Chapter 1: Computer Systems
Chapter 1: Computer Systems
Presentation slides for
Presentation slides for
Java Software Solutions
Java Software Solutions
Foundations of Program Design
Foundations of Program Design
Second Edition
Second Edition
by John Lewis and William Loftus
by John Lewis and William Loftus
Java Software Solutions is published by Addison-Wesley
Java Software Solutions is published by Addison-Wesley
Presentation slides are copyright 2000 by John Lewis and William Loftus. All rights reserved.
Presentation slides are copyright 2000 by John Lewis and William Loftus. All rights reserved.
Instructors using the textbook may use and modify these slides for pedagogical purposes.
Instructors using the textbook may use and modify these slides for pedagogical purposes.
2
Focus of the Course
Focus of the Course
Object-Oriented Software Development
Object-Oriented Software Development
•
problem solving
problem solving
•
program design and implementation
program design and implementation
•
object-oriented concepts
object-oriented concepts
–
objects
objects
–
classes
classes
–
interfaces
interfaces
–
inheritance
inheritance
–
polymorphism
polymorphism
•
graphics and Graphical User Interfaces
graphics and Graphical User Interfaces
•
the Java programming language
the Java programming language
3
Computer Systems
Computer Systems
We first need to explore the fundamentals of
We first need to explore the fundamentals of
computer processing
computer processing
Chapter 1 focuses on:
Chapter 1 focuses on:
•
components of a computer
components of a computer
•
how those components interact
how those components interact
•
how computers store and manipulate information
how computers store and manipulate information
•
computer networks
computer networks
•
the Internet and the World-Wide Web
the Internet and the World-Wide Web
•
programming and programming languages
programming and programming languages
•
graphic systems
graphic systems
4
Hardware and Software
Hardware and Software
Hardware
Hardware
•
the physical, tangible parts of a computer
the physical, tangible parts of a computer
•
keyboard, monitor, wires, chips, data
keyboard, monitor, wires, chips, data
Software
Software
•
programs and data
programs and data
•
a
a
program
program
is a series of instructions
is a series of instructions
A computer requires both hardware and
A computer requires both hardware and
software
software
Each is essentially useless without the other
Each is essentially useless without the other
5
CPU and Main Memory
CPU and Main Memory
Central
Processing
Unit
Main
Memory
Chip that
Chip that
executes
executes
program
program
commands
commands
Intel Pentium III
Intel Pentium III
Sun Sparc
Sun Sparc
Processor
Processor
Primary storage
Primary storage
area for
area for
programs and
programs and
data that are in
data that are in
active use
active use
Synonymous with
Synonymous with
RAM
RAM
6
Secondary Memory Devices
Secondary Memory Devices
Floppy Disk
Hard Disk
Main
Memory
Central
Processing
Unit
Secondary memory
Secondary memory
devices provide
devices provide
long-term storage
long-term storage
Information is moved
Information is moved
between main memory
between main memory
and secondary memory
and secondary memory
as needed
as needed
Hard disks
Hard disks
Floppy
Floppy
disks
disks
ZIP disks
ZIP disks
Writable
Writable
CDs
CDs
Tapes
Tapes
7
Input / Output Devices
Input / Output Devices
Monitor
Keyboard
Main
Memory
Central
Processing
Unit
Floppy Disk
Hard Disk
I/O devices allow user
I/O devices allow user
interaction
interaction
Monitor screen
Monitor screen
Keyboard
Keyboard
Mouse
Mouse
Bar code scanner
Bar code scanner
Light pen
Light pen
Touch screen
Touch screen
8
Software Categories
Software Categories
Operating System
Operating System
•
controls all machine activities
controls all machine activities
•
provides the user interface to the computer
provides the user interface to the computer
•
manages resources such as the CPU and memory
manages resources such as the CPU and memory
•
Windows 98, Windows NT, Unix, Linux, Mac OS
Windows 98, Windows NT, Unix, Linux, Mac OS
Application program
Application program
•
