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Matakuliah
Tahun
Versi
: T0053/Web Programming
: 2006
:2
Pertemuan 6
Object Oriented Programming
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Mengimplementasikan konsep OOP
dalam bahasa pemrograman Java
• Membuat program Java dengan konsep
OOP
2
Outline Materi
•
•
•
•
•
•
Introduction
Encapsulation
Inheritance
Polymorphism
Interface
Package
3
Procedural versus OOP
• Procedural programming language
– C is an example
– Action-oriented
– Functions are units of programming
• Object-oriented programming language
– Java is an example
– Object-oriented
– Classes are units of programming
• Functions, or methods, are encapsulated in
classes
4
OOP In Java
• Every java program implement all OOP
Concept:
– Encapsulation: all java program must reside in
class, no class, no program
– Inheritance: all class have a superclass, if not
mentioned, it’s automatically subclassing from
Object class
– Polymorphism: all method are polymorphic in
default
5
Encapsulation
• “Packaging an object’s variables within
protective custody of its methods”
• Advantages:
– Modularity
– Information Hiding: object has a public
interface for communicate to others, so it can
maintain private information and method that
can be changed any time without affecting the
communication
• Java Keyword: class
6
OOP Concept: Object
• Real world objects share 2 characteristics:
– State
• Dogs have state: name, color, breed, hungry
• Bicycles have state: current gear, current pedal
cadence, two wheels, number of gears)
– Behavior
• Dogs have behavior: barking, fetching, wagging
tail)
• Bycyles have behavior: braking, accelarating,
slowing down, changing gears
7
OOP Concept: Object (cont)
• Software objects are modeled after realworld objects in that they too have state
and behavior
• Software object:
– State  variables
– Behavior  methods, that is a function
(subroutine)
– Methods and variables is associated with an
object, that is reside in object
8
OOP Concept: Object (cont)
A Software Object, that have state and behavior
9
OOP Concept: Object (cont)
• Bicycle modeled as a software object:
– 10 mph, 90 rpm, 5th known as instance variable
because they contain the state for a particular object
– changeGears, brake, changeCadence known as
instance method, because they inspect or change the
state of a particular bicycle instance (object)
10
OOP Concept: Message
• The bicycle is useful only when another object (you)
interacts with it (pedal)
• Trough the interaction between objects, we can achieve
higher-order functionality and more complex behavior
• Software object interact and communicate by sending
message to another object
11
OOP Concept: Message
• Sometimes the receiver object need more
information to do, this information called
parameters
•You the sender object
•YourBicycle  the receiver object
•ChangeGears  the message, the
method to perform
•lowerGearinformation from You to
YourBicycle, the parameters needed by
the method
12
OOP Concept: Class
A class is a blueprint, or prototype, that defines the
variables and the methods common to all objects
of a certain kind
Class = method+attribute
The Bicycle class
13
OOP Concept: Class
14
Creating class
//Filename: Point2D.java
public class Point2D{
int x, y; // member variable
public Point2D() { x=0; y = 0;}
public Point2D(int nx, int ny)
{
setPoint(nx, ny);
}
// setter method
public setPoint(int nx, int ny)
{
x = nx;
y = ny;
}
// continue class Point declaration
// getter method
int getX() { return x; }
int getY() { return y; }
public static void main(String[] args)
{
// create object p
Point2D p = new Point2D();
p.setPoint(1, 5);
System.out.println(“x: “, p.getX()):
System.out.println(“y: “,p.getY()):
}
} // end of class declaration
15
Some Guidance for Creating class
• 1 file can contain >=1 class
• 1 file only can contains 1 public class
• Filename must be a public class name,
beware of case sensitive, remember that
Java is multiplatform
• Tips: It would be better to have every file
for every class you created
16
Class Access Level
Specifier
Class
Package
Subclass
Private

