Download lecture1 - Lamar University

Programming Fundamentals I (COSC1336),
Lecture 1 (prepared after Chapter 1 of
Liang’s 2011 textbook)
Stefan Andrei
5/3/2017
COSC-1336, Lecture 1
1
Programming Fundamentals I
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COSC-1336-01 is a 3 credit points module:
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Assessments/Tutorials: 10%
Assignments: 25%
First Lesson exam: 5% (open book)
Mid-term exam: 20% (open book)
Written final exam: 40% (open book)
Lectures: 11:15am-12:05pm, room 107, on MWF
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New schedule: 11:05am-12:05pm – do you agree with this new
schedule?
Module homepage:
http://galaxy.lamar.edu/~sandrei/cosc-1336-01
5/3/2017
COSC-1336, Lecture 1
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Course Etiquette
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Code of conduct
no copying
 for details, see webpage
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You are encouraged to attend to all lectures,
tutorials, and so on.
You are encouraged to ask questions.
You are encouraged to offer answers.
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Contact Information and Textbooks
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Associate Professor:
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Lectures based on the book:
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Dr. Stefan Andrei, [email protected]
Office hours: 10:00am-11:00am, 1:30pm-2:30pm
on MWF, and anytime by email appointment
Liang: Introduction to Java programming: Eight
Edition, 2011 Pearson Education, 0132130807
Other recommended books:
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John Lewis, Peter DePasquale, and Joe Chase:
JAVA Foundations, Addison Wesley, 2008, ISBN:
0321429729
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COSC-1336, Lecture 1
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Overview of This Course
1. Introduction to Computers, Programs, and Java
(Chapter 1)
2. Elementary Programming (Chapter 2)
3. Selections (Chapter 3)
4. Loops (Chapter 4)
5. Methods (Chapter 5)
6. Arrays (Chapter 6)
7. Multidimensional Arrays (Chapter 7)
8. Objects and Classes (Chapter 8)
9. Strings and Text I/O (Chapter 9)
10. Thinking in Objects (Chapter 10)
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Course Objectives
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This is an introductory course for fundamental
concepts of programming in terms of JAVA.
Topics include introduction to the JAVA
programming language, data and expressions,
classes and objects, conditionals, loops and
arrays.
This course will work together with a laboratory
section COSC 1173.
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COSC-1336, Lecture 1
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Lecture Structure
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Reminder of last lecture
Overview
Content (new notions + examples)
Summary
Reading suggestions
Coming up next
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Few things about LU (instead of
reminder of last lecture)
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Lamar University, a member of The Texas State
University System, is accredited by the Commission on
Colleges of the Southern Association of Colleges and
Schools (SACS) to award associate, baccalaureate,
masters, and doctorate degrees (www.lamar.edu)
Computer Science Department, part of College of Arts
and Sciences, is accredited by Accreditation Board for
Engineering and Technology (ABET) (cs.lamar.edu)
LU ACM (Association of Computing Machinery)
acm.lamar.edu
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2008 Beaumont
Enterprise article
• The ACM Regional Programming
Contest (October 17-18, 2008).
• Programming language: Java or C++.
• The ‘Birds of Prey’ team: 19th out of 68.
• James Carnley
• Ricky Guidry
• Jacob Wallace
• The ‘Cardinals’ team: 55th out of 68.
• Ran Qi
• Suman Rajbhandari
• Vishal Patel
• Coach: Dr. Stefan Andrei.
• Join us to represent LU at this contest.
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COSC-1336, Lecture 1
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Lamar University in 2010
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1.
2.
According to the Local
Programming Contest,
we selected two teams:
‘The Exceptions’ team:
 Caleb Fenton,
 Zebulun Barnett,
 Yogesh Sangi.
‘Cardinals’ team:
 Ethan Hasson,
 Judson Ward,
 Rishi Dhanju.
5/3/2017
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Coach: Dr. Stefan Andrei.
Faculty Trainers:
 Dr. Stefan Andrei and
 Prof. Myers Foreman
Training sessions:
September and October
for 4-6 hours per week.
We selected one of the
best textbook for
programming contest
training [Skiena, 2008].
COSC-1336, Lecture 1
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The results were very good