generic term for any other kind of software
generic term for any other kind of software
•
word processors, missile control systems, games
word processors, missile control systems, games
Most operating systems and application
Most operating systems and application
programs have a graphical user interface
programs have a graphical user interface
(GUI)
(GUI)
9
Analog vs. Digital
Analog vs. Digital
There are two basic ways to store and manage
There are two basic ways to store and manage
data:
data:
Analog
Analog
•
continuous, in direct proportion to the data represented
continuous, in direct proportion to the data represented
•
music on a record album - a needle rides on ridges in the
music on a record album - a needle rides on ridges in the
grooves that are directly proportional to the voltage sent
grooves that are directly proportional to the voltage sent
to the speaker
to the speaker
Digital
Digital
•
the information is broken down into pieces, and each
the information is broken down into pieces, and each
piece is represented separately
piece is represented separately
•
music on a compact disc - the disc stores numbers
music on a compact disc - the disc stores numbers
representing specific voltage levels sampled at various
representing specific voltage levels sampled at various
points
points
10
Digital Information
Digital Information
Computers store all information digitally:
Computers store all information digitally:
•
numbers
numbers
•
text
text
•
graphics and images
graphics and images
•
audio
audio
•
video
video
•
program instructions
program instructions
In some way, all information is
In some way, all information is
digitized
digitized
-
-
broken down into pieces and represented as
broken down into pieces and represented as
numbers
numbers
11
Representing Text Digitally
Representing Text Digitally
For example, every character is stored as a
For example, every character is stored as a
number, including spaces, digits, and
number, including spaces, digits, and
punctuation
punctuation
Corresponding upper and lower case letters
Corresponding upper and lower case letters
are separate characters
are separate characters
H i , H e a t h e r .
H i , H e a t h e r .
72 105 44 32 72 101 97 116 104 101 114 46
72 105 44 32 72 101 97 116 104 101 114 46
12
Binary Numbers
Binary Numbers
Once information is digitized, it is represented
Once information is digitized, it is represented
and stored in memory using the
and stored in memory using the
binary number
binary number
system
system
A single binary digit (0 or 1) is called a
A single binary digit (0 or 1) is called a
bit
bit
Devices that store and move information are
Devices that store and move information are
cheaper and more reliable if they only have to
cheaper and more reliable if they only have to
represent two states
represent two states
A single bit can represent two possible states, like
A single bit can represent two possible states, like
a light bulb that is either on (1) or off (0)
a light bulb that is either on (1) or off (0)
Combinations of bits are used to store values
Combinations of bits are used to store values
13
Bit Combinations
Bit Combinations
1 bit
1 bit
0
0
1
1
2 bits
2 bits
00
00
01
01
10
10
11
11
3 bits
3 bits
000
000
001
001
010
010
011
011
100
100
101
101
110
110
111
111
4 bits
4 bits
0000
0000
0001
0001
0010
0010
0011
0011
0100
0100
0101
0101
0110
0110
0111
0111
1000
1000
1001
1001
1010
1010
1011
1011
1100
1100
1101
1101
1110
1110
1111
1111
Each additional bit doubles the number of possible combinations
Each additional bit doubles the number of possible combinations
14
Bit Combinations
Bit Combinations
Each combination can represent a particular item
Each combination can represent a particular item
There are 2
There are 2
N
N
combinations of N bits
combinations of N bits
Therefore, N bits are needed to represent 2
Therefore, N bits are needed to represent 2
N
N
unique items
unique items
2
2
1
1
= 2 items
= 2 items
2
2
2
2
= 4 items
= 4 items
2
2
3
3
= 8 items
= 8 items
2
2
4
4
= 16 items
= 16 items
2
2
5
5
= 32 items
= 32 items
1 bit ?
1 bit ?
2 bits ?
2 bits ?
3 bits ?
3 bits ?
4 bits ?
4 bits ?
5 bits ?
5 bits ?
