Introduction to java and oop

Recall
• What is meant by OOP?
• What are classes and objects?
• What are the differences between OOP and Procedure oriented
Programming?

Java
• Oop paradigm
Java is a computer programming language that is class-based, object-
oriented and makes maximum out of it
• “Write once run anywhere”
Java applications are typically compiled to bytecode (.class file) that can run
on any Java virtual machine(JVM) regardless of computer architecture

C Vs java
• int
• Char
• Float
• double
‚Exactly the same as of left side‛
Data Types

C Vs java
• Conditional control structures
– If
– If else
– Switch
• Loops
– for
– while
– Do while
Control Structures

C Vs java
int sum(int a, int b)
{
Int c;
c=a + b
return c;
}
sum(12,13)
functions

C Vs java
int a[] = {1000, 2, 3, 50};
int a[10];
int a[]={1,2,3,4}// not a preferred way
int[] a={1,2,3,4} //preferred way
int[] myList = new int[10];
Arrays

C Vs Java
Output
printf(“ value of a = %d”,a);
Printf(“a = %d and b= %d”,a,b);
Input
scanf(“%d ", &a);
Scanf(“%d”,&a,&b);
Output
System.out.println(“hello baabtra”);
Input
Scanner sc = new scanner(System.in);
int i = sc.nextInt();
(import java.util.Scanner)
Input / Output
Out
In
System
Println()
Print()
Write()
PrintStream

C Vs java
char str*+ = ‚hello‛;
‚String is character array‛
String str=‚Hello‛;
‚String is an object ‚
Strings

C Vs java
• As we are well aware c program
execution begins at main() function
Eg: main()
{
Printf(‚hello world‛);
printHello();
}
Same as C, differs that the main() will be
a member function of some class.
Name of the class and file should be
the same.
class myFirstProgram
{
public static void main(String[] args)
{
System.out.println(‚hello baabtra‛);
}
main() function

What’s New in java?
• OOP concepts
• JVM and Platform independency
• Automatic garbage collection

OOP Concept
• Object-oriented programming (OOP) is a style of programming
that focuses on using objects to design and build applications.
• Think of an object as a model of the concepts, processes, or
things in the real world that are meaningful to your application.

Objects in real world
• Object will have an identity/name
 Eg: reynolds, Cello for pen. Nokia,apple for mobile
• Object will have different properties which describes them best
 Eg:Color,size,width
• Object can perform different actions
 Eg: writing,erasing etc for pen. Calling, texting for mobile

Objects
I have an identity:
I'm Volkswagen
I have different properties.
My color property is green
My no:of wheel property is 4
I can perform different actions
I can be drived
I can consume fuel
I can play Music
I have an identity:
I'm Suzuki
I have different properties.
My color property is silver
My no:of wheel property is 4
I can perform different actions
I can be drived
I can consume fuel
I can play Music

How these objects are created?
• All the objects in the real world are created out of a basic prototype
or a basic blue print or a base design

Objects in the software world
• Same like in the real world we can create objects in computer
programming world
–Which will have a name as identity
–Properties to define its behaviour
–Actions what it can perform

How these objects are created
• We need to create a base design which defines the properties and
functionalities that the object should have.
• In programming terms we call this base design as Class
• Simply by having a class we can create any number of objects of
that type

Definition
• Class : is the base design of objects
• Object : is the instance of a class
• No memory is allocated when a class is created.
• Memory is allocated only when an object is created.