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‘The Exceptions’ got 16th out of 71 teams
(solving 5 exercises out of 8).
‘Cardinals’ got 52nd (solving 3 exercises out
of 8).
‘The Exceptions’ team outperformed:
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5/3/2017
All teams competing at the LSU site.
Many teams from Oklahoma and Texas, including
all teams representing Texas Christian University,
Southern Methodist University and the University
of Houston.
COSC-1336, Lecture 1
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The
‘Top at Site’
Award
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Lamar University news
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COSC-1336, Lecture 1
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Computer Science is not only about …
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Word processors
Spreadsheets
Web browsers
Beaubouef, T., Mason, J.: Why the high attrition rate for
Computer Science students: some thoughts and observations.
In ACM SIGCSE Bulletin 37 (2), pp. 103-106, 2005
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Overview of This Lecture
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To review computer basics, programs, and operating
systems (§§1.2-1.4).
To explore the relationship between Java and the
World Wide Web (§1.5).
To distinguish the terms API, IDE, and JDK (§1.6).
To write a simple Java program (§1.7).
To display output on the console (§1.7).
To explain the basic syntax of a Java program
(§1.7).
To create, compile, and run Java programs (§1.8).
(GUI) To display output using the JOptionPane
output dialog boxes (§1.9).
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What is a Computer?
 A computer consists of a Central Processing Unit (CPU),
memory, hard disk, floppy disk, monitor, printer, and
communication devices.
Bus
Storage
Devices
e.g., Disk, CD,
and Tape
5/3/2017
Memory
CPU
Communication
Devices
Input
Devices
Output
Devices
e.g., Modem,
and NIC
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
COSC-1336, Lecture 1
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CPU
 The CPU is the “brain” of a computer. It retrieves
instructions from memory and executes them.
 The CPU speed is measured in megahertz (MHz), and 1
megahertz means 1 million pulses per second.
 The speed of the CPU has been improved continuously.
 If you buy a PC now, you can get an Intel Pentium 4
Processor at 3 gigahertz (1 gigahertz is 1000 megahertz).
Bus
Storage
Devices
e.g., Disk, CD,
and Tape
5/3/2017
Memory
CPU
Communication
Devices
Input
Devices
Output
Devices
e.g., Modem,
and NIC
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
COSC-1336, Lecture 1
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Memory
 The memory stores data and program instructions to
be send to CPU for execution.
 A memory unit is an ordered sequence of bytes, each
holds eight bits.
 A program and its data must be brought to memory
before they can be executed.
 The current content of a memory byte is lost whenever
new information is placed in it.
Bus
Storage
Devices
e.g., Disk, CD,
and Tape
5/3/2017
Memory
CPU
Communication
Devices
Input
Devices
Output
Devices
e.g., Modem,
and NIC
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
COSC-1336, Lecture 1
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How Data is Stored?
Data of various kinds, such as
numbers, characters, and
strings, are encoded as a series
of bits (zeros and ones).
 Computers use zeros and ones
because digital devices have two
stable states, which are referred
to as zero and one by
convention.
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Memory address
Memory content
.
.
.
.
.
.
2000
01001010
Encoding for character ‘J’
2001
01100001
Encoding for character ‘a’
2002
01110110
Encoding for character ‘v’
2003
01100001
Encoding for character ‘a’
2004
00000011
Encoding for number 3
The programmers need not to be concerned about the
encoding and decoding of data, which is performed
automatically by the system based on the encoding
scheme.
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How Data is Stored? (cont)
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The encoding scheme varies.
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Example: character ‘J’ is represented by 01001010
in one byte.
A small number such as 3 can be stored in a
single byte.
If computer needs to store a large number that
cannot fit into a single byte, it uses a number of
adjacent bytes.
No two data can share or split the same byte.
A byte is the minimum storage unit.
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Storage Devices
 Memory is volatile, because information is lost when the power is
off.
 Programs and data are permanently stored on storage devices
and are moved to memory when the computer actually uses them.
 There are three main types of storage devices:
