Java Software Solutions
Chapter 1
Computer Systems
1
Basic Computer Processing
 A computer system is made up of hardware
and software.


Hardware: Chips, keyboards, disks, etc.
Software: Programs and the data those
programs use.
 Key Components of a Computer System
 central processing unit (CPU)
 input/output (I/O) devices
 main memory
 secondary memory devices
2
Memory
 Programs and data are held in storage devices called
memory, which fall into two categories:


Main Memory
 The storage device (e.g., chips on the mother board)
that holds the programs and their data (software) while
the programs are executing.
Secondary Memory
 Devices such as hard disks that store software in a
relatively permanent manner.
 We save our software on secondary memory.
Copies of the software are brought into main
memory when we execute our programs.
3
Software Categories
 We will be concerned with two categories of software.
 The operating system.
 Provides a user interface that allows us to interact with
the machine (enter input and view output).
 Manages computer resources such as the CPU and
main memory.
 Application Software
 Generic term for just about any software other than
the operating system.
 Word processors, web browsers, games, business
applications, etc.
 The focus of this course is development of highquality application programs.
4
What This Means to Us
 We will be learning to create application programs
using the Java programming language.


Initially, the hardware we will use is a computer named
Osprey that is located on campus, but can be
accessed from home.
Our software will be the Linux operating system,
one of two text editors (vi or Pico), the Java
compiler (javac), and the Java interpreter (java).
 Other software such as communications software, etc.
will be used, but will not require much interaction on
our part.
5
Analog versus Digital Signals
 Two fundamental techniques are used to store and
manage information in a computer system.

Analog information is continuous, varying in direct
proportion to the source of the information. An oldfashioned record used analog technology to store
music.
 Digital technology breaks information into discrete
pieces and represents the pieces as numbers.

Music on a CD is stored digitally, as a series of
numbers. The music is sampled about 40,000 times
per second and each number represents the voltage
level of one specific instance of the recording.
6
An Analog Signal
versus a Digital Signal
analog
digital
7
Binary Numbers
 A digital computer stores information as
numbers, but those numbers are not stored
as decimal numbers.



All information in a computer is stored and
managed as binary values.
The binary number system has only two digits,
0 and 1.
A single binary digit is called a bit.
8
Converting Binary Numbers
to Decimal Numbers
 Starting with the rightmost bit in a binary number,




each position represents a power of 2, with the
rightmost bit position representing 20 which is decimal
1, the next bit position representing 21 which is 2 and
the next representing 22 which is 4, etc.
Binary 1011 is 1* 23 or 8, plus 0 * 22 or 0, plus 1 * 21
or 2 plus 1 * 20 or 1 which adds up to 11 decimal.
Binary 11001001 is 201 decimal.
In general, N bits can represent 2N unique items.
Computers typically manipulate sequences of 8 bits
with each sequence of 8 bits referred to as a byte.
9
Hardware Components
 We use the term computer architecture to describe
how the hardware components of a computer are put
together.
 A program and its data reside in main memory
while the program runs.



The Central Processing Units (CPU) reads one
program instruction from main memory and executes it.
If an instruction needs data, such as the amount in a
bank account, the CPU reads that information as well.
The process repeats until the program ends.
10
Peripherals
 Almost all devices in a computer other than
the CPU and main memory are called
peripherals.


Controllers are devices that coordinate the
activities of specific peripherals.
Input/Output (I/O) devices and secondary
memory devices are considered peripherals.
11
Input/Output Devices
 For our purposes, the primary I/O devices will
be the keyboard and the monitor.


Output on a monitor is achieved by breaking
the screen picture into small pieces called
picture elements (pixels). The pixels are
represented in the computer as numbers (as is
everything else).
A typical monitor can display a grid of 1280 x
1024 pixels.
12
Main Memory and Secondary
Memory
 Main memory is made up of a series of small,
consecutive memory locations.


Associated with each memory location is a unique
number called an address.
On many computers, each memory location consists of
8 bits, or one byte of information.
 The storage capacity of a device such as main
memory is the total number of bytes it can hold.


