01. introduction to classes and objects

8/8/2019 01. Introduction to Classes and Objects

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Introduction to Classes and

Objects

Ridwan Rismanto, S.ST


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Declaring Class

GradeBook class

Display a welcome message

Receive course name as an argument and displaying

it as the part of welcome message

Store the course name in GradeBook object

Using methods to set and obtain the course name

Initialization using constructor

GradeBookTest class

Has the main method to use GradeBook class


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Declaring Class (2)

Each class declaration that begins with

keyword public must be stored in a file that

has the same name as the class, andends with .java extension.


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GradeBook class


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GradeBookTest class


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Inside the GradeBook class

Keyword public is an access modifier

Keyword void indicates that a method

doesnt have a return value Class GradeBook isnt an application

because it doesnt have a main method

It will be error if you try to execute


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Inside the GradeBookTest class

This class is an application because it has mainmethod that will be executed first by the JVM

The main method is special because it is static

Allows us to call the method without creating anobject

In this application, we call GradeBooksdisplayMessage method.

Keyword new creates a new object of the class The objects method can be called using dot

separator (.)


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UML

Graphical representation scheme for

modelling object oriented systems

Class name Class attributes

Class operations (methods)


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UML for GradeBook class


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Class GradeBook declaration with

one method that has a parameter


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Output


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Inside the GradeBookTest class

A scanner named input for reading the

coursename from user

A variable passing From users input to variable nameOfCourse

And then passing it to displayMessage

method


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Updated UML for GradeBook class


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Instance Variables, setMethods

and getMethods A Class normally consists of methods and

attributes

Attributes are represented as variables ina class declaration


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GradeBook Class with an Instance Variable,

a setMethod and a getMethod


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GradeBookTest Class That

D

emonstrates Class GradeBook


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Output


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Access Modifiers

Declaring instance variables with access

modifier private is known as data hiding

variable courseName is encapsulated (hidden) in the

object and can be accessed only by methods of theobject's class

Private

Can only be accessed by methods that is a member

of the class

Public

Can be accessed by methods outside the class


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Initialing Objects with Constructors

Each class we declare can provide a constructor

A method that will be executed first when we create

an object

Java automatically provides default constructor in anyclass

Constructor must have the same name as the

class

Usage example : we want to define a defaultvalues for our classs attributes


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GradeBook class with a constructor that

receives a course name


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Constructor used to initialize GradeBook

objects


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01. introduction to classes and objects

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