 Disk drives (hard disks and floppy disks),
 CD drives (CD-R and CD-RW), and
 Tape drives.
Bus
Storage
Devices
e.g., Disk, CD,
and Tape
5/3/2017
Memory
CPU
Communication
Devices
Input
Devices
Output
Devices
e.g., Modem,
and NIC
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
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Output Devices: Monitor
 The monitor displays information (text and graphics).
 The resolution and dot pitch determine the quality of the
display.
Bus
Storage
Devices
e.g., Disk, CD,
and Tape
5/3/2017
Memory
CPU
Communication
Devices
Input
Devices
Output
Devices
e.g., Modem,
and NIC
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
COSC-1336, Lecture 1
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Monitor Resolution
resolution The resolution specifies the number of pixels per
square inch.
Pixels (short for “picture elements”) are tiny dots
that form an image on the screen.
The resolution can be set manually.
The higher the resolution, the sharper and clearer
the image is.
However, the image may be very small if you set
high resolution on a small screen monitor.
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Monitor Resolution and Dot Pitch
resolution PC monitors are usually 15-inch, 17-inch, 19-inch,
or 21-inch.
For a 15-inch monitor, a comfortable resolution
setting would be 640480 (307,200 pixels).
dot pitch The dot pitch is the amount of space between
pixels. The smaller the dot pitch, the better the
display.
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Communication Devices
 A regular modem uses a phone line and can transfer data in
a speed up to 56,000 bps (bits per second).
 A DSL (digital subscriber line) also uses a phone line and
can transfer data in a speed 20 times faster than a regular
modem.
 A cable modem uses the TV cable line maintained by the
cable company.
 A cable modem is as fast as a DSL.
Bus
Storage
Devices
e.g., Disk, CD,
and Tape
5/3/2017
Memory
CPU
Communication
Devices
Input
Devices
Output
Devices
e.g., Modem,
and NIC
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
COSC-1336, Lecture 1
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Communication Devices
 A Network Interface Card (NIC) is a device to connect a
computer to a Local Area Network (LAN).
 The LAN is commonly used in business, universities,
and government organizations.
 A typical type of NIC, called 10BaseT, can transfer data
at 10 mbps (million bits per second).
Bus
Storage
Devices
e.g., Disk, CD,
and Tape
5/3/2017
Memory
CPU
Communication
Devices
Input
Devices
Output
Devices
e.g., Modem,
and NIC
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
COSC-1336, Lecture 1
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Input Devices
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An input device is any peripheral (piece of
computer hardware equipment) used to provide
data and control signals to a computer.
Examples (traditional devices):
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Keyboard, Mouse, Scanner.
Examples (pointing devices, that is, any human
interface device that allows a user to input
spatial data to a computer):
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5/3/2017
Touch-screen, 3D mouse, Joystick, and so on.
COSC-1336, Lecture 1
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Programs
 Computer programs, known as software, are
instructions to the computer.
 You tell a computer what to do through programs.
 Without programs, a computer is an empty
machine.
 Computers do not understand human languages,
so you need to use computer languages to
communicate with them.
 Programs are written using programming
languages.
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Programming Languages
Machine Language
Assembly Language
High-Level Language
 Machine language is a set of primitive
instructions built into every computer.
 The instructions are in the form of binary code,
so you have to enter binary codes for various
instructions.
 Programming with native machine language is
a tedious process.
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Example: Machine language
 Moreover the programs are highly difficult to
read and modify.
 For example, to add two numbers, you might
write an instruction in binary like this:
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5/3/2017
1101101010011010
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Programming Languages
Machine Language
Assembly Language
High-Level Language
 Assembly languages were developed to make
programming easy.
 Since the computer cannot understand
assembly language, however, a program called
assembler is used to convert assembly language
programs into machine code.
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Example: assembly language
 For example, to add two numbers, you might
write an instruction in assembly code like this:

ADDF3 R1, R2, R3
Assembly Source File
…
ADDF3 R1, R2, R3
…
5/3/2017
Machine Code File
Assembler
COSC-1336, Lecture 1
…
1101101010011010
…
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Programming Languages
Machine Language
Assembly Language
High-Level Language
 The high-level languages are English-like and easy
to learn and program.
 Example 1: x = y + z;
 Example 2: the following is a high-level language
statement that computes the (approximate) area of a
circle with radius 5:

area = 5 * 5 * 3.1415;
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Popular High-Level Languages
COBOL (COmmon Business Oriented Language)
 FORTRAN (FORmula TRANslation)
 BASIC (Beginner All-purpose Symbolic Instructional Code)
 Pascal (named for Blaise Pascal)
 Ada (named for Ada Lovelace)
 C (whose developer designed B first)
 Visual Basic (Basic-like visual language developed by
Microsoft)
 Delphi (Pascal-like visual language developed by Borland)
 C++ (an object-oriented language, based on C)
 C# (a Java-like language developed by Microsoft)
 Java (We use it in these lectures)
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Compiling Source Code
 A program written in a high-level language is called
a source program (a.k.a., source file or source code).
 Since a computer cannot understand a source
program, a program called a compiler is used to
translate the source program into a machine
language program called an object program.
Source File
Compiler
Machine-language
File
Linker
Executable File
Library Code
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Compiling Source Code (cont.)
 The object program is often then linked with other
supporting library code before the object can be
executed on the machine.
Source File
Compiler
Machine-language
File
Linker
Executable File
Library Code
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Operating Systems
The Operating System
(OS) is a program that
manages and controls a
computer’s activities.
The most common
operating system is
Windows.
 Here are some recent
versions: Windows 95, 98,
NT, 2000, XP, 7.
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COSC-1336, Lecture 1
User
Application Programs
Operating System
Hardware
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Operating Systems (cont.)
 Windows is currently the
most popular PC operating
system.
 Application programs
such as an Internet
browser and a word
processor cannot run
without an operating
system.
5/3/2017
COSC-1336, Lecture 1
User
Application Programs
Operating System
Hardware
38
Why Java?
 The answer is that Java enables users to develop
and deploy applications on the Internet for servers,
desktop computers, and small hand-held devices.
 Java is a general purpose programming language.
 The future of computing is being profoundly
influenced by the Internet, and Java promises to
remain a big part of that future.
 Java is the Internet programming language.
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39
Java, Web, and Beyond
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Java can be used to develop client-server
Web applications, such as Java Applets and
Java Servlets.
Java can also be used to develop applications
for hand-held devices such as Palm and cell
phones.
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COSC-1336, Lecture 1
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Examples of Java’s Versatility (Applets)
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COSC-1336, Lecture 1
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PDA
and Cell Phone
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Java’s History
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James Gosling and Sun Microsystems
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Oak
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Java, May 20, 1995, Sun World
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HotJava was the first browser to support Java
applets, and was Sun's demonstration platform
for the then new technology.
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Early History Website:
http://java.sun.com/features/1998/05/birthday.html
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Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Architecture-Neutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
www.cs.armstrong.edu/liang/intro8e/JavaCharacteristics.pdf
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Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
5/3/2017
Java is partially modeled on C++, but
greatly simplified and improved. Some
people refer to Java as "C++--" because it
is like C++ but with more functionality and
fewer negative aspects.
COSC-1336, Lecture 1
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Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
5/3/2017
Java is inherently object-oriented.
Although many object-oriented
languages began strictly as procedural
languages, Java was designed from
the start to be object-oriented. Objectoriented programming (OOP) is a
popular programming approach that is
replacing traditional procedural
programming techniques.
One of the central issues in software
development is how to reuse code.
Object-oriented programming provides
great flexibility, modularity, clarity, and
reusability through encapsulation,
inheritance, and polymorphism.
COSC-1336, Lecture 1
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Object-Oriented Programming
Java is an object-oriented programming
language.
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As the term implies, an object is a fundamental
entity in a Java program.
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Objects can be used effectively to represent realworld entities.

For instance, an object might represent a
particular employee in a company.

Each employee object handles the processing
and data management related to that employee.