A kilobyte (KB)is 1,024 bytes or 210 bytes.
Larger units are a megabyte (MB), a gigabyte (GB),
and a terabyte (TB).
 It is usually easier to think about these capacities by
rounding them off.
13
Characteristics of Main Memory
 When data is stored in a main memory
location, it overwrites (thus destroying) any
information that was previously stored there.
 Main memory is usually volatile.


The information stored in it will be lost if its
electrical power is turned off.
You should frequently save your work onto a
secondary memory device such as a disk in
case the power goes off.
14
Secondary Memory Devices
 A disk is a direct access (also referred to as
random access) device since the read/write
head can move very quickly to the
information needed.
 A tape must be rewound or fast-forwarded to
get to the desired information.

A tape is therefore considered a sequential
access device.
15
Two Other Common Terms
for Memory Devices
 Random Access Memory (RAM)
 The terms RAM and main memory are basically
interchangeable.
 RAM should probably be called read-write memory
since data can be both written to it and read from it.
 Read-Only Memory (ROM)
 After information is stored on ROM, it cannot be altered
(easily).
 ROM chips are often embedded into the main circuit
board to provide the preliminary instructions when the
computer is initially turned on.
16
Other Memory Devices
 Additional memory devices include CD-ROM,
CD-Recordable (CD-R) drives, CD Rewritable
(CD-RW) discs, and DVD devices.

The speed of a CD drive is expressed in
multiples of x, which represents a data transfer
speed of 153,600 bytes per second.
 Due to improvements in technology, storage
capacity approximately doubles every 18
months.
17
Networks
 A network is two or more computers
connected together so they can exchange
information.


Each computer of a network has its own
network address.
One technique to improve network speed is to
divide large messages into segments, called
packets.

Then send the individual packets across the
network intermixed with pieces of other
messages sent by other users.
18
Local Area Networks and
Wide Area Networks
 A local-area network (LAN) is designed to
span short distances and connect a relatively
small number of computers.
 A wide-area network (WAN) connects two or
more LANs, often across long distances.

LANs connected by a WAN are often owned
by different companies or organizations, and
might even be located in different countries.
19
The Internet
 The Internet is a network of networks.
 A protocol is a set of rules that governs how
two things communicate.

The software that controls the movement of
messages across the Internet must conform to
a set of protocols called TCP/IP for
Transmission Control Protocol/Internet
Protocol.
 Every computer connected to the Internet
has an IP address that uniquely identifies it
among all other computers on the Internet.
20
IP Address vs Internet Address
 An IP address is of the form 204.192.116.2.
 Fortunately, the Internet allows each
computer to be given a unique name which is
often referred to as its Internet Address.


The first part of an Internet Address is the
local name of a specific computer.
The rest of the name is the domain name.
 The computer you will be using in this course
is osprey.unf.edu.

edu is the domain name.
21
The Domain Name System
 The Internet uses another software program,
the Domain Name System (DNS) to
translate an Internet Name to its
corresponding IP Address.

Each organization connected to the Internet
operates a domain server that maintains a list
of all computers in the organization and their
IP addresses.

If the local domain server does not have the IP
address for a name, it contacts another domain
server that does.
22
The World Wide Web
 The World Wide Web (also known as WWW
or simply the Web) makes the exchange of
information easy.


Web software provides a common interface
through which many different types of
information can be accessed with the click of a
mouse.
The Web is based on the concepts of
hypertext and hypermedia.

Hypermedia incorporates graphics, sound,
animations, and video.
23
Hypertext and Browsers
 Hypertext is a way to organize information so
that the flow of ideas is not constrained to a
linear progression.

