oop chapter 1 by jlncrnl
TRANSCRIPT
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Chapter 1Introduction
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Outline
Brief History of Java
The Java Programming Language
Program Development
Object-Oriented Programming
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Brief History of java
In 1990, Sun Microsystems began an internal project known as
the Green Projectto work on a new technology.
In 1992, the Green Project was spun off and its interest directedtoward building highly interactive devices for the cable TV
industry. This failed to materialize.
In 1994, the focus of the original team was re-targeted, this tim
to the use of Internet technology. A small web browser calledHotJavawas written. Oak was renamed toJavaafter learning
that Oak had already been trademarked.
In 1995, Java was first publicly released.
In 1996, Java Development Kit (JDK) 1.0 was released.
In 2002, JDK 1.4 (codenameMerlin) was released, the most
widely used version.
In 2004, JDK 5.0 (codename Tiger) was released, the latest
version.
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James Gosling
James Goslingis generally
credited as the inventor of the Java
programming language
He was the first designer of Java
and implemented its original
compiler and virtual machine He is also known as the Father of
Java
He is currently the Chief Technical
Officer of Sun Microsystems
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Java
A programm ing languagespecifies the words andsymbols 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 prog ram statements
The Java programming language was created by
Sun Microsystems, Inc.
It was introduced in 1995 and it's popularity hasgrown quickly since
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Java Platform Editions
A Java Platform is the set of APIs, class libraries, and other programs
used in developing Java programs for specific applications
There are 3 Java Platform Editions
1. Java SE (Standard Edition)- formerly J2SE
Core Java Platform targeting applications running on workstations
2. Java EE (Enterprise Edition) formerly J2EE
Component-based approach to developing distributed, multi-tier
enterprise applications
3. Java ME (Mobile Edition), formerly J2ME
Targeted at small, stand-alone or connectable consumer and
embedded devices
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Java Development Kit (JDK)
Java Development Kit (JDK)
Is a set of Java tools for developing Java programs
Consists of Java API, Java Compiler, and JVM
Java Application Programming Interface (API)
Is prewritten code, organized into packages of similar topics
Java Virtual MachineJava API
MyProgram.java
Hardware - Based Platform
JDK
JRE
Java VirtualMachine (JVM)
Is an
execution engine that
runs compiled Java
byte code
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Java Program Structure
In the Java programming language: A programis made up of one or more classes
A classcontains one or more methods
A methodcontains program statements
A Java application always contains a methodcalledmain
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Java Program Structure
public classMyProgram
{
}
// comments about the class
class header
class body
Comments can be placed almost anywhere
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Java Program Structure
public class MyProgram
{
}
// comments about the class
public static voidmain(String[] args)
{
}
// comments about the method
method header
method body
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The First Java Program
classWelcome{
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public static void main (String [ ] args) {
System.out.println("Welcome to Java!");
}
}
Type all carefully and save it to a
file named Welcome.java
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The First Java Program
classWelcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public static void main (String [ ] args) {
System.out.println("Welcome to Java!");
}
}
Java program source files (.java)
contain definition of classes
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The First Java Program
class Welcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public static voidmain(String [ ] args) {
System.out.println("Welcome to Java!");
}
}
Curly braces pair enclose a block
of code, method main()here
Dont miss me!
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The First Java Program
class Welcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public static void main (String [ ] args) {
System.out.println("Welcome to Java!");
}
}
This is a block of comments, for
human, not for computer
It explains to you what happens
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The First Java Program
class Welcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public static void main (String [ ] args) {
System.out.println("Welcome to Java!");
}
}
This is a method of the class
Welcome, named main()
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The First Java Program
class Welcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public static void main (String [ ] args){
System.out.println("Welcome to Java!");
}
}
There MUSTbe a pair of
parentheses following ALL
method names
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The First Java Program
class Welcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public static void main (String [ ] args) {
System.out.println("Welcome to Java!");
}
}
A method maytake some input
from the caller, formally known as
argumentsorparameters
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The First Java Program
class Welcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public static voidmain (String [ ] args) {
System.out.println("Welcome to Java!");
}
}
A method maygive some output to the
caller too, known as return value
void means no return value
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The First Java Program
class Welcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public staticvoid main (String [ ] args) {
System.out.println("Welcome to Java!");
}
}
The statickeyword before a
method definition indicates this is
a class method
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The First Java Program
class Welcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
publicstatic void main (String [ ] args) {
System.out.println("Welcome to Java!");
}
}
This method is apublicone, others
can callme.