How many
How many
items can be
items can be
represented by
represented by
15
A Computer Specification
A Computer Specification
Consider the following specification for a
Consider the following specification for a
personal computer:
personal computer:
•
600 MHz Pentium III Processor
600 MHz Pentium III Processor
•
256 MB RAM
256 MB RAM
•
16 GB Hard Disk
16 GB Hard Disk
•
24x speed CD ROM Drive
24x speed CD ROM Drive
•
17” Multimedia Video Display with 1280 x 1024
17” Multimedia Video Display with 1280 x 1024
resolution
resolution
•
56 KB Modem
56 KB Modem
What does it all mean?
What does it all mean?
16
Memory
Memory
Main memory is
Main memory is
divided into many
divided into many
memory locations
memory locations
(or
(or
cells
cells
)
)
9278
9278
9279
9279
9280
9280
9281
9281
9282
9282
9283
9283
9284
9284
9285
9285
9286
9286
Each memory cell
Each memory cell
has a numeric
has a numeric
address
address
, which
, which
uniquely identifies
uniquely identifies
it
it
17
Storing Information
Storing Information
9278
9278
9279
9279
9280
9280
9281
9281
9282
9282
9283
9283
9284
9284
9285
9285
9286
9286
Large values are
Large values are
stored in consecutive
stored in consecutive
memory locations
memory locations
10011010
10011010
Each memory cell
Each memory cell
stores a set number
stores a set number
of bits (usually 8
of bits (usually 8
bits, or one
bits, or one
byte
byte
)
)
18
Storage Capacity
Storage Capacity
Every memory device has a
Every memory device has a
storage capacity
storage capacity
,
,
indicating the number of bytes it can hold
indicating the number of bytes it can hold
Capacities are expressed in various units:
Capacities are expressed in various units:
KB
KB
2
2
10
10
= 1024
= 1024
MB
MB
2
2
20
20
(over 1 million)
(over 1 million)
GB
GB
2
2
30
30
(over 1 billion)
(over 1 billion)
TB
TB
2
2
40
40
(over 1 trillion)
(over 1 trillion)
Unit
Unit
Symbol
Symbol
Number of Bytes
Number of Bytes
kilobyte
kilobyte
megabyte
megabyte
gigabyte
gigabyte
terabyte
terabyte
19
Memory
Memory
Main memory is
Main memory is
volatile
volatile
- stored information
- stored information
is lost if the electric power is removed
is lost if the electric power is removed
Secondary memory devices are
Secondary memory devices are
nonvolatile
nonvolatile
Main memory and disks are
Main memory and disks are
direct access
direct access
devices - information can be reached directly
devices - information can be reached directly
The terms direct access and
The terms direct access and
random access
random access
are often used interchangeably
are often used interchangeably
A magnetic tape is a
A magnetic tape is a
sequential access
sequential access
device
device
since its data is arranged in a linear order -
since its data is arranged in a linear order -
you must get by the intervening data in order
you must get by the intervening data in order
to access other information
to access other information
20
RAM vs. ROM
RAM vs. ROM
RAM
RAM
- Random Access Memory (direct access)
- Random Access Memory (direct access)
ROM
ROM
- Read-Only Memory
- Read-Only Memory
The terms RAM and main memory are basically
The terms RAM and main memory are basically
interchangeable
interchangeable
ROM could be a set of memory chips, or a
ROM could be a set of memory chips, or a
separate device, such as a CD ROM
separate device, such as a CD ROM
Both RAM and ROM are random (direct) access
Both RAM and ROM are random (direct) access
devices!
devices!
