Abstract Class In Java Language

Abstract Class :

A method with method body is called concrete method In general any class will have all concrete methods A method without method body is called abstract method A class that contains abstract method is called abstract class It is possible to implement the abstract methods differently in the subclasses of an abstract class These different implementations will help the programmer to perform different tasks depending on the need of the sub classes Moreover, the common members of the abstract class are also shared by the sub classes

The abstract methods and abstract class should be declared using the keyword abstract We cannot create objects to abstract class because it is having incomplete code Whenever an abstract class is created, subclass should be created to it and the abstract methods should be implemented in the subclasses, then we can create objects to the subclasses

• An abstract class is a class with zero or more abstract methods

• An abstract class contains instance variables & concrete methods in addition to abstract methods

• It is not possible to create objects to abstract class

• But we can create a reference of abstract class type

• All the abstract methods of the abstract class should be implemented in its sub classes

• If any method is not implemented, then that sub class should be declared as “abstract‟

• Abstract class reference can be used to refer to the objects of its sub classes

• Abstract class references cannot refer to the individual methods of sub classes

• A class cannot be both “abstract‟ & “final‟

• eg : final abstract class A // invalid

Program 1 : Write an example program for abstract class Using abstract methods and classes abstract

class Figure
{
double dim1;
double dim2;
{
dim1 = a;
dim2 = b;
}
abstract double area (); // area is now an abstract method
}
class Rectangle extends Figure {
Rectangle (double a, double b) {
super (a, b);
}
double area () // override area for rectangle {
System.out.println ("Inside Area of Rectangle");
return dim1 * dim2;
}
}
class Triangle extends Figure {
Triangle (double a, double b) {
super (a, b);
}
double area() // override area for right triangle {
System.out.println ("Inside Area of Triangle");
return dim1 * dim2 / 2;
}
}
class AbstractAreas {
public static void main(String args[])
{
// Figure
f = new Figure(10, 10); // illegal now
Rectangle r = new Rectangle(9, 5);
Triangle t = new Triangle(10, 8);
System.out.println("Area is " + rarea());
System.out.println("Area is " + tarea());
}
}