Documents are linked at various points
according to natural relationships so that the
reader can jump from one document to
another, following the appropriate path for that
reader’s needs.
 Browsers allow documents to be formatted
using the HyperText Markup Language
(HTML).
24
Uniform Resource Locators
 Information on the Web is found by identifying a
Uniform Resource Locator (URL)




A URL uniquely specifies documents and other
information for a browser to obtain and display.
 An example URL is http://www.unf.edu
The first piece of a URL is a protocol (HyperText
Transfer Protocol – HTTP in this example) which
determines the way the browser should communicate.
The second piece is the Internet address of the
machine on which the document is stored.
A possible third piece of information is the file name of
the file you wish to view.
25
Another Sample URL
 http://www.unf.edu/campus
 In this URL, the protocol is http (HyperText Transfer
Protocol).
 The machine referenced is www (a web server found
at unf.edu)
 The information is stored in a file named campus.
 The Internet vs the World Wide Web
 The Internet makes it possible to communicate via
computers around the world.
 The Web makes that communication a straightforward
and enjoyable activity.
 The Web can be used on a LAN or even a single machine
that is not connected to any network.
26
Programming
 The rest of this course explores the process
of creating programs using Java.

All of the software we have discussed
including the Internet and Web protocols are
programs that some programmer has written.
 This section discusses the purpose of
programming in general and introduces the
Java Programming Language.
27
Problem Solving

The purpose of writing a program is to solve a
problem. Problem solving consists of multiple
steps:
1.
2.
3.
4.
5.
6.
Understanding the problem.
Breaking the problem into manageable pieces.
Designing a solution.
Considering alternatives to the solution and refining
the solution.
Implementing the solution.
Testing the solution and fixing any problems that
exist.
28
How do these Steps Apply to You?
 By the time you complete a degree in Computer and
Information Sciences you will have experienced all of
these problem solving steps and practiced them
often.
 In this course, the emphasis is on learning
programming and much of the other work is done for
you.

However, you should be aware that even for beginning
students who are assigned a problem and provided a
lot of information, the most common mistake is to begin
coding before you have put some thought into
understanding the problem and designing a solution.
29
The Java Programming Language
 A programming language defines a set of
rules:

That determine exactly how a programmer can
combine words and symbols of the language
into programming statements.


Programming statements are the instructions
that are carried out when the program is
executed.
Java is an object-oriented programming
language.

Java is one of the fastest growing programming
technologies of all time.
30
Reasons Why Java is Popular
 Java is the first programming language to
deliberately embrace the concept of writing
programs that can be executed on the Web.
 The Java language is accompanied by a
library of extra software that we can use
when developing programs.

The library provides the ability to create
graphics, communicate over networks, and
interact with databases.

The set of supporting libraries is huge and
versatile.
31
A Java Program
 See Lincoln.java on page 30.
/* Lewis/Loftus
6/11/2003
Lincoln.java demonstrates the basic structure of a Java Application.
*/
public class Lincoln
{
// Prints a presidential quote.
public static void main (String[ ] args)
{
System.out.println (“A quote by Abraham Lincoln:“);
System.out.println (“Whatever you are, be a good one.”);
}
}
32
What to Notice in Lincoln.java
 The first few lines between /* and */ are
comments.




Comments don’t affect what the program
does but are included to make the program
easier to understand.
Comments included in a program are called
inline documentation.
The comment symbols /* and */ can surround
a multiline comment.
The comment symbol // can be used at the
beginning of a single-line comment.
33
What to Notice (2)
 The rest of the Lincoln.java program is a
class name and a class definition.


This class name is Lincoln.
The class definition runs from the first
opening brace { to the final closing brace }.


Inside the class definition is a single-line
comment describing the purpose of the main()
method.
A method is a group of programming
statements that are given a name (main).
34
The println() Method
 The two lines of code in the main() method invoke
another method called println() (pronounced print
line).



