Transcript Introduction to computer systems, Java

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CSI 1102
Introduction to Software Design
Prof. Dr.-Ing. Abdulmotaleb El Saddik
University of Ottawa (SITE 5-037)
(613) 562-5800 x 6277
elsaddik @ site.uottawa.ca
abed @ mcrlab.uottawa.ca
http://www.site.uottawa.ca/~elsaddik/
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Learning objectives
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•
Brief review of the basic computer processing
concepts
•
Understand what problem solving entails
•
Understand why problem solving skills are so
important
•
Describe the various levels of programming
languages
•
Understand a first Java program and its basic
structure
•
Source: Sections 1.3-1.5, Chapter 1 (L&L)
A brief review of
Networking
Read through Sections 1.0-1.2 to ensure
you are “up to date”
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PC Penetration Worldwide
1400
1200
Millions
1000
800
PC's
Population
600
400
200
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Ch
in
a
ia
In
d
an
y
Ge
rm
Fr
an
ce
UK
US
A
0
Sources: IDC, UN
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Hardware and Software
Hardware
• the physical, tangible parts of a computer
• keyboard, monitor, disks, wires, chips, etc.
Software
• programs and data
• a program is a series of instructions
A computer requires both hardware and software
Each is essentially useless without the other
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Software Categories
Operating System
• controls all machine activities
• provides the user interface to the computer
• manages resources such as the CPU and
memory
• Windows XP, Windows 2000, Unix, Linux, Mac
OS
Application program
• generic term for any other kind of software
• word processors, missile control systems, games
Most operating systems and application programs
have a graphical user interface (GUI)
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Networks
A network is two or more computers that are
connected so that data and resources can be
shared
Most computers are connected to some kind of
network
Each computer has its own network address, which
uniquely identifies it among the others
A file server is a network computer dedicated to
storing programs and data that are shared among
network users
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Network Connections
Each computer in a network could be directly
connected to every other computer in the network
These are called point-to-point connections
Adding a computer requires
a new communication line
for each computer already
in the network
This technique is not practical for
more than a few close machines
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Network Connections
Most networks share a single communication line
Adding a new computer to the network is relatively
easy
Network traffic must take
turns using the line, which
introduces delays
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Often information is broken
down in parts, called packets,
which are sent to the receiving
machine and then reassembled
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Local-Area Networks
A Local-Area Network
(LAN) covers a small
distance and a small
number of computers
LAN
A LAN often connects the machines
in a single room or building
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Wide-Area Networks
A Wide-Area Network (WAN)
connects two or more LANs,
often over long distances
LAN
LAN
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A LAN usually is owned
by one organization, but
a WAN often connects
groups in different
countries
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The Internet
The Internet is a WAN which spans the entire planet
The word Internet comes from the term
internetworking, which implies communication
among networks
It started as a United States government project,
sponsored by the Advanced Research Projects
Agency (ARPA) - originally it was called the
ARPANET
The Internet grew quickly throughout the 1980s and
90s
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Less than 600 computers were connected to the
Internet in 1983; by the year 2000 there were over
10 million
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The World Wide Web
The World Wide Web is just ONE application of the Internet
• allows many different types of information to be accessed using
a common interface
A browser is a program which accesses and presents
information
• text, graphics, video, sound, audio, executable programs
A Web document usually contains links to other Web
documents, creating a hypermedia environment
The term Web comes from the fact that information is not
organized in a linear fashion
Other Internet applications:
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• E-mail, Telnet, FTP, etc…
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The World Wide Web
Web documents are often defined using the
HyperText Markup Language (HTML)
Information on the Web is found using a Uniform
Resource Locator (URL):
http://www.uottawa.ca
http://www.site.uottawa.ca/index.html
ftp://java.sun.com/applets/animation.zip
A URL indicates a protocol (http), a domain, and
possibly specific documents
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700
600
Millions of Users
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People on the Internet (Worldwide)
500
400
Outside US
North America
300
200
100
03
20
02
20
01
20
00
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99
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Source: IDC
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Programming &
Programming Languages
Source: Sections 1.3-1.5, Chapter 1 (L&L)
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So what is Problem Solving?
