Java

An abstract class is a class marked with the abstract keyword. It, contrary to non-abstract class, may contain abstract - implementation-less - methods(An abstract class may contain abstract methods (methods without code or body)). It is, however, valid to create an abstract class without abstract methods.

An abstract class cannot be instantiated. It can be sub-classed (extended) as long as the sub-class is either also abstract, or implements all methods marked as abstract by super classes.

Abstraction can be achieved with either abstract classes or interfaces .

// Abstract Class in Java Programming
abstract class Shape {
    abstract void draw();

    void message() {
        System.out.println("Message From Shape");
    }
}

class rectangleShape extends Shape {
    @Override
    void draw() {
        System.out.println("Draw Rectangle Using Length & Breadth..");
    }
}

public class App {
    public static void main(String args[]) {
        rectangleShape o = new rectangleShape();
        o.draw();
        o.message();
    }
}