Our program must invoke, or call, a method at the
point where we want the method to execute.
The println() method prints the specified characters to
the screen.
 The characters to be printed are represented as a
character string, enclosed in double quote characters
(“The string you want to print. “).
The code for the println() method definition is in a
library. We just need to call the println() method and
pass it the String you want to display.
35
Another Look at Lincoln.java
 See the Lincoln
/* Lewis/Loftus
program on page 30.
6/11/2003
Lincoln.java demonstrates the basic structure of a Java Application.
*/
// The next line names the class and the { begins the class definition
public class Lincoln // The class name is the same as the file name, but
{
// without the .java extension.
// Prints a presidential quote.
public static void main (String[] args) // This line is the method header
{ // The method body starts with the left bracket.
// The println() method is found in the System class in a Java library
System.out.println(“A quote by Abraham Lincoln:“);
System.out.println(“Whatever you are, be a good one.”);
}
}
36
The Method Named main()
 All java applications have a method named main.



This is where processing begins for every application
program.
The main method definition in Java is always preceded by
the words public, static, and void.
Each programming statement in the main method is
executed, one at a time in order, until the end of the method
is reached.
 Some of the statements in the main method may call another


method. If so, that method executes and control then returns to
the next statement in main.
After the last statement in main executes, the program
terminates.
The use of String and args will be explained later.
37
Comments
 Comments are notes entered into the text of
a program to assist that programmer or any
other programmer who must later modify or
simply understand the code.

The original programmer probably will not
remember later the details of the program he
or she has written.
 Comments within the text of a program are
referred to as internal documentation.

Good internal and external documentation
are both essential.
38
Two Types of Comments
 A single-line comment in Java takes the form:
 // This is a comment.
 A multi-line comment takes the form:
/*
This is one comment
that spans several lines.
*/
 It is also permissible to use the above notation
for a single-line comment.
/* This is a comment */
39
External Documentation
javadoc
 The Java SDK (Software Development Kit) also
specifies a means of creating external documentation
using a software tool called javadoc . Here is how it
works:


If you place a second asterisk following the /* at the
beginning of a comment, the content of the comment
can be used to automatically generate external
documentation about your program using a tool called
javadoc .
Example: /** javadoc will print this comment
for use as external documentation.
*/
40
Good Programming Practices
 Appendix G of our text presents guidelines for good
programming practices and includes specific
techniques for documenting programs.



You can assume the reader is computer literate and
familiar with Java.
However, you must assume the reader knows almost
nothing about what the program is supposed to do.
A section of code that seems intuitive to you when you
write it might not seem so to another reader or to
yourself later.
 You will be expected to apply the coding guidelines in
Appendix G (starts on page 705) as you write your
programs.
41
Identifiers and Reserved Words
 The words used when writing programs are called
identifiers.

There are three categories of identifiers:
1. Words that we make up (Lincoln and args in demo
program 1.1)
2. Words that another programmer chose (String,
System, out, println, and main).

3.
Often these are words that were chosen by a programmer
who wrote code that became part of a Java library and
are now available for use by all Java programmers.
Words that are reserved for special purposes in the
language (class, public, static, and void).

The designers of the Java language chose these
words.
42
The Reserved Words

Reserved words are identifiers that have special meaning in a programming
language.

In the Lincoln program, they are class, public, static, and void.
//********************************************************************
// Lincoln.java
Author: Lewis/Loftus
//
// Demonstrates the basic structure of a Java application.
//********************************************************************
public class Lincoln
{
//----------------------------------------------------------------// Prints a presidential quote.
//----------------------------------------------------------------public static void main (String[] args)
{
System.out.println ("A quote by Abraham Lincoln:");
System.out.println ("Whatever you are, be a good one.");
}
}
43
Reserved Words
 The Java reserved words – these words cannot be used for
any other purpose, such as naming a class or method.
abstract
boolean
break
byte
case
catch
char
class
const
continue
default
do
double
else
extends
false
final
finally
float
for
goto
if
implements
import
instanceof
int
interface
long
native
new
null
package
private
protected
public
return
short
static
strictfp
super
switch
synchronized
this
throw
throws
transient
true
try
void
volatile
while
44
Rules for Naming Identifiers
 An identifier that we create for use in a
program can be composed of any
combination of letters, digits, the
underscore character ( _ ), and the dollar
sign ($), but it cannot begin with a digit.
 Java is case sensitive, which means that two
identifier names that differ only in the case of
their letters are considered to be different
identifiers.