RAM should probably be called Read-Write
RAM should probably be called Read-Write
Memory
Memory
21
The Central Processing Unit
The Central Processing Unit
A CPU is also called a
A CPU is also called a
microprocessor
microprocessor
It continuously follows the
It continuously follows the
fetch-decode-execute
fetch-decode-execute
cycle:
cycle:
fetch
Retrieve an instruction from main memory
Retrieve an instruction from main memory
decode
Determine what the
Determine what the
instruction is
instruction is
execute
Carry out the
Carry out the
instruction
instruction
22
The Central Processing Unit
The Central Processing Unit
(CPU)
(CPU)
The CPU contains:
The CPU contains:
Arithmetic / Logic Unit
Registers
Control Unit
Small
Small
storage
storage
areas
areas
Performs
Performs
calculations and
calculations and
decisions
decisions
Coordinates
Coordinates
processing
processing
steps
steps
23
The Central Processing Unit
The Central Processing Unit
The speed of a CPU is controlled by the
The speed of a CPU is controlled by the
system clock
system clock
The system clock generates an electronic
The system clock generates an electronic
pulse at regular intervals
pulse at regular intervals
The pulses coordinate the activities of the
The pulses coordinate the activities of the
CPU
CPU
The speed is measured in
The speed is measured in
megahertz
megahertz
(MHz)
(MHz)
24
Monitor
Monitor
The size of a monitor (17") is measured
The size of a monitor (17") is measured
diagonally, like a television screen
diagonally, like a television screen
Most monitors these days have
Most monitors these days have
multimedia
multimedia
capabilities: text, graphics, video, etc.
capabilities: text, graphics, video, etc.
A monitor has a certain maximum
A monitor has a certain maximum
resolution
resolution
,
,
indicating the number of picture elements,
indicating the number of picture elements,
called
called
pixels
pixels
, that it can display (such as 1280
, that it can display (such as 1280
by 1024)
by 1024)
High resolution (more pixels) produces
High resolution (more pixels) produces
sharper pictures
sharper pictures
25
Modem
Modem
Data transfer devices
Data transfer devices
allow information to be
allow information to be
sent and received between computers
sent and received between computers
Many computers include a
Many computers include a
modem
modem
, which
, which
allows information to be moved across a
allows information to be moved across a
telephone line
telephone line
A data transfer device has a maximum
A data transfer device has a maximum
data
data
transfer rate
transfer rate
A modem, for instance, may have a data
A modem, for instance, may have a data
transfer rate of 56,000
transfer rate of 56,000
bits per second
bits per second
(bps)
(bps)
26
Networks
Networks
A
A
network
network
is two or more computers that are
is two or more computers that are
connected so that data and resources can be
connected so that data and resources can be
shared
shared
Most computers are connected to some kind
Most computers are connected to some kind
of network
of network
Each computer has its own
Each computer has its own
network address
network address
,
,
which uniquely identifies it among the others
which uniquely identifies it among the others
A
A
file server
file server
is a network computer dedicated
is a network computer dedicated
to storing programs and data that are shared
to storing programs and data that are shared
among network users
among network users
27
Network Connections
Network Connections
Each computer in a network could be directly
Each computer in a network could be directly
connected to each other computer in the
connected to each other computer in the
network
network
These are called
These are called
point-to-point
point-to-point
connections
connections
This technique is not feasible for
This technique is not feasible for
more than a few close machines
more than a few close machines
Adding a computer requires
Adding a computer requires
a new communication line
a new communication line
for each computer already
for each computer already
in the network
in the network
28
Network Connections
Network Connections
Most modern networks share a single communication
Most modern networks share a single communication
line
line
Adding a new computer to the network is relatively easy
Adding a new computer to the network is relatively easy
