apart from and independent of the absolute. While
thus breaking down the bridge between the phenomenal on one side
and the absolute on the other, he nevertheless recognised each in a
sphere of its own.
202 Simplikius, in Aristotel. Physic. fol. 7 A. Λεύκιππος
… κοινωνήσας Παρμενίδῃ τῆς φιλοσοφίας, οὐ τὴν
αὐτὴν ἐβάδισε Παρμενίδῃ καὶ Ξενοφάνει περὶ τῶν

Demokritean theory —
Atoms — Plena and Vacua
— Ens and Non-Ens.
ὄντων δόξαν, ἀλλ’, ὡς δοκεῖ, τὴν ἐναντίαν. Aristotel.
De Gener. et Corr. i. 8, p. 251, a. 31. Diogen. Laert. ix.
30.
This bridge the atomists undertook
to re-establish. They admitted that Ens
could not really change — that there
could be no real generation, or
destruction — no transformation of qualities — no transition of many
into one, or of one into many. But they denied the unity and
continuity and immobility of Ens: they affirmed that it was essentially
discontinuous, plural, and moving. They distinguished the extended,
which Parmenides had treated as an Unum continuum, into
extension with body, and extension without body: into plenum and
vacuum, matter and space. They conceived themselves to have thus
found positive meanings both for Ens and Non-Ens. That which
Parmenides called Non-Ens or nothing, was in their judgment the
vacuum; not less self-existent than that which he called Something.
They established their point by showing that Ens, thus interpreted,
would become reconcilable to the phenomena of sense: which latter
they assumed as their basis to start from. Assuming motion as a
phenomenal fact, obvious and incontestable, they asserted that it
could not even appear to be a fact, without supposing vacuum as
well as body to be real: and the proof that both of them were real
was, that only in this manner could sense and reason be reconciled.
Farther, they proved the existence of a vacuum by appeal to direct
physical observation, which showed that bodies were porous,
compressible, and capable of receiving into themselves new matter
in the way of nutrition. Instead of the Parmenidean Ens, one and
continuous, we have a Demokritean Ens, essentially many and
discontinuous: plena and vacua, spaces full and spaces empty, being

infinitely intermingled.203 There existed atoms innumerable, each
one in itself essentially a plenum, admitting no vacant space within
it, and therefore indivisible as well as indestructible: but each
severed from the rest by surrounding vacant space. The atom could
undergo no change: but by means of the empty space around, it
could freely move. Each atom was too small to be visible: yet all
atoms were not equally small; there were fundamental differences
between them in figure and magnitude: and they had no other
qualities except figure and magnitude. As no atom could be divided
into two, so no two atoms could merge into one. Yet though two or
more atoms could not so merge together as to lose their real
separate individuality, they might nevertheless come into such close
approximation as to appear one, and to act on our senses as a
phenomenal combination manifesting itself by new sensible
properties.204
203 It is chiefly in the eighth chapter of the treatise
De Gener. et Corr. (i. 8) that Aristotle traces the
doctrine of Leukippus as having grown out of that of
the Eleates. Λεύκιππος δ’ ἔχειν ᾠήθη λόγους, οἵτινες
πρὸς τὴν αἴσθησιν ὁμολογούμενα λέγοντες οὐκ
ἀναιρήσουσιν οὔτε γένεσιν οὔτε φθορὰν οὔτε κίνησιν
καὶ τὸ πλῆθος τῶν ὄντων, c.
Compare also Aristotel. De Cœlo, iii. 4, p. 303, a. 6;
Metaphys. A. 4, p. 985, b. 5; Physic. iv. 6: λέγουσι δὲ
(Demokritus, c., in proving a vacuum) ἓν μὲν ὅτι ἡ
κίνησις ἡ κατὰ τόπον οὐκ ἂν εἴη, ο ὐ γ ὰ ρ ἂ ν
δ ο κ ε ῖ ν εἶναι κίνησιν εἰ μὴ εἴη κενόν· τὸ γὰρ πλῆρες
ἀδύνατον εἶναι δέξασθαί τι, c.