5/3/2017
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Difference between traditional and
object-oriented approaches
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The conventional approach tends to consider
data and behavior separate.
The object-oriented approach considers data
and behavior together in a concept called class.
Example:

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5/3/2017
Conventional approach: 1 large room with scanners
and printers.
Object-oriented approach: 2 smaller rooms, one with
scanners and the other one with printers.
COSC-1336, Lecture 1
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Difference between traditional and
object-oriented approaches (cont)

Another example: suppose you have a fruit
basket with apples, peaches, and pineapples,
and two knives to peal off these fruits:
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5/3/2017
Conventional approach: one large basket with all fruits
and one drawer with two knives.
Object-oriented approach: three smaller baskets, one
with apples and their knife, another with peaches with
no knife, and the last one with pineapples and the
larger knife.
COSC-1336, Lecture 1
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Traditional approach → Java
public class FruitBasket {
static String nameOfFruit = "";
static int typeKnife = 0;
public static void main(String args[]) {
nameOfFruit = "apple";
typeKnife = 1;
System.out.println("We eat " + nameOfFruit +
" with " + typeKnife);
nameOfFruit = "Pineapple";
typeKnife = 2;
System.out.println("We eat " + nameOfFruit +
" with " + typeKnife);
// ... The operations ...
}
}
5/3/2017
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Object-oriented approach → Java
class Fruit {
String nameOfFruit;
int typeKnife;
Fruit(String nF, int tK) {
nameOfFruit = nF; typeKnife = tK;
}
// ... The operations ...
}
public class FruitBasket {
public static void main(String args[]) {
Fruit obj1 = new Fruit("apple", 1);
System.out.println("We eat " + obj1);
Fruit obj2 = new Fruit("pineapple", 2);
System.out.println("We eat " + obj2);
}
}
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Difference between traditional and
object-oriented approaches (cont)

Another example: manual gear versus
automatic gear vehicle:
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5/3/2017
Conventional approach: manual gear, hence
the responsibility of changing the gear belongs
to the driver.
Object-oriented approach: automatic gear,
hence the operation of changing the gear while
driving is embedded into the car specification.
The driver does not need to change any gear!
COSC-1336, Lecture 1
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Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
5/3/2017
Distributed computing involves several
computers working together on a
network.
Java is designed to make distributed
computing easy.
Since networking capability is
inherently integrated into Java, writing
network programs is like sending and
receiving data to and from a file.
COSC-1336, Lecture 1
53
Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
5/3/2017
You need an interpreter to run Java
programs.
The programs are compiled into the
Java Virtual Machine (JVM) code
called bytecode.
The bytecode is machine-independent
and can run on any machine that has a
Java interpreter, which is part of the
Java Virtual Machine.
COSC-1336, Lecture 1
54
Characteristics of Java
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




Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
5/3/2017
Java compilers can detect many
problems that would first show up at
execution time in other languages.
Java has eliminated certain types of
error-prone programming constructs
found in other languages.
Java has a runtime exception-handling
feature to provide programming
support for robustness.
COSC-1336, Lecture 1
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Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
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Java implements several security
mechanisms to protect your system
against harm caused by stray
programs.
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Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
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Write once, run anywhere
With a Java Virtual Machine (JVM),
you can write one program that will
run on any platform.
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Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
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Because Java is architecture neutral,
Java programs are portable.
They can be run on any platform
without being recompiled.
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Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
5/3/2017
Java’s performance is sometimes criticized.
The execution of the byte-code is never as
fast as it would be with a compiled language,
such as C++. Because Java is interpreted,
the byte-code is not directly executed by the
system, but is run through the interpreter.
The new JVM uses the technology known as
just-in-time compilation. It compiles
byte-code into native machine code, stores
the native code, and re-invokes the native
code when its bytecode is executed. Sun
recently developed the Java HotSpot
Performance Engine, which includes a
compiler for optimizing the frequently used
code. The HotSpot Performance Engine can
be plugged into a JVM to dramatically boost
its performance.
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Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Multithread programming is smoothly
integrated in Java, whereas in other
Java's Performance
languages you have to call procedures
Java Is Multithreaded specific to the operating system to enable
multithreading.
Java Is Dynamic
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Characteristics of Java
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Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureJava was designed to adapt to an evolving
Neutral
environment. New code can be loaded on
Java Is Portable
the fly without recompilation. There is no
need for developers to create, and for users
Java's Performance
to install, major new software versions.
Java Is Multithreaded New features can be incorporated
transparently as needed.
Java Is Dynamic
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JDK Versions
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JDK 1.02 (1995)
JDK 1.1 (1996)
JDK 1.2 (1998)
JDK 1.3 (2000)
JDK 1.4 (2002)
JDK 1.5 (2004) a. k. a. JDK 5 or Java 5
JDK 1.6 (2006) a. k. a. JDK 6 or Java 6
JDK 1.7 (2010) a. k. a. JDK 7 or Java 7
Sun Microsystems merged Oracle (April 2010) –
hence Java can be found at
www.oracle.com/technetwork/java/index.html
instead of java.sun.com
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JDK Editions
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Java Standard Edition (J2SE)
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Java Enterprise Edition (J2EE)
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J2EE can be used to develop server-side applications
such as Java servlets and Java ServerPages.
Java Micro Edition (J2ME).