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The First Java Program
class Welcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public static void main(String [ ] args) {
System.out.println("Welcome to Java!");
}
}
Standard properties of the main() method
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The First Java Program
class Welcome {
/* The Welcome Program-------------------
Illustrates a simple program displaying
a message.
*/
public static void main (String [ ] args) {
System.out.println("Welcome to Java!");
}
}
A statement(instruction) to display
a message
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The First Java Program
Change to the directory containing the fileWelcome.java
Typejavac Welcome.java
It generates a new fileWelcome.class
Type (without .class)
java Welcome
Whats the result?
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Comments
Comments in a program are called in l ine
documentat ion
They should be included to explain the purposeof 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 terminatingsymbol, even across line breaks */
/** this is a javadoccomment */
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Identifiers
Identi f iersare the words a programmer uses in aprogram
An identifier can be made up of letters, digits, theunderscore character ( _ ), and the dollar sign
Identifiers cannot begin with a digit Java is case sens it ive-Total, total, andTOTAL are different identifiers
By convention, programmers use different case
styles for different types of identifiers, such as t i t le casefor class names - Lincoln
upper casefor constants -MAXIMUM
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Identifiers
Sometimes we choose identifiers ourselves whenwriting a program (such as Lincoln)
Sometimes we are using another programmer's
code, so we use the identifiers that he or she
chose (such asprintln)
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
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Reserved Words
The Java reserved words:
abstract
assert
boolean
break
bytecase
catch
char
class
const
continuedefault
do
double
else
enum
extends
false
finalfinally
float
for
goto
if
implementsimport
instanceof
int
interface
long
native
new
nullpackage
private
protected
public
return
shortstatic
strictfp
super
switch
synchronized
this
throw
throwstransient
true
try
void
volatile
while
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White Space
Spaces, blank lines, and tabs are called white
space
White spaceis 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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Outline
The Java Programming Language
Program Development
Object-Oriented Programming
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Program Development
The mechanics of developing a program include
several activities
writing the program in a specific programming language
(such as Java)
translating the program into a form that the computer canexecute
investigating and fixing various types of errors that can
occur
Software tools can be used to help with all parts ofthis process
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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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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 compi leris a software tool which translates
source codeinto 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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Java Translation
The Java compiler translates Java source code
into a special representation called bytecode
Java bytecode is not the machine languagefor 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 anyparticular machine
Java is considered to be architecture-neutral
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Java Translation
Java sourcecode
Machinecode
Java
bytecode
Bytecode
interpreter
Bytecode
compiler
Java
compiler
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COREJAVA
Java source.java
javac
Java bytecode .class
JVM
Programming API
Platform interface
of Web Browse
JVM
Programming API
Platform interface
of Windows
JVM
Programming API
Platform interface
of Unix
java
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Development Environments
There are many programs that support the
development of Java software, including:
Sun Java Development Kit (JDK)
Sun NetBeans
IBM Eclipse
Borland JBuilder
MetroWerks CodeWarrior
BlueJ
jGRASP
Though the details of these environments differ,
the basic compilation and execution process is
essentially the same
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Syntax and Semantics
The syntaxru lesof a language define how we can
put together symbols, reserved words, and
identifiers to make a valid program
The semant icsof a program statement define what
that statement means (its purpose or role in aprogram)
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
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Errors
A program can have three types of errors
The compiler will find syntax errors and other
basic problems (compi le-t ime 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-t ime errors)
A program may run, but produce incorrect results,
perhaps using an incorrect formula (log icalerrors)
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Basic Program Development
errors
errors
Edit and
save program
Compile program
Execute program and
evaluate results
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Outline
Brief History of Java
The Java Programming Language
Program Development
Object-Oriented Programming
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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 linearthey