Plutarch adv. Kolot. p. 1108. Οἷς οὐδ’ ὄναρ ἐντυχὼν
ὁ Κολώτης, ἐσφάλη περὶ λέξιν τοῦ ἀνδρὸς
(Demokritus) ἐν ᾖ διορίζεται, μὴ μᾶλλον τὸ δὲν, ἢ τὸ
μηδὲν εἶναι· δὲν μὲν ὀνομάζων τὸ σῶμα μηδὲν δὲ τὸ
κενόν, ὡς καὶ τούτου φύσιν τινὰ καὶ ὑπόστασιν ἰδίαν
ἔχοντος.
The affirmation of Demokritus — That Nothing
existed, just as much as Something — appears a
paradox which we must probably understand as
implying that he here adopted, for the sake of
argument, the language of the Eleates, his opponents.
They called the vacuum Nothing, but Demokritus did
not so call it. If (said Demokritus) you call vacuum
Nothing, then I say that Nothing exists as well as
Something.
The direct observations by which Demokritus
showed the existence of a vacuum were — 1. A vessel
with ashes in it will hold as much water as if it were
empty: hence we know that there are pores in the
ashes, into which the water is received. 2. Wine can be
compressed in skins. 3. The growth of organised
bodies proves that they have pores, through which
new matter in the form of nourishment is admitted.
(Aristot. Physic. iv. 6, p. 213, b.)
Besides this, Demokritus set forth motion as an
indisputable fact, ascertained by the evidence of
sense: and affirmed that motion was impossible,
except on the assumption that vacuum existed.
Melissus, the disciple of Parmenides, inverted the

Primordial atoms differed
only in magnitude, figure,
position, and arrangement
— they had no qualities,
but their movements and
combinations generated
qualities.
reasoning, in arguing against the reality of motion. If it
be real (he said), then there must exist a vacuum: but
no vacuum does or can exist: therefore there is no real
motion. (Aristot. Physic. iv. 6.)
Since Demokritus started from these facts of sense,
as the base of his hypothesis of atoms and vacua, so
Aristotle (Gen. et Corr. i. 2; De Animâ, i. 2) might
reasonably say that he took sensible appearances as
truth. But we find Demokritus also describing reason
as an improvement and enlightenment of sense, and
complaining how little of truth was discoverable by
man. See Mullach, Demokritus (pp. 414, 415).
Compare Philippson — Ὗλη ἀνθρωπίνη — Berlin, 1831.
204 Aristotel. Gen. et Corr. i. 8, p. 325, a. 25, τὰ
πρῶτα μεγέθη τὰ ἀδιαίρετα στερεά. Diogen. Laert. ix.
44; Plutarch, adv. Koloten, p. 1110 seq.
Zeller, Philos. der Griech., vol. i. p. 583-588, ed. 2nd;
Aristotel. Metaphys. Z. 13, p. 1039, a. 10, ἀδύνατον
εἶναί φησι Δημόκριτος ἐκ δύο ἓν ᾒ ἐξ ἑνὸς δύο
γενέσθαι· τὰ γὰρ μεγέθη τὰ ἄτομα τὰς οὐσίας ποιεῖ.
The bridge, broken down by
Parmenides, between the real and the
phenomenal world, was thus in theory
re-established. For the real world, as
described by Demokritus, differed
entirely from the sameness and
barrenness of the Parmenidean Ens,
and presented sufficient movement and

variety to supply a basis of explanatory hypothesis, accommodated
to more or less of the varieties in the phenomenal world. In respect
of quality, indeed, all the atoms were alike, not less than all the
vacua: such likeness was (according to Demokritus) the condition of
their being able to act upon each other, or to combine as
phenomenal aggregates.205 But in respect to quantity or magnitude
as well as in respect to figure, they differed very greatly: moreover,
besides all these diversities, the ordination and position of each
atom with regard to the rest were variable in every way. As all
objects of sense were atomic compounds, so, from such
fundamental differences — partly in the constituent atoms
themselves, partly in the manner of their arrangement when thrown
into combination — arose all the diverse qualities and manifestations
of the compounds. When atoms passed into new combination, then
there was generation of a new substance: when they passed out of
an old combination there was destruction: when the atoms remained
the same, but were merely arranged anew in order and relative
position, then the phenomenon was simply change. Hence all
qualities and manifestations of such compounds were not original,
but derivative: they had no “nature of their own,” or law peculiar to
them, but followed from the atomic composition of the body to
which they belonged. They were not real and absolute, like the
magnitude and figure of the constituent atoms, but phenomenal and
relative — i.e. they were powers of acting upon correlative organs of
sentient beings, and nullities in the absence of such organs.206 Such
were the colour, sonorousness, taste, smell, heat, cold, c., of the
bodies around us: they were relative, implying correlative
percipients. Moreover they were not merely relative, but perpetually
fluctuating; since the compounds were frequently changing either in
arrangement or in diversity of atoms, and every such atomic change,