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J2SE can be used to develop client-side standalone
applications or applets.
J2ME can be used to develop applications for mobile
devices such as cell phones.
Liang’s book uses J2SE to introduce Java
programming.
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Popular Java Integrated Development
Environments (IDEs)

NetBeans: Open Source by Sun
(http://netbeans.org/)

Eclipse: Open Source by IBM
(http://www.eclipse.org/platform/)
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A Simple Java Program
Listing 1.1
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
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Creating and Editing Using NotePad
To use NotePad, type
notepad Welcome.java
from the DOS prompt.
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Creating and Editing Using WordPad
To use WordPad, type
write Welcome.java
from the DOS prompt.
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Creating, Compiling, and Running
Programs
Create/Modify Source Code
Source code (developed by the programmer)
Saved on the disk
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Byte code (generated by the compiler for JVM
to read and interpret, not for you to understand)
…
Method Welcome()
0 aload_0
…
Method void main(java.lang.String[])
0 getstatic #2 …
3 ldc #3 <String "Welcome to
Java!">
5 invokevirtual #4 …
8 return
Source Code
Compile Source Code
i.e., javac Welcome.java
If compilation errors
stored on the disk
Bytecode
Run Byteode
i.e., java Welcome
Result
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If runtime errors or incorrect result
68
Compiling Java Source Code
 You can port a source
program to any machine with
appropriate compilers.
 The source program must be
recompiled (if you didn’t send
the bytecode program, too),
however, because the object
program can only run on a
specific machine.
 Nowadays computers are
networked to work together.
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Java Bytecode
Java Virtual
Machine
Any
Computer
69
Compiling Java Source Code
 Java was designed to run object
programs on any platform.
 With Java, you write the program
once, and compile the source
program into a special type of
object code, known as bytecode.
 The bytecode can then run on
any computer with a Java Virtual
Machine, as shown below.
 Java Virtual Machine is a
software that interprets Java
bytecode.
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Java Bytecode
Java Virtual
Machine
Any
Computer
70
Trace a Program Execution
Enter main() method
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
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Trace a Program Execution
Execute statement
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
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Trace a Program Execution
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
print a message to the
console
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Supplements on the Companion Website
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See Supplement I.B for installing and
configuring JDK.
See Supplement I.C for compiling and running
Java from the command window for details.
www.cs.armstrong.edu/liang/intro8e
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Review Question Answers
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Compiling and Running Java from the
Command Window
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Set path to JDK bin directory
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Set classpath to include the current directory
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set classpath=.
Compile
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set path=c:\Program Files\java\jdk1.6.0\bin
javac Welcome.java
Run
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java Welcome
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Compiling and Running Java from
TextPad
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See Supplement II.A on the Website for
details.
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Anatomy of a Java Program
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Comments
Reserved words
Modifiers
Statements
Blocks
Classes
Methods
The main() method
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Comments
 Three types of comments in Java:
1. Line comment: A line comment is preceded by two
slashes (//) in a line.
2. Paragraph comment: A paragraph comment is
enclosed between /* and */ in one or multiple lines.
3. javadoc comment: javadoc comments begin with
/** and end with */.
 They are used for documenting classes, data, and
methods.
 They can be extracted into an HTML file using JDK's
javadoc command.
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Reserved Words
 Reserved words (a.k.a., keywords) are words
that have a specific meaning to the compiler and
cannot be used for other purposes in the
program.
 For example, when the compiler sees the word
class, it understands that the word after class is
the name for the class.
 Other reserved words in Listing 1.1 are public,
static, and void.
 Their use will be introduced later in the lessons.
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Modifiers
 Java uses certain reserved words called modifiers that
specify the properties of the data, methods, and classes
and how they can be used.
 Examples of modifiers:
 public, static, private, final, abstract, protected,
and so on.
 A public datum, method, or class can be accessed by
other programs.
 A private datum or method cannot be accessed by
other programs.
 Modifiers are discussed in Chapter 6, “Objects and
Classes.”
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Statements
 In Java, a direct instruction that tells the computer
to do something is called a statement.
 A statement represents an action or a sequence of
actions.
 The statement
System.out.println("Welcome to Java!");
 in the program in Listing 1.1 is a statement to
display the greeting "Welcome to Java!"
 Every statement in Java ends with a semicolon (;).
 In addition, the above statement is a method call, too.
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Blocks
 A pair of braces in a program forms a block that
groups components of a program.
public class Test {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
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Method block
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Classes
 The class is the most essential Java construct.
 A class is a template or blueprint for objects.
 To program in Java, you must understand
classes and be able to write and use them.
 The mystery of the class will continue to be
unveiled throughout the lessons.
 For now, though, understand that a program is
defined by using one or more classes.
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Methods
 What is System.out.println()?
 It is a method call:
a collection of statements that performs a sequence of operations
to display a message on the console.
 It can be used even without fully understanding the details
of how it works.
 It is used by invoking a statement with a string argument.
 The string argument is enclosed within parentheses.
 In this case, the argument is "Welcome to Java!"
 You can call the same println() method with a different
argument to print a different message.
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The main() method
 The main() method provides the control of
program flow.
 The Java interpreter executes the application by
invoking the main() method.
 The main() method looks like this:
public static void main(String[] args) {
// Statements;
}
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Displaying Text in a Message Dialog Box
 You can use the showMessageDialog() method
in the JOptionPane class.
 JOptionPane is one of the many predefined
classes in the Java system, which can be reused
rather than “reinventing the wheel.”
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WelcomeInMessageDialogBox.java
/** This application program displays Welcome to Java!
* in a message dialog box.
*/
import javax.swing.JOptionPane;
public class WelcomeInMessageDialogBox {
public static void main(String[] args) {
// Display Welcome to Java! in a message dialog box
JOptionPane.showMessageDialog(null, "Welcome to Java!");
}
}

