Inheritance and Polymorphism allows one class to inherit attributes and behaviors of another class. The subclass inherits all data attributes and methods of the superclass. The subclass can add new functionality, use inherited functionality, or override inherited functionality. Inheritance is declared using the "extends" keyword. Each class has one superclass, creating a hierarchy. Method overloading occurs when two methods have the same name but different arguments, while method overriding occurs when two methods have the same name and arguments but different implementations. Access modifiers like private, protected, and public determine whether subclasses can access attributes and methods of the superclass.

1. Inheritance and Polymorphism
M. Raihan
Computer Science and Engineering Discipline , Khulna University

2. What is inheritance ?
 Inheritance is a fundamental Object Oriented
concept
 A class can be defined as a "subclass" of another
class.
 The subclass inherits all data attributes of its
superclass
 The subclass inherits all methods of its
superclass
 The subclass can:
 Add new functionality
 Use inherited functionality
 Override inherited functionality

3. Declaration
 Inheritance is declared using the "extends" keyword
 To access Super Class from Sub Class we use super keyword.
Example :
class SuperClass{
// rest of codes
}
class SubClass extends SuperClass{
// rest of codes
}

4. Inheritance Hierarchy
 Each Java class has one (and only one) superclass.
 Inheritance creates a class hierarchy
Class A
Class B
Class D Class E
Class C
Class F

5. A Program
public class SuperClass {
Scanner sc = new Scanner(System.in); // Here we take input from Keyboard
public double CircleArea(){
double pi=3.1416,num1=0,r=0,CircleAreaResult=0;
num1=sc.nextDouble(); // num1 input taken
r=sc.nextDouble(); // r input taken
CircleAreaResult = pi*num1*(r*r);
return CircleAreaResult;
}
public double TriangleArea(){
double base,hight,TriangleAreaResult = 0;
base=sc.nextDouble(); // Here base input taken keyboard
hight=sc.nextDouble(); // hight input taken from keyborad
TriangleAreaResult = 0.5*base*hight;
return TriangleAreaResult;
}
public void Result() {
double Result1,Result2;
Result1= CircleArea();
Result2= TriangleArea();
System.out.println(“Circle Area : “+Result1+”nTriangle Area : “+Result2);
}
}

6. A Program (continue)
public class Main extends SuperClass{
public static void main(String[] args) {
SuperClass sp= new SuperClass();
sp.Result();
}
}

7. Some Methods
toString(): return a string that contains the name
of the object’s class and a hash value
equals(): determines if two variables point to the
same object (more shortly).

8. Access Modifiers
 Private data fields are not accessible to derived classes
 Protected visibility allows data fields to be accessed either by the
class defining it or any subclass.
 In general, it is better to use private visibility because
subclasses may be written by different programmers and
it is always good practice to restrict and control access to
the superclass data fields
 Members (variables and methods) declared with public
visibility are accessible, and those with private visibility
are not

9. Method Overloading
When 2 or more methods in a class have the same method
names with different arguments, it is said to be method
overloading.
Overloading does not block inheritance from the superclass.
Overloaded methods must have different method
signatures.

10. Example
public class Calculate{
public void circle(){
}
public int circle(int a){
return ;
}
public float circle(float a){
return ;
}
}

11. Method Overriding
When a method in a class has the same method
name with same arguments as that of the
superclass, it is said to be method overriding.
Overriding blocks inheritance from the superclass.
Overridden methods must have same signature.

12. Example
public class SuperClass{
public void calculate(int a, int b){
int c=a+b;
}
}
public class SubClass extends SuperClass{
public void calculate(int a, int b){
int c;
if(a>b)
c=a-b;
else
c=a+b;
}
}

13. Thank You