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The purpose of writing a program is to solve a
problem
The general steps in problem solving are:
•
•
•
•
•
•
Understand the problem
Dissect the problem into manageable pieces
Design a solution
Consider alternatives to the solution and refine it
Implement the solution
Test the solution and fix any problems that exist
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Problem Solving: “Divide and Conquer”
Many software projects fail because the developer
didn't really understand the problem to be solved
We must avoid assumptions and clarify ambiguities
As problems and their solutions become larger, we
must organize our development into manageable
pieces: “Divide and Conquer”
 This technique is fundamental to software
development
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Object-oriented approach to Problem Solving
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We will dissect our solutions into pieces called classes
and objects, taking an object-oriented approach
“If you want to eat an elephant,
take one bite at a time”.
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Problem solving through a programming language
So suppose we have a problem to be solved
We choose to design and implement a computer program to
solve the problem
We use a programming language to do the job for us
A programming language
• specifies the words and symbols that we can use to write a
program
• employs a set of rules that dictate how the words and symbols
can be put together to form valid program statements
Examples of programming languages:
• Fortran, Cobol, C++, C, Delphi, Pascal, Smalltalk and JAVA
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Different Programming Language Levels
There are four programming language levels:
• machine language
• assembly language
• high-level language
• fourth-generation language
Each type of CPU has its own specific machine
language
The other levels were created to make it easier for a
human being to read and write programs
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Basic Program Development
Edit and
save program
errors
errors
Compile program
Execute program and
evaluate results
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Problem solving using JAVA
The Java programming language was created by
Sun Microsystems, Inc.
It was introduced in 1995 and it's popularity has
grown quickly since
It is an object-oriented language
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Java Program Structure
In the Java programming language:
• A program is made up of one or more classes
• A class contains one or more methods
• A method contains program statements
These terms will be explored in detail throughout
the course, starting from next week
A Java application always contains a method called
main
See Lincoln.java (page 30)
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Java Program Structure
//
comments about the class
public class MyProgram
{
class header
class body
Comments can be added almost anywhere
}
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Java Program Structure
//
comments about the class
public class MyProgram
{
//
comments about the method
public static void main (String[] args)
{
method body
}
}
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method header
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Lincoln.java
//***********************************************************
***
// Lincoln.java
Author: Lewis and 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.");
}
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}
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About programming language:
They all have the following in common
Basic Components
• Comments
• Identifiers
• (Reserved Words)
• Symbols (e.g. <, >, =, …)
• White Spaces
Syntax and Semantics
Translation
Errors
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What are Comments?
Comments in a program are called inline
documentation
They should be included to explain the purpose of
the program and describe processing steps
They do not affect how a program works
Java comments can take three forms:
// this comment runs to the end of the line
/*
this comment runs to the terminating
symbol, even across line breaks
/** this is a javadoc comment
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*/
*/
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The Importance of Comments
Describe WHAT, WHY, HOW and by WHOM
Very important for further use
• To understand years from now
• Developer’s turnover high
Do not add them at the end!!!!
Without comments is very difficult to maintain code
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Lincoln.java
//***********************************************************
// Lincoln.java
Author: Lewis and Loftus
//
// Demonstrates the basic structure of a Java application.
//***********************************************************
Comments
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.");
}
}
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Identifiers
Identifiers are the words a programmer uses in a
program
An identifier can be made up of letters, digits, the
underscore character ( _ ), and the dollar sign
Identifiers cannot begin with a digit
Java is case sensitive - Total, total, and
TOTAL are different identifiers
By convention, Java programmers use different
case styles for different types of identifiers, such
as
• title case for class names - Lincoln
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• upper case for constants - MAXIMUM
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Identifiers
Sometimes we choose identifiers ourselves when
writing a program (such as Lincoln)
Sometimes we are using another programmer's
code, so we use the identifiers that they chose
(such as println)
Often we use special identifiers called reserved
words that already have a predefined meaning in
the language
• A reserved word cannot be used in any other way
• E.g. IF (temp < 30) THEN
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Reserved Words
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The Java reserved words:
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
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About Syntax and Semantics
The syntax rules of a language define how we can
put together symbols, reserved words, and identifiers
to make a valid program
E.g. if (height > tallest) then
{
tallest = height;
}
The semantics of a program statement define what
that statement means (its purpose or role in a
program)
E.g. We want to determine the tallest person.
