1. Object Oriented Programming in JAVA
By:Srwa Mohammad

2. The Java Oops
Object Oriented Programming (OOP) is a programming concept used in several modern programming languages, like C++, Java and Python. Before Object Oriented Programming programs were viewed as procedures that accepted data and produced an output.
What is Class: Java is a purly an Object Oriented Language. Everything in java is an object. A Class does not hold any value unless and until it is used for object creation.
Definition: A class is a collection of data, stored in named fields, and
code, organized into named methods, that operates on that data.

3. The Java Class with method and parameter
class rectangle {
double l,w;
void get()
{ l=5; w=5; }
class Callmethod {
public static void main(String args[])
rectangle r=new rectangle(); r.get();
r.area(); }
void area() {
double a; a=l*w;
System.out.println("Area is:"+a); }}

4. The Java Constructor
Constructor:- A Constructor is a special method that does not have a return type and a has the same name as that of the class name. It means that a constructor can act as a normal method or function but it cannot return any value.
Every class must have at least one constructor.
If there are no constructors for your class, the compiler will supply a default constructor (no-arg constructor).
A constructor is used to construct an object.
A constructor looks like a method and is sometimes called a constructor method.
A constructor never returns a value

5. The Java Default Constructor Example
class box {
int l,w; box()
{ l=5; w=5; }
void show()
System.out.println("Length is:"+l); System.out.println("width is:"+w);
} }
class GradeBook
public static void main(String args[])
box b=new box(); b.show(); } }

6. Inheritance
 enables new objects to take on the properties of existing objects
. A class that is used as the basis for inheritance is called a superclass or base class. A class that inherits from a superclass is called a subclass
. Its done by using (extends) keyword

7. inheritance

8. Inheritance in Java class A { int i;int j; void showij(){
System.out.println("i and j:" +i+" "+j); }}
class B extends A {
int k;
void showk(){
System.out.println("K:" +k); }
void sum(){
System.out.println("i+j+k:" +(i+j+k));
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9. Inheritance in Java… class SimpleInheritanc{
public static void main(String args[]){
A objectA=new A();
B objectB=new B();
objectA.i=10 ; objectA.j=20; System.out.println("Contents of objectA :”);
objectA.showij();
System.out.println();
objectB.i=7; objectB.j=8; objectB.k=9;
System.out.println("contents of objectB“);
objectB.showij();
objectB.showk(); System.out.println();
System.out.println("Sum of i,j and k in objectB :”);
objectB.sum(); }}
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10. Compiler determines which method has to execute automatically.
Method Overloading
In java we can define many number of methods in a class with same name.
Defining two or more method with same name is known as “Method overloading”.
Compiler determines which method has to execute automatically.
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11. Method Overloading Example
class Rectangle {
void area(int length, int width ){
int a= length * width;
System.out.println("Area of Rectangle : " + a) }
void area(double length, double width) {
double b= length * width;
System.out.println("Area ofRectangle : " + b);}}
class RectangleDemo {
public static void main(String args[]) { Rectangle r1 = new Rectangle(); r1.area(10, 20);
r1.area(10.50, 20.50); }}
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12. Method Overriding
Method overriding: refers to idea of having a subclass contain a method with same name and parameters as a method in super class
Static methods can not be overriding

13. Overriding exmple class AA{ public void same(){
System.out.println(“this is class AA”); }}
class BB extends AA{
System.out.println(“this is class BB”);
public class Aga extends BB{
public static void main(String[]args){
Aga x=new Aga();
x.same()

14. overridden method using super keyword
If you write super.func() to call the method, it will call the method that was defined in the superclass.
class AA{
public void same(){
System.out.println(“this is class AA”); }}
class BB extends AA{
System.out.println(“this is class BB”);
public class Aga extends BB{
super.same();
System.out.println(“this is class Aga”); }
public static void main(String[]args){
Aga x=new Aga();
x.same()

15. polymorphism
Polymorphism: "Poly" means "many" and "morph" means "form". Polymorphism(many forms) is the ability of an object to become many different forms of object. Example: overloading, overriding, virtual functions
We use polymorphism with inheritance and, and the concept of it is “ one interface , multiple methods”.

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