Network traffic must take
Network traffic must take
turns using the line, which
turns using the line, which
introduces delays
introduces delays
Often information is broken
Often information is broken
down in parts, called
down in parts, called
packets
packets
,
,
which are sent to the receiving
which are sent to the receiving
machine then reassembled
machine then reassembled
29
Local-Area Networks
Local-Area Networks
LAN
LAN
A
A
Local-Area Network
Local-Area Network
(LAN) covers a small
(LAN) covers a small
distance and a small
distance and a small
number of computers
number of computers
A LAN often connects the machines
A LAN often connects the machines
in a single room or building
in a single room or building
30
Wide-Area Networks
Wide-Area Networks
LAN
LAN
A
A
Wide-Area Network
Wide-Area Network
(WAN)
(WAN)
connects two or more LANs,
connects two or more LANs,
often over long distances
often over long distances
A LAN is usually owned
A LAN is usually owned
by one organization, but
by one organization, but
a WAN often connects
a WAN often connects
different groups in
different groups in
different countries
different countries
LAN
LAN
31
The Internet
The Internet
The
The
Internet
Internet
is a WAN which spans the entire planet
is a WAN which spans the entire planet
The word Internet comes from the term
The word Internet comes from the term
internetworking
internetworking
, which implies communication
, which implies communication
among networks
among networks
It started as a United States government project,
It started as a United States government project,
sponsored by the Advanced Research Projects Agency
sponsored by the Advanced Research Projects Agency
(ARPA), and was originally called the ARPANET
(ARPA), and was originally called the ARPANET
The Internet grew quickly throughout the 1980s and
The Internet grew quickly throughout the 1980s and
90s
90s
Less than 600 computers were connected to the
Less than 600 computers were connected to the
Internet in 1983; now there are over 10 million
Internet in 1983; now there are over 10 million
32
TCP/IP
TCP/IP
A protocol is a set of rules that determine how things
A protocol is a set of rules that determine how things
communicate with each other
communicate with each other
The software which manages Internet communication
The software which manages Internet communication
follows a suite of protocols called
follows a suite of protocols called
TCP/IP
TCP/IP
The
The
Internet Protocol
Internet Protocol
(IP) determines the format of
(IP) determines the format of
the information as it is transferred
the information as it is transferred
The
The
Transmission Control Protocol
Transmission Control Protocol
(TCP) dictates
(TCP) dictates
how messages are reassembled and handles lost
how messages are reassembled and handles lost
information
information
33
IP and Internet Addresses
IP and Internet Addresses
Each computer on the Internet has a unique
Each computer on the Internet has a unique
IP
IP
address
address
, such as:
, such as:
204.192.116.2
204.192.116.2
Most computers also have a unique Internet name,
Most computers also have a unique Internet name,
which is also referred to as an
which is also referred to as an
Internet address
Internet address
:
:
renoir.villanova.edu
renoir.villanova.edu
kant.breakaway.com
kant.breakaway.com
The first part indicates a particular computer
The first part indicates a particular computer
(
(
renoir
renoir
)
)
The rest is the
The rest is the
domain name
domain name
, indicating the
, indicating the
organization (
organization (
villanova.edu
villanova.edu
)
)
34
Domain Names
Domain Names
The last section (the suffix) of each domain name
The last section (the suffix) of each domain name
usually indicates the type of organization:
usually indicates the type of organization:
edu
edu
com
com
org
org
net
net
- educational institution
- educational institution
- commercial business
- commercial business
- non-profit organization
- non-profit organization
- network-based organization
- network-based organization
Sometimes the suffix
Sometimes the suffix
indicates the country:
indicates the country:
New suffix categories
New suffix categories
are being considered
are being considered
uk
uk
au
au
ca
ca
se
se
- United Kingdom
- United Kingdom
- Australia
- Australia
- Canada
- Canada
- Sweden
- Sweden
35
Domain Names
Domain Names
A domain name can have several parts