http://blogs.oracle.com/thejavatutorials/entry/why_is_swing_called_swing
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Compiling and Running the program
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The showMessageDialog() Method
JOptionPane.showMessageDialog(null,
"Welcome to Java!",
"Display Message",
JOptionPane.INFORMATION_MESSAGE);
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Two Ways to Invoke the Method
There are several ways (at least two) to use the
showMessageDialog() method:
1. One is to use a statement as shown in the example:

JOptionPane.showMessageDialog(null, x,
y, JOptionPane.INFORMATION_MESSAGE);
where x is a String for the text to be displayed, and y
is a String for the title of the message dialog box.
2. The other is to use a statement like this:

JOptionPane.showMessageDialog(null, x);

where x is a String for the text to be displayed.
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A general Java class syntax
//
comments about the class
public class MyProgram {
class header
class body
}
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Comments can be placed almost anywhere
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The main() method syntax (test driver)
//
comments about the class
public class MyProgram {
// comments about the method
public static void main (String[] args) {
method body
method header
}
}
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Summary
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To review computer basics, programs, and operating
systems (§§1.2-1.4).
To explore the relationship between Java and the
World Wide Web (§1.5).
To distinguish the terms API, IDE, and JDK (§1.6).
To write a simple Java program (§1.7).
To display output on the console (§1.7).
To explain the basic syntax of a Java program
(§1.7).
To create, compile, and run Java programs (§1.8).
(GUI) To display output using the JOptionPane
output dialog boxes (§1.9).
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Reading suggestions

From [Liang: Introduction to Java programming:
Eight Edition, 2011 Pearson Education,
0132130807]
 Chapter 1 (Introduction)
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Coming up next

From [Liang: Introduction to Java
programming: Eight Edition, 2011 Pearson
Education, 0132130807]

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Chapter 2 (Elementary Programming)
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Thank you for your attention!
Questions?
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