How to create class in Java
public class shape
{
private Int width;
private Int height;
public Int calculateArea()
{
return x*y
}
}

public class shape
{
private Int width;
private Int height;
{
return x*y
}
}
Is the access specifier

public class shape
{
private Int width;
private Int height;
{
return x*y
}
}
Is the keyword for
creating a class

public class shape
{
private Int width;
private Int height;
{
return x*y
}
}
Is the name of the class

public class shape
{
private Int width;
private Int height;
{
return x*y
}
}
Are two variable that
referred as the
properties. Normally
kept private and access
using getters and setters.
We will discuss getters
and setters later in this
slide

public class shape
{
private Int width;
private Int height;
{
return x*y
}
}
Is the only member
function of the class

How to create objects in java
shape rectangle = new shape();
rectangle.width=20;
recangle.height=35;
rArea=rectangle.calculateArea();
This is how we create an
object in java
rectangle
Height:
width:
calculateArea()
{
return height*width;
}

How to create objects in C++
rectangle.width=20;
recangle.height=35;
Is the class name

rectangle.width=20;
recangle.height=35;
Is the object name which
we want to create

rectangle.width=20;
recangle.height=35;
“new” is the keyword used
in java to create an object

rectangle.width=20;
recangle.height=35;
What is this???
It looks like a function
because its having pair of
parentheses (). And also
its having the same name
of our class . But what is it
used for ??
We will discuss it soon .
Just leave it as it is for now

How to create objects in Java
rectangle.width=20;
recangle.height=35;
Setting up the property
values of object
“rectangle”
rectangle
width: 20
Height: 35
calculateArea()
{
return width*height;
}

How to create objects in Java
rectangle.width=20;
recangle.height=35;
Calling the method
calculateArea()
rectangle
width: 20
Height: 35
calculateArea()
{
return 20*35;
}

Example
Class : shape
Height:35
width:20
Object rectangle
calculateArea()
{
Return 20*35
}
Height:10
width:10
Object square
calculateArea()
{
Return 10*10;
}
Member variables
Height
width
Member function
calculateArea
{
return height*width;
}

What we just did was
• Created an object
• Same like we declare variable. eg: int a;
• And assigned values for it
recangle.height=35;
same like we assign variable value. eg: a=10;
Rectangle
Width:
Height:
calculateArea()
{
return
width*height;
}
Rectangle
width: 20
Height: 35
calculateArea()
{
return 20*35;
}

So, Can i assign values into an object at the time
of its creation(known as initialization)??
Something that we do with variables like int a=14;

So, Can i assign values into an object at the time
of its creation??
Something that we do with variables like int a=14;
‚Yes, you can . For that purpose we use something called
constructor‛

Constructors
• Constructors are just a method like any other methods in the
class but having the same name of the class.
• It is used to initialise the properties of an object
• will not have any return type, not even void
• If no user defined constructor is provided for a class, the implicit constructor
initializes the member variables to its default values
– numeric data types are set to 0
– char data types are set to null character(‘0’)
– boolean data types are set to false
– reference variables are set to null

public class shape
{
private Int width;
private Int height;
private Int calculateArea()
{
return x*y
}
}
How to create Constructors

public class shape
{
private Int width;
private Int height;
shape(int height,in width)
{
this.width=width;
this.height=height;
}
private Int calculateArea()
{
return x*y
}
}
Shape rectangle=new shape(20,35);
Constructor
Rectangle
width: 20
Height: 35
calculateArea()
{
return 20*35;
}
How to create Constructors

Access Specifier
• Access specifies defines the access rights for the statements or
functions that follows it until another access specifier or till the
end of a class.
• The three types of access specifiers are
–Private
–Public
–Protected
–default

Getters and Setters
• There are several occasion we need to validate the data when assigning values
into it
• For eg: rectangle.width=-10;
rectangle.height=-12;
• Suppose i want to check whether the user enters a negative value and if so i
wish to assign 0 to the properties
• In such scenarios we will create a method to do the above said actions
Rectangle
width: -10
Height: -12
calculateArea()
{
return -10*-12;
}