A domain name can have several parts
Unique domain names mean that multiple
Unique domain names mean that multiple
sites can have individual computers with the
sites can have individual computers with the
same local name
same local name
When used, an Internet address is translated
When used, an Internet address is translated
to an IP address by software called the
to an IP address by software called the
Domain Name System
Domain Name System
(DNS)
(DNS)
There is
There is
no
no
one-to-one correspondence
one-to-one correspondence
between the sections of an IP address and the
between the sections of an IP address and the
sections of an Internet address
sections of an Internet address
36
The World-Wide Web
The World-Wide Web
The
The
World-Wide Web
World-Wide Web
allows many different types
allows many different types
of information to be accessed using a common
of information to be accessed using a common
interface
interface
A
A
browser
browser
is a program which accesses and
is a program which accesses and
presents information
presents information
•
text, graphics, sound, audio, video, executable programs
text, graphics, sound, audio, video, executable programs
A Web document usually contains
A Web document usually contains
links
links
to other
to other
Web documents, creating a
Web documents, creating a
hypermedia
hypermedia
environment
environment
The term Web comes from the fact that
The term Web comes from the fact that
information is not organized in a linear fashion
information is not organized in a linear fashion
37
The World-Wide Web
The World-Wide Web
Web documents are often defined using the
Web documents are often defined using the
HyperText Markup Language
HyperText Markup Language
(HTML)
(HTML)
Information on the Web is found using a
Information on the Web is found using a
Uniform Resource Locator
Uniform Resource Locator
(URL):
(URL):
http://www.lycos.com
http://www.lycos.com
http://www.villanova.edu/webinfo/domains.html
http://www.villanova.edu/webinfo/domains.html
ftp://java.sun.com/applets/animation.zip
ftp://java.sun.com/applets/animation.zip
A URL indicates a protocol (http), a domain,
A URL indicates a protocol (http), a domain,
and possibly specific documents
and possibly specific documents
38
Problem Solving
Problem Solving
The purpose of writing a program is to solve
The purpose of writing a program is to solve
a problem
a problem
The general steps in problem solving are:
The general steps in problem solving are:
•
Understand the problem
Understand the problem
•
Dissect the problem into manageable pieces
Dissect the problem into manageable pieces
•
Design a solution
Design a solution
•
Consider alternatives to the solution and refine it
Consider alternatives to the solution and refine it
•
Implement the solution
Implement the solution
•
Test the solution and fix any problems that exist
Test the solution and fix any problems that exist
39
Problem Solving
Problem Solving
Many software projects fail because the developer
Many software projects fail because the developer
didn't really understand the problem to be solved
didn't really understand the problem to be solved
We must avoid assumptions and clarify
We must avoid assumptions and clarify
ambiguities
ambiguities
As problems and their solutions become larger,
As problems and their solutions become larger,
we must organize our development into
we must organize our development into
manageable pieces
manageable pieces
This technique is fundamental to software
This technique is fundamental to software
development
development
We will dissect our solutions into pieces called
We will dissect our solutions into pieces called
classes and objects, taking an
classes and objects, taking an
object-oriented
object-oriented
approach
approach
40
The Java Programming
The Java Programming
Language
Language
A
A
programming language
programming language
specifies the words
specifies the words
and symbols that we can use to write a program
and symbols that we can use to write a program
A programming language employs a set of rules
A programming language employs a set of rules
that dictate how the words and symbols can be
that dictate how the words and symbols can be
put together to form valid
put together to form valid
program statements
program statements
Java was created by Sun Microsystems, Inc.
Java was created by Sun Microsystems, Inc.