No specifier


protected



public



World

17
Methods
• No Default argument
• All parameter is passing by value
– How can we passing by reference?
• Support function name overloading, ie:
same name different function signature
(type of argument, number of argument,
order of argument)
18
Inheritance
• Reusability
• Top down:
– Being more specific
• Bottom Up:
– Find similarity
• Java Keyword:
extends
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Inheritance- Example
public class Point3D extends Point2D
{
int z;
public Point3D(int nx, int ny, int nz)
{
super(nx, ny); // called super class constructor
z = nz;
}
int getZ() { return z; }
void setZ(int nz) { z = nz; }
public static void main(String[] args)
{
Point3D p = new Point3d(10, 10, 3);
System.out.println(“(x, y, z): “+ p.getX() + “,” p.getY()
+ “,” + p.getZ());
}
}
20
Polymorphism
• Many shapes, 1 function behave
differently according to object instance
• “Late binding”, bind to instance not type
• In default all Java methods are
“polymorphic”
• Use “final” keyword to make “early
binding”, non polymorphic
21
Polymorphism-Example
//Filename: Point2D.java
public class Point2D{
int x, y; // member variable
public Point2D() { x=0; y = 0;}
public Point2D(int nx, int ny)
{
setPoint(nx, ny);
}
// setter method
public setPoint(int nx, int ny)
{
x = nx;
y = ny;
}
// continue class Point deklaration
// getter method
int getX() { return x; }
int getY() { return y; }
// overide method from class Object
public String toString()
{
return “x: “+x “, y: “+y;
}
} // end of class declaration
22
// Point3D.java
public class Point3D extends Point2D
{
int z;
public Point3D(int nx, int ny, int nz)
{
super(nx, ny); // called super class
constructor
z = nz;
}
int getZ() { return z; }
void setZ(int nz) { z = nz; }
// overide method from class Point2D
public String toString()
{
return super.toString() + “, z: “+ z;
}
23
public static void main(String[] args)
{
Point2D p1 = new Point2d(10, 10);
Point2D p2 = new Point3d(10, 10, 3);
printObject(p1); // x: 10, y: 10
printObject(p2); // x: 10, y: 10, z: 3
}
static printObject(Object o)
{
System.out.println(“Object content: “+ o);
// that is called o.toString()
}
}
24
Interface
• As container of abstract method
• Similar to class, except that all method are
abstract, just contain declaration.
• As the way of solved some problem that
need Multiple Inheritance feature
• As call back function
25
Interface - Example
// IUpdate.java
public interface IUpdate
{
public void UpdateProgress(int nPercent);
}
// Child.java, that called from Main class
public class Child {
IUpdate u;
public void addEventListerner(IUpdate iu)
{
u = iu;
}
public void run()
{
for (int i=1; i<=100; i++)
u.updateProgress(i);
}
}
26
// Main.java
public class Main implements IUpdate {
Child child;
public Main() // contructor
{
child = new Child();
// connect to child object
child.addEventListener(this);
// run child proses, and updating progress
child.run();
}
// implement method declared in Iupdate interface
public void UpdateProgres(int nPercent)
{
System.out.println(“Progess: “ +nPercent);
}
public static void main(String[] args()
{ new Main();}
}
27
Packages
• “A package is a collection of related
classes and interfaces providing access
protection and namespace management. ”
• 1 package is 1 subfolder in file system
• To organize file in project or library
• Keyword: package name;
28
Packages - Example
package com.binus.oop;
public class TestPackage
{
public static void main(String[] args)
{
System.out.println(“Contoh penggunaan package”);
}
}
• Catatan:
– Program diatas diberi nama TestPackage.java
– Program OOP.java terletak pada directory
x:\WebProg\OOP\com\binus\oop\TestPackage.java
– Setting classpath  SET CLASSPATH =
%CLASSPATH%\; x:\WebProg\OOP
– Compile : X:\webProg\OOP\com\binus\oop>javac
TestPackage.java
– Running: x:\>java com.binus.oop.TestPackage
29