overlap and interact
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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 ob ject-or iented app roachlends itself to this
kind of solution decomposition
We will dissect our solutions into pieces calledobjects and classes
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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
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Objects
An object has:
state - descriptive characteristics (attributes)
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
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Classes
An object is defined by a class
A class is the blueprintof 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
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Objects and Classes
Bank
Account
A class
the concept)
Johns Bank Account
Balance: $5,257
An object
the realization)
Bills Bank AccountBalance: $1,245,069
Marys Bank AccountBalance: $16,833
Multiple objects
from the same class
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Lesson: Working with Classes
How to Create a New Class
How to Add Instance Data Members
How to Add Methods
How to Create an Instance of a Class
How to Use Constructors
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How to Create a New Class
Create a new class by using the Add Class
command on the Project menu
Example of new class named BankAccount:
public class BankAccount {
}
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How to Add Instance Data Members
Adding a data member named balance
public class BankAccount {
privatedoublebalance;
}
Keyword Definition
Public Accessible everywhere
Private Accessible only within the type itself
ProtectedAccessible only by classes which inheritfrom the class
H Add M h d
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How to Add Methods
Adding a method named Deposit
public class BankAccount {
privateDouble balance;
publicdouble Deposit (doubleamount) {balance += amount;
}
}
Overloaded methods: two or more methods withthe same name but different signatures
Example:MessageBox.Show
How to Create an Instance of a
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How to Create an Instance of a
Class Using the New keyword to create an instance of
the BankAccount class:
public class Bank {
public static void main (string args[]) {BankAccount account = newBankAccount( )
account.Deposit(500.00)
}
}
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P ti C ti Cl
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Practice: Creating a Class
In this practice, you will create aBankAccount class with methods
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How to Use Constructors
Executes code when object is instantiated
public class New {
public int New (inti) {value = i
}
}
Can overload, but does not use Overloads keyword
public class New {
public int New () {
value = 1 }
}
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What Is Inheritance?
Inheritance specifies an is-a-kind-of relationship
Multiple classes share the same attributes andoperations, allowing efficient code reuse
Examples:
A customer is a kind of person
An employee is a kind of person
Customer Employee
Person
Base Class
Derived Classes
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Inheritance
One class can be used to derive another via
inheri tance
Classes can be organized into hierarchies
BankAccount
Account
ChargeAccount
SavingsAccount
CheckingAccount
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How to Inherit from a Class
A derived class inherits from a base class
Properties, methods, data members, events, and
event handlers can be inherited (dependent on
scope)
Keywords
Inheritsinherits from a base class
NotInheritablecannot be inherited from
MustInheritinstances of the class cannot be created;
must be inherited from as a base class
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What Is Polymorphism?
The method name resides in the base class
The method implementations reside in the derived
classes
BaseTaxCalculateTax( )
CountyTax
CalculateTax( )
CityTax
CalculateTax( )
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C C S
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Comparing Classes to Structures
Classes Structures
Can define data members,
properties, and methods
Can define data members,properties, and methods
Support constructors and
member initialization
No default constructor or
member initialization
Support Finalizemethod Do not support Finalizemethod
Extensible by inheritance Do not support inheritance
Reference type Value type
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Key Points
A Java source file can include package, import
and class declarations in that order Themain()method is the start of execution of a
Java application
Each Java statement is terminated by a
semicolon ; Identifiers are case-sensitive
Java keywords cannot be used as identifiers
Each variable must be declared with a data type
There are 8 primitive data types:boolean, char,byte, short, int, long, floatand double
There are 3 reference data types: class, array and
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K P i t
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Key Points
if()and switch()are used for branching
statements
while(), do-while()and for()are used for
iterating statements
break, continueand labelare used to branch
inside loops
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S
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Summary
Chapter 1 focused on:
programming and programming languages
an introduction to Java
an overview of object-oriented concepts