This document provides an introduction to object-oriented programming concepts including classes, objects, instance variables, and methods. It defines a class as a template or blueprint from which objects are made. Instance variables store values that define the state of each object. Methods implement operations on objects and are defined with the same name and parameters across all objects from the same class. The document discusses creating objects, declaring instance and static variables, defining instance and static methods, and passing arguments to methods by value and reference.

1. Introduction to Class
Object-Oriented Programming

2. Module Introduction
1.
Classes and Objects
2.
Instance variables
3.
Methods
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3. #1 – Classes and Objects

Class declaration

Constructors

Creating objects
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4. Creating Class

The template or blueprint from which
objects are actually made.

Syntax:
class ClassName{
//definition of class
}

All code that you write in Java is inside a
class.

Classes can be built by extending other
classes
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5. Constructor - how to instance an object?

Same name as the class.

A class can have more than one constructor.

A constructor can take zero, one, or more parameters.

Has no return value.

Always called with the new operator.

Use for initializing variables and invoking any methods that
may be for initialization.

If a class does not have an explicit constructor, a default
constructor (no-argument) is provided.
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6. Dissecting the Rectangle class
Name of class
1. Use Naming rules
Data member
2. Always captain first letter
• WhatConstructor
data does it need to
3. Use Noun for naming
know?
•
Define the way to
instance object
1. Same name as the
class name
Methods
2. Like function in C but
• Whathave no do? value
can it return
1. Like function in C
2. Use Verb for naming
3. Always lower first letter
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7. Creating objects (instance object)

An object must be created before using in a program.
1.
Declare a variable to store the object reference.
1.
Objects can only be manipulated via references
2.
Creating an object.
1.
Using the new operator in conjunction with a call to a constructor
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8. #2 – Data Member

Instance Variables

Class Variables
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9. Instance variables

The values of those variables
define the state of object.

All instances of a class have
the same instance variables
 May have different values
inside them.

Has an “access modifier”
associated with it.
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10. Example of Instance variables
recA
length = 3.0
width = 4.0
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recB
length = 6.4
width = 4.7
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11. Class Variables (Static Variables)

Variable that is accessed
without using an object of a
class.

Declare using the static
keyword.

Only one copy of a static
variable is shared by all the
objects of the class.
 Change in the value of static
variable is reflected by all the
objects of the class.
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12. Example of Static Variables
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13. #3 - Methods

Definition

Instance Method

Calling method and Passing Arguments by Value.

Calling method and Passing Arguments by Reference.

Static Methods

Variable Argument Methods
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14. Method

A method is defined as the actual implementation of an operation
on an object.

Syntax:
access_specifier modifier datatype
method_name (parameter_list)
{
//body of the method
}

The method name should begin with
a lowercase verb and follow with
a proper noun.
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15. Instance Method

A function defined in a class

Invoked by an instance object
and can access instance
variables

Provide a mechanism for
accessing the private data
stored in an object
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16. Invoking Methods

Using the '.' operator

Syntax:
 <the object reference> ‘.’ <the method to be invoked>
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17. Calling method and Passing Arguments by Value.

Value from calling method is passed as an argument to the
called method.

Any change made to that passed value in the called method
will not modify the value in the calling method.

Variables of primitive types (int, float ..) are passed by value.
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18. Example of Calling method and Passing Arguments by
Value.
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19. Calling method and Passing Arguments by Reference.

Called method to change the value of the parameter passed
to if from the calling method.

When references are passed as parameters, the caller can
change the values stored but not the reference variables.
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20. Example of Calling method and Passing Arguments by
Reference
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21. Static Methods

Methods that do not operate on objects.
 Can be called without creating any objects of the class.

Call static method, supply the name of the class.

Declared using the static keyword.

Can directly refer only to static variables and other static
methods of the class.

Cannot refer to non-static methods and variables
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22. Example of Static Methods
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23. static methods usage

When a method doesn't need to access the object state

When a method only needs to access static fields of the
class.
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24. Variable Argument Methods

Allow calling a method with variable number of arguments.
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25. That’s about all for today!

Classes and Objects

Instance variables

Methods
Thank you all for your attention and patient !