Total, Total, ToTaL, and TOTAL are all different
identifiers.
45
Conventions for Naming Identifiers
 Using a consistent case format for each kind of
identifier makes the different kinds of identifiers
easier to distinguish.



Title case (uppercase for the first letter of each word)
is conventional for class names.
 Example: GraduateStudent
Lowercase is used for the first letter of method
names and variable names. However, the first letter
of each additional word that is part of the identifier is
capitalized.
 Example: payRate
Appendix G presents guidelines for naming identifiers.
 You are to follow those guidelines in your programs.
46
Choosing Identifier Names
 Identifier names should be descriptive but
not verbose.

Avoid meaningless names such as a or x.


Unless the name is actually descriptive, such as
using x and y to represent (x, y) coordinates.
Avoid using unnecessarily long names.
 A “name” in Java is a series of identifiers
separated by the dot (period) character.

The name System.out is the way we
designate the object through which we invoke
the println method.
47
White Space
 White space consists of blanks, tabs, and newline
characters.


White space is used to separate the words and
symbols used in Java programs.
A programmer can use white space to emphasize parts
of the program and to make the program easier to
read.
 Except when it’s used to separate words, the
computer ignores white space.


This gives programmers great flexibility in how they
format a program.
The guidelines in Appendix G discuss the appropriate
use of white space.
48
Programming Languages
 Programming languages are often
categorized into the following four groups:
1.
2.
3.
4.
Machine Language
Assembly Language
High-Level Languages
Fourth-Generation Languages
 In order for a program to run on a computer,
it must be expressed in that computer’s
machine language.

Each type of CPU has its own language.
49
From Machine Language
to Assembly Language
 Each machine language instruction can
accomplish only one simple task.

For example, copy a value into a register or
compare two values.
 Machine language code is expressed as a
series of binary digits and is extremely
difficult for humans to read and write.

This gave rise to Assembly Language, which
replaced binary digits with mnemonics, short
English-like words that represent commands
or data.
50
From Low-level Languages
to High-level Languages
 Both assembly language and machine language
are considered low-level languages.

Generally, each assembly language instruction
corresponds to an equivalent machine language
instruction.
 Today most programmers use a high-level language
to write software.


A high-level language is expressed in English-like
phrases, approaching natural language.
A single high-level language programming statement
can accomplish the equivalent of many – perhaps
hundreds – of machine language instructions.
51
Fourth-Generation Languages
 Some programming languages operate at an
even higher level.

They might include automatic report
generation or interaction with a database.
 These languages are called fourth-
generation languages, or simply 4GLs,
because they followed the first three
generations of computer programming:
machine, assembly, and high-level.
52
Compilers and Interpreters
 Initially, you will use an editor as you type a
program into a computer and store it in a file.



The editor you will use will be either vi or pico.
Each time you need to make a change to the
code in your program, you “open” the program
in an editor.
After editing and saving your program, you
attempt to translate it from high-level code
into a form that can be executed.

The translation may result in errors, in which
case you return to the editor to make changes to
the code to fix the problem.
53
Editing and Running Your Program
 Once the translation occurs successfully, you
can execute the program and evaluate the
results.

If your results are not what you want (or if you
want to enhance your existing program), you
again return to the editor to make changes.
errors
Edit and
Save Program
Translate Program
into Executable Form
errors
Execute Program
and Evaluate Results
54
Translation of Source Code
 The translation of source code into
(ultimately) machine language for a particular
type of CPU can occur in a variety of ways.



By using a compiler.
By using an interpreter.
By using both a compiler and interpreter

This is how Java does it.
55
A Compiler
 A compiler is a program that translates code
in one language to an equivalent code in
another language.



The original code is called source-code.
The language into which it is translated is
called the target language.
For many traditional compilers, the source
code is translated directly into a particular
machine language.

