A programming language specifies the words and symbols that we can use to write a program A programming language employs a set of rules that dictate how the words and symbols can be put together to form valid program statements The Java programming language was created by Sun Microsystems, Inc. It was introduced in 1995 and it's popularity has grown quickly since then.

1. Chapter 1
Introduction to Object-Oriented
Programming and Java
Faculty of Information Technology

2. Problem Solving
• The purpose of writing a program is to solve a
problem
• Solving a problem consists of multiple activities:
• Understand the problem
• Design a solution
• Consider alternatives and refine the solution
• Implement the solution
• Test the solution
• These activities are not purely linear – they overlap
and interact
1-2

3. Problem Solving
• The key to designing a solution is breaking it down
into manageable pieces
• When writing software, we design separate pieces
that are responsible for certain parts of the solution
• An object-oriented approach lends itself to this kind
of solution decomposition
• We will dissect our solutions into pieces called
objects and classes
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4. Object-Oriented
Programming• Java is an object-oriented programming language
• As the term implies, an object is a fundamental
entity in a Java program
• Objects can be used effectively to represent real-
world 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 1-4

5. Objects
• An object has:
• state - descriptive characteristics
• behaviors - what it can do (or what can be done to it)
• The state of a bank account includes its account
number and its current balance
• The behaviors associated with a bank account
include the ability to make deposits and
withdrawals
• Note that the behavior of an object might change
its state
1-5

6. Classes
• An object is defined by a class
• A class is the scheme of an object
• The class uses methods to define the behaviors of
the object
• The class that contains the main method of a Java
program represents the entire program
• A class represents a concept, and an object
represents the embodiment of that concept
• Multiple objects can be created from the same
class 1-6

7. Objects and Classes
1-7
Bank
Account
A class
(the concept)
John’s Bank Account
Balance: $5,257
An object
(the realization)
Bill’s Bank Account
Balance: $1,245,069
Mary’s Bank Account
Balance: $16,833
Multiple objects
from the same class

8. Java
• A programming language specifies the words and
symbols that we can use to write a program
• A programming language employs a set of rules
that dictate how the words and symbols can be put
together to form valid program statements
• The Java programming language was created by
Sun Microsystems, Inc.
• It was introduced in 1995 and it's popularity has
grown quickly since then.
1-8

9. Java, Web, and Beyond
• Java can be used to develop:
• Java Application
• Java Applet
• Java Web Applications
• Java can also be used to develop applications for
hand-held devices such as smart phones and cell
phones
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10. Examples of Java’s Versatility
(Applets)
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11. PDA and Cell Phone
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12. Language Levels
• There are three programming language levels:
• machine language
• assembly language
• high-level 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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13. Programming Languages
Machine Language
1-13
• 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.
• Program with native machine language is a tedious process.
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:
1101101010011010

14. Programming Languages
Assembly Language
1-14
• 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.
• For example, to add two numbers, you might write an
instruction in assembly code like this:
ADDF3 R1, R2, R3
…
ADDF3 R1, R2, R3
…
Assembly Source File
Assembler …
1101101010011010
…
Machine Code File

15. Programming Languages
High-Level Language
1-15
• The high-level languages are English-like and easy to learn
and program.
• For example, the following is a high-level language
statement that computes the area of a circle with radius 5:
area = 5 * 5 * 3.1415;

16. Programming Languages
• Each type of CPU executes only a particular machine
language
• A program must be translated into machine language
before it can be executed
• 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
1-16

17. 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 1-17

18. Java Translation
1-18
Java source
code
Machine
code
Java
bytecode
Bytecode
interpreter
Bytecode
compiler
Java
compiler

19. Java Virtual Machine
• 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.
1-19
Java Bytecode
Java Virtual
Machine
Any
Computer

20. Development Environments
• Two main component that support the
development of Java software:
• Sun Java Development Kit (JDK)
• Integrated Development Environment (IDE)
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21. JDK Versions
• 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 (possibly 2011) a. k. a. JDK 7 or Java 7
• JDK 8 or Java 7
• JDK 9 or Java 7 1-21

22. JDK Editions
• Java Standard Edition (J2SE)
• J2SE can be used to develop client-side standalone
applications or applets.
• Java Enterprise Edition (J2EE)
• J2EE can be used to develop server-side applications
such as Java servlets and Java ServerPages.
• Java Micro Edition (J2ME).
• J2ME can be used to develop applications for mobile
devices such as cell phones.
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23. Popular IDE
• Sun NetBeans
• IBM Eclipse
• Borland Jbuilder
• BlueJ
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24. A Simple Java Program
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
• File name: Welcome.java
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25. Creating and Editing Using NotePad
To use NotePad, type
notepad Welcome.java
from the DOS prompt.
1-25

26. Compiling and Running Java from the
Command Window
• Compile
• javac Welcome.java
• Run
• java Welcome
1-26

27. Compiling and Running Java from
NetBeans
• http://netbeans.org/kb/docs/java/quickstart.html
1-27

28. Creating, Compiling, and Running Programs
1-28
Source Code
Create/Modify Source Code
Compile Source Code
i.e., javac Welcome.java
Bytecode
Run Byteode
i.e., java Welcome
Result
If compilation errors
If runtime errors or incorrect result
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
…
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
Saved on the disk
stored on the disk
Source code (developed by the programmer)
Byte code (generated by the compiler for JVM
to read and interpret, not for you to understand)

29. Trace a Program Execution
1-29
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Enter main method

30. Trace a Program Execution
1-30
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Execute statement

31. Trace a Program Execution
1-31
//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

32. 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
• A Java application always contains a method called
main
1-32

33. Java Program Structure
1-33
public class MyProgram
{
}
// comments about the class
class header
class body
Comments can be placed almost anywhere

34. Java Program Structure
1-34
public class MyProgram
{
}
// comments about the class
public static void main (String[] args)
{
}
// comments about the method
method header
method body

35. 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 two forms:
1-35
// this comment runs to the end of the line
/* this comment runs to the terminating
symbol, even across line breaks */

36. 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
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37. Identifiers
• 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
1-37

38. Reserved Words
• The Java reserved words:
1-38
abstract
assert
boolean
break
byte
case
catch
char
class
const
continue
default
do
double
else
enum
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

39. White Space
• 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 many ways
• Programs should be formatted to enhance
readability, using consistent indentation
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40. 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
• The semantics of a program statement define what
that statement means (its purpose or role in a
program)
• 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 1-40

41. 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)
1-41

42. Basic Program Development
1-42
errors
errors
Edit and
save program
Compile program
Execute program and
evaluate results

43. Exercise 1.1
public class Exercise1_1 {
public static void main(String[] args) {
System.out.println("Welcome to Java");
System.out.println("Welcome to Computer Science");
System.out.println("Programming is fun");
}
}
1-43

44. Exercise 1.2
public class Exercise1_2 {
public static void main(String[] args) {
System.out.println("*");
System.out.println("**");
System.out.println("***");
System.out.println("****");
}
}
1-44

45. Try to solve this
1-45

46. Summary
• Chapter 1 focused on:
• components of a computer
• how those components interact
• how computers store and manipulate information
• programming and programming languages
• an introduction to Java
• an overview of object-oriented concepts
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