It was introduced in 1995 and has become quite
It was introduced in 1995 and has become quite
popular
popular
It is an object-oriented language
It is an object-oriented language
41
Java Program Structure
Java Program Structure
In the Java programming language:
In the Java programming language:
•
A program is made up of one or more
A program is made up of one or more
classes
classes
•
A class contains one or more
A class contains one or more
methods
methods
•
A method contains program
A method contains program
statements
statements
These terms will be explored in detail
These terms will be explored in detail
throughout the course
throughout the course
A Java application always contains a method
A Java application always contains a method
called
called
main
main
See
See
Lincoln.java
Lincoln.java
(page 26)
(page 26)
42
Java Program Structure
Java Program Structure
public class MyProgram
{
}
// comments about the class
class header
class header
class body
class body
Comments can be added almost anywhere
Comments can be added almost anywhere
43
Java Program Structure
Java Program Structure
public class MyProgram
{
}
public static void main (String[] args)
{
}
// comments about the class
// comments about the method
method header
method header
method body
method body
44
Comments
Comments
Comments in a program are also called
Comments in a program are also called
inline
inline
documentation
documentation
They should be included to explain the purpose
They should be included to explain the purpose
of the program and describe processing steps
of the program and describe processing steps
They do not affect how a program works
They do not affect how a program works
Java comments can take two forms:
Java comments can take two forms:
// this comment runs to the end of the line
/* this comment runs to the terminating
symbol, even across line breaks */
45
Identifiers
Identifiers
Identifiers
Identifiers
are the words a programmer uses
are the words a programmer uses
in a program
in a program
An identifier can be made up of letters,
An identifier can be made up of letters,
digits, the underscore character (_), and the
digits, the underscore character (_), and the
dollar sign
dollar sign
They cannot begin with a digit
They cannot begin with a digit
Java is
Java is
case sensitive
case sensitive
, therefore
, therefore
Total
Total
and
and
total
total
are different identifiers
are different identifiers
46
Identifiers
Identifiers
Sometimes we choose identifiers ourselves when
Sometimes we choose identifiers ourselves when
writing a program (such as
writing a program (such as
Lincoln
Lincoln
)
)
Sometimes we are using another programmer's
Sometimes we are using another programmer's
code, so we use the identifiers that they chose
code, so we use the identifiers that they chose
(such as
(such as
println
println
)
)
Often we use special identifiers called
Often we use special identifiers called
reserved
reserved
words
words
that already have a predefined meaning in
that already have a predefined meaning in
the language
the language
A reserved word cannot be used in any other way
A reserved word cannot be used in any other way
47
Reserved Words
Reserved Words
The Java reserved words:
The Java reserved words:
abstract
boolean
break
byte
byvalue
case
cast
catch
char
class
const
continue
default
do
double
else
extends
false
final
finally
float
for
future
generic
goto
if
implements
import
inner
instanceof
int
interface
long
native
new
null
operator
outer
package
private
protected
public
rest
return
short
static
super
switch
synchronized
this
throw
throws
transient
true
try
var
void
volatile
while
48
White Space
White Space
Spaces, blank lines, and tabs are collectively
Spaces, blank lines, and tabs are collectively
called
called
white space
white space
White space is used to separate words and
White space is used to separate words and
symbols in a program
symbols in a program
Extra white space is ignored
Extra white space is ignored
A valid Java program can be formatted many
A valid Java program can be formatted many
different ways
different ways
Programs should be formatted to enhance
Programs should be formatted to enhance
readability, using consistent indentation
readability, using consistent indentation
See
See
Lincoln2.java
Lincoln2.java
and
and
Lincoln3.java
Lincoln3.java
49
Programming Language Levels
Programming Language Levels
There are four programming language
There are four programming language
levels:
levels:
•
machine language
machine language
•
assembly language
assembly language
•
high-level language
high-level language
•
fourth-generation language
fourth-generation language
Each type of CPU has its own specific
Each type of CPU has its own specific
machine language
machine language
The other levels were created to make it
The other levels were created to make it
easier for a human being to write programs
easier for a human being to write programs
50
Programming Languages
Programming Languages
A program must be translated into machine
A program must be translated into machine
language before it can be executed on a
language before it can be executed on a
particular type of CPU
particular type of CPU
This can be accomplished in several ways
This can be accomplished in several ways
A
A
compiler
compiler
is a software tool which translates
is a software tool which translates
source code
source code
into a specific target language
into a specific target language
Often, that target language is the machine
