ObjectOriented Programming Concept

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Object-Oriented Programming Concept

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Concepts of Object Orientation

• Objects and classes.
• method
• Message passing
• Inheritance

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What is an object?

• An object is..
• - anything real or abstract that store data and
  operations that manipulate the data.
• -a software bundle of variables and related
  methods (operations).
• -anything that supports the concept of a name.
• -an instance of a class.

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Messages

• Software objects interact and communicate with
  each other using messages

Customer object
Account object
Bank Object
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Using Object

• Objects give you two ways to do these things
• Manipulate or inspect its variables.
• Call its methods.

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• Referencing an Object's Variables
• objectReference.variableName
• Eg.
• int height new Rectangle().height
• Calling an Object's Methods
• objectReference.methodName(argumentList)
• or
• objectReference.methodName()
• Eg.
• rect_two.move(40, 72)
• int areaOfRectangle new Rectangle(100,
  50).area()

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Classes

• A class defines the attributes and operations
  common to all objects of a certain kind.
• A class is an object or a set of objects that
  share a common structure and a common behavior.
• A class is created when objects are used
  repeatedly.

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• Each class may have one or more lower levels
  called subclasses or one or more higher levels
  called superclasses.
• A unique object or a specific occurrence of a
  class of objects is called an instance.
• Classes define
• -attributes (state)
• -operations or methods (behavior).

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Generalization hierarchy

• The relationship among the classes, subclasses,
  and superclasses form a hierarchy.
• A generalization hierarchy is an object-oriented
  design tool used to show the relationships among
  the classes of objects.

TOOLBARS
BUTTON BARS
MENU BARS
SCROLL BARS
DROP-DOWN MENUS
SHORTCUT MENUS
LIST BOX MENUS
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• An operation, or service, is an activity that
  reads or manipulates the data of an object.
• Examples of operations include the standard
  mathematical, logical operations, input, output
  and storage operations associated with computer
  data.
• A method is the code used to perform the
  operation or service.
• For an object to do something, it must receive a
  message.

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• The message defines the interaction of the
  object.
• Everything an object can do is represented by the
  message.
• The message has 2 parts
• The name of the object to which the message is
  being sent.
• The name of the method that will be performed.

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• The trigger that causes the message to be sent
  may come from another object or an external user.
• The entire process of a trigger sending a
  message that causes an operation to occur is
  called an event.
• For example, if you click a button to save data,
  that action is the trigger. A message is sent to
  the disk to prepare for input. Writing the data
  to the disk is the operation. Saving is the event.

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• In object-oriented terminology, the data stored
  about an object is referenced by an attribute, or
  property.
• Attributes are identifying characteristic of
  individual objects such as name, size, or color.
• Attributes should not be confused with the data
  itself.
• For example, color is an attribute red is the
  data.

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An Object Structure Diagram
Object Structure Diagram
General Form of an Object Structure Diagram
Object name
Data Record
length number of fields sequence number
Object attributes
read write delete modify
Object methods
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Defining new classes

• To define a new Java class we must extend the
  class java.lang.Object
• eg.
• public class NameOfClass extends Object
• Or
• public class NameOfClass ..

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Final class

• Declares that the class cannot be subclassed.
• Two reasons
• to increase system security by preventing system
  subversion.
• good object-oriented design.
• Eg.
• final class ChessAlgorithm . . .

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Class attributes

• Attributes hold the state of an object.
• Eg. BankAccount object might include the
  attributes
• -accountNumber
• -accountOwner
• -overdraftLimit
• -balance

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Example class defination

• public class BankAccount
• private int accountNumber
• private String accountOwner
• private float overdraftLimit
• private float balance
• public void deposit(float amount) .
• public void withdraw( float amount) .
• public float getBalance()
• public void increaseOverdraft (float amount)
  .
• public void decreaseOverdraft (float amount)

Class name
Attributes
Methods
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Using packages

• To use existing classes in another package we use
  the import statement.
• -import package
• -import package.class
• -import package.
• Example
• -import java.awt
• -import java.awt.Button
• -import java.awt.

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Abstract classes

• Abstract classes are classes that embody coherent
  and cohesive, but incomplete concepts.
• Provide starting points for inheritance.
• eg. Motor vehicle can be motor car. Motor bike,
  motor boat, lorry etc...