Getters and Setters
• Getters and setters are simply two function that gets and sets the value of
class properties.
• Setter
– Rectangle.width=15; // Normally this is how we set the values of class properties.
Rectangle.setWidth(15); // calling a method named ‚setWidth‛ so that the
method will set the property width to 15
• Getter
– Rectangle.width; // Normally this is how we get the values of class properties.
Rectangle.getWidth(); // calling a method named ‚getWidth‛ so that the method
will get the value of the property width

public class shape
{
private Int width;
private Int height;
Int calculateArea()
{
return x*y;
}
Public setWidth(int a)
{
if (a>0)
width=a;
else
width=0
}
Public Int getWidth()
{
return width
}
}
How to create getters and setters

public class shape
{
private Int width;
private Int height;
Int calculateArea()
{
return x*y;
}
{
if (a>0)
width=a;
else
width=0
}
{
return width
}
}
Setter function

public class shape
{
private Int width;
private Int height;
Int calculateArea()
{
return x*y;
}
{
if (a>0)
width=a;
else
width=0
}
{
return width
}
}
Getter function

OOP features
»Abstraction
»Encapsulation
»Polymorphism
»Inheritance

Abstraction
• Act of representing essential features only and hiding the implementation
details
• For example, a car would be made up of an Engine, but one does not need
to know how the diverse components work inside.
• In our example of class shape ; the users only have to create objects of type
shape like rectangle,square etc.
• And for finding out the area he dont really have to think about how the area
is calculated. He only need to know calling the method calculateArea will
reuslt him with the area.

Encapsulation
• Wrapping up of data(properties) and code(methods) into a single unit is
known as encapsulation
• Encapsulation also includes the process of hiding all the data and methods
within a class from outside world by restricting access to the object's
components.
• In programming languages, encapsulation is accomplished by using private
access specifier

Inheritance
• Is the process where one object acquires the properties of another.
• Inheritance is a type of relationship
– Ex: BMW is a Car
• Reusability of code – Methods and properties of parent class will be
accessible to child class
• In java inheritance is achieved by using keyword ‚extends‛
• Java supports only single inheritance

public class shape
{
protected Int width;
protected Int height;
Int calculateArea()
{
return x*y;
}
int drawShape()
{
system.out.println(“shape”)
}
}
public class threedimensionalshape extends shape
{
private Int depth;
Int calculateVolume()
{
return width*heigh*depth;
}
}
Example

Example
• Shape rectangle = new rectangle();
• threedimensionalshape cube =new threedimensionalshape()
Rectangle
Width:
Height:
calculateArea()
{
Return width*height
}
cube
Width:
Height:
depth
calculateArea()
{
Return width*height
}
Int calculateVolume()
{
return
width*height*depth;
}

Polymorphism
• Polymorphism is the ability to take more than one form using
the same name
– Eg : function overloading, Operator overloading(not supported in java)
• Functions can have same name but different implementations
• There are two types of polymorphism
–Static
–Dynamic

public class shape
{
Int calculateArea(int width, int height)
{
return width * width;
}
Float calculateArea(int radius)
{
return (22/7) * radius * radius
}
}
public class example
{
Public static void main{
shape sh =new shape();
System.out. Println(sh.calculateArea(20, 10));
System.out.println(sh.calculateArea(10));
}
}
Output:
200
314.28
Example – Static polymorphism

public class shape
{
Void drawShape()
{
system.out.println(“Shape”)
}
}
public class ThreeDshape extends shape
{
Void drawShape()
{
system.out.println(“3D shape”)
}
}
public class example
{
Public static void main{
shape sh =new shape();
ThreeDshape tds =new ThreeDshape ();
Sh.drawShape();
sh=tds;
Sh.drawShape;
}
}
Output:
Shape
3D shape
Example – Dynamic polymorphism

Static and Dynamic polymorphism
• Achieved using Overloading
• Signature difference
• Inheritance not required for
implementation
• Decision at compile time
• Early binding
• Achieved by Overriding
• Uses inheritance and virtual
functions
• Inheritance required for
implementation
• Decision at runtime
• Late binding

Questions?
‚A good question deserve a good grade…‛

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Introduction to java and oop

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Introduction to java and oop