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About Syntax and Semantics
A program that is syntactically correct is not
necessarily logically (semantically) correct
A program will always do what we tell it to do, not
what we meant to tell it to do !!!
Typical error  incorrect boundaries
E.g. (height > tallest)
instead of
(height >= tallest)
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What are White Spaces?
Spaces, blank lines, and tabs are called white
space
White space is used to separate words and
symbols in a program
Extra white space is ignored
A valid Java program can be formatted in many
ways
Programs should be formatted to enhance
readability, using consistent indentation
• See Lincoln2.java (page 37)
• See Lincoln3.java (page 38)
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A BADLY structured Java example
//***************************************************
//
Lincoln2.java
Author: Lewis and Loftus
//
//
Demonstrates a poorly formatted, though valid, program.
//*********************************************************
public class Lincoln2{public static void main(String[]args){
System.out.println("A quote by Abraham Lincoln:");
System.out.println("Whatever you are, be a good one.");}}
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Lincoln3.java
//********************************************************************
// Lincoln3.java
Author: Lewis and Loftus
//
// Demonstrates another valid program that is poorly formatted.
//********************************************************************
public
Lincoln3
class
{
public
static
void
main
(
String
[]
args
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)
{
System.out.println
(
"A quote by Abraham Lincoln:"
)
;
System.out.println
(
"Whatever you are, be a good one."
)
;
}
}
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Translation of Programming Languages
A program must be translated into machine language
before it can be executed on a particular type of
CPU
This can be accomplished in several ways
A compiler is a software tool which translates
source code into a specific target language
Often, that target language is the machine language
for a particular CPU type
The Java approach is somewhat different
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Translation in Java
Java source
code
Java
compiler
Java
bytecode
Java
interpreter
Bytecode
compiler
Machine
code
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Java
Compiling:
•javac <Identifier.java>
• javac Lincoln.java
•You will get: Lincoln.class
Executing:
•java <Identifier>
• java Lincoln
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Java Translation
The Java compiler translates Java source code into
a special representation called bytecode
Java bytecode is not the machine language for any
traditional CPU
Another software tool, called an interpreter,
translates bytecode into machine language and
executes it
Therefore the Java compiler is not tied to any
particular machine
Java is considered to be architecture-neutral
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About Errors
A program can have three types of errors
• The compiler will find syntax errors and other basic
problems (compile-time errors)
• If compile-time errors exist, an executable version
of the program is not created
• A problem can occur during program execution, such
as trying to divide by zero, which causes a program
to terminate abnormally (run-time errors)
• A program may run, but produce incorrect results,
perhaps using an incorrect formula (logical errors)
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Creating your program: Java Development Environments
•
•
•
•
•
•
•
•
Sun Java Development Kit (JDK)
Sun Forte for Java
Borland JBuilder
MetroWerks CodeWarrior
Microsoft Visual J++
Symantec Café
Monash BlueJ
RealJ (www.realj.com)  Used in Lab B02
Though the details of these environments differ, the
basic compilation and execution process is
essentially the same
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Introduction to Graphics
The last one or two sections of each chapter of the
textbook focus on graphical issues
Most computer programs have graphical
components
A picture or drawing must be digitized for storage
on a computer
A picture consists of pixels, and each pixel is
stored separately
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Representing Color
A black and white picture can be stored using one
bit per pixel (0 = white and 1 = black)
A colored picture requires more information; there
are several techniques for representing colors
For example, every color can be represented as a
mixture of the three additive primary colors Red,
Green, and Blue
In Java, each color is represented by three
numbers between 0 and 255 that collectively are
called an RGB value
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Coordinate Systems
Each pixel can be identified using a twodimensional coordinate system
When referring to a pixel in a Java program, we use
a coordinate system with the origin in the top-left
corner
(0, 0)
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(112, 40)
Y
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X
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Summary of Lecture
Lecture has focused on programming and
programming languages
Students should now
Understand what problem solving entails
Understand why problem solving skills are so important
Describe the various levels of programming
languages
Understand a first Java program and its basic
structure
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