even to a small extent, caused it to work differently upon our
organs.207
205 Aristotel. Gener. et Corr. i. 7, p. 323, b. 12. It was
the opinion of Demokritus, that there could be no
action except where agent and patient were alike.
Φησὶ γὰρ τὸ αὐτὸ καὶ ὅμοιον εἶναι τό τε ποιοῦν καὶ τὸ
πάσχον· οὐ γὰρ ἐγχωρεῖν τὰ ἕτερα καὶ διαφέροντα
πάσχειν ὑπ’ ἀλλήλων· ἀλλὰ κἂν ἕτερα ὄντα ποιῇ τι εἰς
ἄλληλα, οὐχ ᾗ ἕτερα, ἀλλ’ ᾗ ταὐτόν τι ὑπάρχει, ταύτῃ
τοῦτο συμβαίνειν αὐτοῖς. Many contemporary
philosophers affirmed distinctly the opposite. Τὸ
ὅμοιον ὑπὸ τοῦ ὁμοίου πᾶν ἀπαθές, c. Diogenes the
Apolloniate agreed on this point generally with
Demokritus; see above, p. 61, note 1. The facility with
which these philosophers laid down general maxims is
constantly observable.
206 Aristot. Gen. et Corr. i. 2, p. 316, a. 1;
Theophrast. De Sensu, s. 63, 64. Περὶ μὲν οὖν βαρέος
καὶ κούφου καὶ σκληροῦ καὶ μαλακοῦ ἐν τούτοις
ἀφορίζει· τῶν δὲ ἄλλων αἰσθητῶν οὐδενὸς εἶναι φύσιν,
ἀλλὰ πάντα πάθη τῆς αἰσθήσεως ἀλλοιουμένης, ἐξ ἧς
γίνεσθαι τὴν φαντασίαν, c.
Stobæus, Eclog. Physic. i. c. 16. Φύσιν μὲν μηδὲν
εἶναι χρῶμα, τὰ μὲν γὰρ στοιχεῖα ἄποια, τά τε μεστὰ
καὶ τὸ κενόν· τὰ δ’ ἐξ αὐτῶν συγκρίματα κέχρῶσθαι
διαταγῇ τε καὶ ῥυθμῷ καὶ προτροπῇ, c.
Demokritus restricted the term Φύσις — Nature — to
the primordial atoms and vacua (Simplikius ad Aristot.

Combinations of atoms —
generating different
qualities in the compounds.
Physic. p. 310 A.).
207 Aristotel. Gener. et Corr. i. 2, p. 315, b. 10. Ὥστε
ταῖς μεταβολαῖς τοῦ συγκειμένου τὸ αὐτὸ ἐναντίον
δοκεῖν ἄλλῳ καὶ ἄλλῳ, καὶ μετακινεῖσθαι μικροῦ
ἐμμιγνυμένου, κ α ὶ ὅ λ ω ς ἕ τ ε ρ ο ν φ α ί ν ε σ θ α ι
ἑ ν ὸ ς μ ε τ α κ ι ν η θ έ ν τ ο ς .
Among the various properties of
bodies, however, there were two which
Demokritus recognised as not merely
relative to the observer, but also as
absolute and belonging to the body in itself. These were weight and
hardness — primary qualities (to use the phraseology of Locke and
Reid), as contrasted with the secondary qualities of colour, taste, and
the like. Weight, or tendency downward, belonged (according to
Demokritus) to each individual atom separately, in proportion to its
magnitude: the specific gravity of all atoms was supposed to be
equal. In compound bodies one body was heavier than another, in
proportion as its bulk was more filled with atoms and less with
vacant space.208 The hardness and softness of bodies Demokritus
explained by the peculiar size and peculiar junction of their
component atoms. Thus, comparing lead with iron, the former is
heavier and softer, the latter is lighter and harder. Bulk for bulk, the
lead contained a larger proportion of solid, and a smaller proportion
of interstices, than the iron: hence it was heavier. But its structure
was equable throughout; it had a greater multitude of minute atoms
diffused through its bulk, equally close to and coherent with each
other on every side, but not more close and coherent on one side
than on another. The structure of the iron, on the contrary, was
unequal and irregular, including larger spaces of vacuum in one part,

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