In that case, the translation process occurs once
and the resulting executable program can be run
whenever needed.
56
An Interpreter
 An interpreter is similar to a compiler but has an
important difference.


An interpreter interweaves the translation and
execution activities.
 A small part of the source code, such as one
statement, is translated and executed.
 Then another part is translated and executed, and so
on.
This eliminates the need for a separate compilation
phase; however, the program runs more slowly
because the translation process occurs during each
execution.
 Each statement is translated, then executed
immediately, rather than translating the entire program
and then executing the translated code.
57
Java Uses Both a
Compiler and Interpreter
 The Java compiler translates Java source
code into Java bytecode.

Bytecode is a representation of the program
in a low-level code similar to machine
language code.
 The Java interpreter reads a short segment
of Java bytecode, translates that segment
into machine language and executes it.
This process is repeated as the program
executes.
58
The Advantage of Java Bytecode
 The difference between Java bytecode and
true machine language code is that Java
bytecode is not tied to any particular
processor type.

This makes Java architecture neutral, and
therefore easily portable from one machine to
another.

All you need is a Java interpreter or bytecode
compiler for each processor type on which the
bytecode is to be executed.
59
Compiling and Executing Programs
on Osprey

Assume you want to write the Lincoln.java program and
execute it on Osprey.

At the Linux $ prompt you will create your source code by
entering either:
$
$

pico Lincoln.java or
vi Lincoln.java
Once you have saved your source code, you compile
your source code by entering at the $ prompt:
$ javac Lincoln.java


Correct any errors the compiler finds.
When you have a successful compile, you will translate
your bytecode (execute your program) by entering at the
$ prompt:
$ java Lincoln
60
The Java Software Development Kit
(JDK)
 The Java compiler and interpreter are part of the
Java Software Development Kit (Java SDK or just
JDK).


The JDK can be downloaded for free from the Sun
Microsystem Web site ( java.sun.com ) or from our
text’s website
http://duke.csc.villanova.edu/jss1/javaResources/sdk.js
p.
Note: the standard JDK tools are executed on the
command line and do not include an editor. The JDK
is already on osprey, so you do not need to
download it.
 Any editor that can save a document as a simple text
file can be used. We will use pico or vi initially.
61
Integrated Development
Environments (IDEs)
 IDEs combine an editor, compiler, and other
Java support tools into a single program.

There are many IDEs including Borland’s
JBuilder and Xinox Software’s JCreator.
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Syntax and Semantics
 Each programming language has its own
unique syntax.


The syntax rules of a language dictate exactly
how the vocabulary elements of the language
can be combined to form statements.
During compilation, all syntax rules are
checked.

If a program is not syntactically correct, the
compiler will issue error messages and will
not produce bytecode.
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Java Syntax
 Java has a similar syntax to C and C++.


However, beyond the basic syntax issues,
there are many important differences between
Java and these languages.
Appendix I contains a summary of the
differences between Java and C++.
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Semantics
 The semantics of a statement in a
programming language define what will
happen when that statement is executed.


Programming languages are generally
unambiguous, which means that there is one
and only one interpretation for each statement.
The same exact English sentence can have
multiple valid meanings.

A computer language cannot allow such
ambiguities to exist.
65
Errors
 You will encounter three kinds of errors as
you develop programs:
1.
2.
3.
Compile-time errors
Runtime errors
Logical errors
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Compile-time and Run-time Errors
 An error identified by the compiler is called a
compile-time error.


If a compile-time error occurs, an executable version of
the program is not created.
Use your editor to correct the error, then recompile
your program.
 A runtime error causes the program to terminate
abnormally during execution.


An example is an attempt to divide by zero.
In Java, many runtime errors are represented as
exceptions that can be caught and dealt with (covered
in Chapter 8).
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Logical Errors
 When your program has a logical error, it will
compile and execute, but produces incorrect
results.


A logical error occurs when a value is
calculated incorrectly.
A programmer must test the program
thoroughly, comparing the expected results to
those that actually occur.

The process of finding and correcting defects in a
program is called debugging.
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