Often, that target language is the machine
language for a particular CPU type
language for a particular CPU type
The Java approach is somewhat different
The Java approach is somewhat different
51
Java Translation and Execution
Java Translation and Execution
The Java compiler translates Java source code
The Java compiler translates Java source code
into a special representation called
into a special representation called
bytecode
bytecode
Java bytecode is not the machine language for
Java bytecode is not the machine language for
any traditional CPU
any traditional CPU
Another software tool, called an
Another software tool, called an
interpreter
interpreter
,
,
translates bytecode into machine language and
translates bytecode into machine language and
executes it
executes it
Therefore the Java compiler is not tied to any
Therefore the Java compiler is not tied to any
particular machine
particular machine
Java is considered to be
Java is considered to be
architecture-neutral
architecture-neutral
52
Java Translation and Execution
Java Translation and Execution
Java source
code
Machine
code
Java
bytecode
Java
interpreter
Bytecode
compiler
Java
compiler
53
Development Environments
Development Environments
There are many development environments
There are many development environments
which develop Java software:
which develop Java software:
•
Sun Java Software Development Kit (SDK)
Sun Java Software Development Kit (SDK)
•
Borland JBuilder
Borland JBuilder
•
MetroWork CodeWarrior
MetroWork CodeWarrior
•
Microsoft Visual J++
Microsoft Visual J++
•
Symantec Café
Symantec Café
Though the details of these environments
Though the details of these environments
differ, the basic compilation and execution
differ, the basic compilation and execution
process is essentially the same
process is essentially the same
54
Syntax and Semantics
Syntax and Semantics
The
The
syntax rules
syntax rules
of a language define how we
of a language define how we
can put symbols, reserved words, and
can put symbols, reserved words, and
identifiers together to make a valid program
identifiers together to make a valid program
The
The
semantics
semantics
of a program statement define
of a program statement define
what that statement means (its purpose or
what that statement means (its purpose or
role in a program)
role in a program)
A program that is syntactically correct is not
A program that is syntactically correct is not
necessarily logically (semantically) correct
necessarily logically (semantically) correct
A program will always do what we tell it to
A program will always do what we tell it to
do, not what we
do, not what we
meant
meant
to tell it to do
to tell it to do
55
Errors
Errors
A program can have three types of errors
A program can have three types of errors
The compiler will find problems with syntax
The compiler will find problems with syntax
and other basic issues (
and other basic issues (
compile-time errors
compile-time errors
)
)
•
If compile-time errors exist, an executable version
If compile-time errors exist, an executable version
of the program is not created
of the program is not created
A problem can occur during program
A problem can occur during program
execution, such as trying to divide by zero,
execution, such as trying to divide by zero,
which causes a program to terminate
which causes a program to terminate
abnormally (
abnormally (
run-time errors
run-time errors
)
)
A program may run, but produce incorrect
A program may run, but produce incorrect
results (
results (
logical errors
logical errors
)
)
56
Introduction to Graphics
Introduction to Graphics
The last one or two sections of each chapter
The last one or two sections of each chapter
of the textbook focus on graphical issues
of the textbook focus on graphical issues
Most computer programs have graphical
Most computer programs have graphical
components
components
A picture or drawing must be digitized for
A picture or drawing must be digitized for
storage on a computer
storage on a computer
A picture is broken down into pixels, and
A picture is broken down into pixels, and
each pixel is stored separately
each pixel is stored separately
57
Representing Color
Representing Color
A black and white picture can be stored using
A black and white picture can be stored using
one bit per pixel (0 = white and 1 = black)
one bit per pixel (0 = white and 1 = black)
A color picture requires more information, and
A color picture requires more information, and
there are several techniques for representing a
there are several techniques for representing a
particular color
particular color
For example, every color can be represented as a
For example, every color can be represented as a
mixture of the three primary colors Red, Green,
mixture of the three primary colors Red, Green,
and Blue
and Blue
In Java, each color is represented by three
In Java, each color is represented by three
numbers between 0 and 255 that are collectively
numbers between 0 and 255 that are collectively
called an
called an
RGB value
RGB value
58
Coordinate Systems
Coordinate Systems
Each pixel can be identified using a two-
Each pixel can be identified using a two-
dimensional coordinate system
dimensional coordinate system
When referring to a pixel in a Java program,
When referring to a pixel in a Java program,
we use a coordinate system with the origin in
we use a coordinate system with the origin in
the upper left corner
the upper left corner
Y
X
(0, 0)
(112, 40)
112
40
Document Outline