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Creating abstract classes

• To make a class or method abstract we include the
  abstract keyword in the defination. Eg,
• public abstract class Shape

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Subclasses in Java

• To create a subclass of a Java class we use the
  extends keyword.
• We can only subclass one class at a time.( Java
  only supports single inheritance).
• public class Circle extends Shape
• ..

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Control Access

• There are 3 types
• public
• private
• protected

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• Private control access
• A classs private members are accessible
  only in the class methods.
• Public control access
• A classs public members are accessible
  anywhere that the program has a reference to an
  object of the class or one of its subclasses.
• Protected control access
• A classs protected members can be access by
  the class that define the members and its
  subclass.

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Exampleprivate

• class Wang
• private int ringgit, sen
• public Wang(int r, int s)
• ringgit r
• sen s
• System.out.println(Jumlah sen
  jumlahSen())
• private int jumlahSen()
• return 100ringgit sen
• class Aplikasi
• public static void main ( String args)
• Wang wang new Wang(5, 20)
• System.out.println(sen wang.jumlahSen())
  //Ralat

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Example public

• class Wang
• public int ringgit, sen
• public Wang(int r, int s)
• ringgit r
• sen s
• System.out.println(Jumlah sen
  jumlahSen())
• public int jumlahSen()
• return 100ringgit sen
• class Aplikasi
• public static void main ( String args)
• Wang wang new Wang(5, 20)
• wang.ringgit -100
• System.out.println(sen wang.jumlahSen())
  

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Class Methods (operations)

• Methods are the operations that an object can
  perform or suffer.
• BankAccount object might have methods
• -deposit()
• -withdraw()
• -getBalance()
• -increaseOverdraft()
• -decreaseOverdraft()

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Method Body

• super
• If a method hides one of its superclass's member
  variables, you can refer to the hidden variable
  through the use of the super keyword. Similarly,
  if your method overrides one of its superclass's
  methods, your method can invoke the overridden
  method through the use of the super keyword.

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• Eg
• class ASillyClass
• boolean aVariable
• void aMethod()
• aVariable true
• class ASillierClass extends ASillyClass
• boolean aVariable
• void aMethod()
• aVariable false
• super.aMethod()
• System.out.println(aVariable)
  System.out.println(super.aVariable)
• Output
• false
• true

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Constructor.

• All Java classes have constructors that are used
  to initialize a new object of that type. A
  constructor has the same name as the class.
• Typically, a constructor uses its arguments to
  initialize the new object's state. When creating
  an object, choose the constructor whose arguments
  best reflect how you want to initialize the new
  object.

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Encapsulation

• Encapsulation is the capability of an object to
  have data and functionality (methods) available
  to the user, without the user having to
  understand the implementation within the object.
• Encapsulation is the process of hiding the
  implementation and programming details of an
  object from its user, making those details
  transparent.
• Eg- stack (LIFO), the last item pushed (inserted)
  on the stack is the first item popped (removed)
  from the stack.
• The client of a stack class cares about what
  functionality a stack offers, but not about how
  that functionality is implemented.

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Inheritance (Pewarisan)

• The process of defining new classes by reusing
  the features of existing classes.
• Only the differences between the new class and
  the existing class needs to be defined.
• Can be found by looking for IS-A relationships
  between objects.
• Eg.

vehicle
is a
is a
boat
plane
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Inheritance example
Superclass
car
More generalised
Sports car
Estate car
More specialised
Sub-class
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Polymorphism

• Polymorphism allows an instruction to be given to
  an object using a generalized, rather than a
  specifically detailed, command.
• The same command will get different, but
  predictable result depending on the object that
  receives the command.
• While the specific actions (internal to the
  object) are different, the result would be the
  same.

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PolymorphismExample
SpaceObject draw()
LaserBeam
SpaceShip
Martian
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The Benefits of Object-Oriented Programming

• Reusability
• The classes are designed so they can be reused
  in many systems, or modified classes can be
  created using inheritance.
• Stability
• The classes are designed for repeated use and
  become stable over time.
• Easier design
• The designer looks at each object as a black box
  and is not as concerned with the detailed inside.
• Faster design
• The applications can be created from existing
  components.

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API Specification

• http//java.sun.com/j2se/1.3/docs/api/index.html