Abstraction in Java

// Working of Abstraction in Java
abstract class Geeks {
    abstract void turnOn();
    abstract void turnOff();
}

// Concrete class implementing the abstract methods
class TVRemote extends Geeks {
    @Override
    void turnOn() {
        System.out.println("TV is turned ON.");
    }

    @Override
    void turnOff() {
        System.out.println("TV is turned OFF.");
    }
}

// Main class to demonstrate abstraction
public class Main {
    public static void main(String[] args) {
        Geeks remote = new TVRemote();
        remote.turnOn();   
        remote.turnOff();  
    }
}

abstract class Shape {
    String color;

    // these are abstract methods
    abstract double area();
    public abstract String toString();

    // abstract class can have the constructor
    public Shape(String color)
    {
        System.out.println("Shape constructor called");
        this.color = color;
    }

    // this is a concrete method
    public String getColor() { return color; }
}
class Circle extends Shape {
    double radius;

    public Circle(String color, double radius)
    {

        // calling Shape constructor
        super(color);
        System.out.println("Circle constructor called");
        this.radius = radius;
    }

    @Override double area()
    {
        return Math.PI * Math.pow(radius, 2);
    }

    @Override public String toString()
    {
        return "Circle color is " + super.getColor()
            + "and area is : " + area();
    }
}
class Rectangle extends Shape {

    double length;
    double width;

    public Rectangle(String color, double length,
                     double width)
    {
        // calling Shape constructor
        super(color);
        System.out.println("Rectangle constructor called");
        this.length = length;
        this.width = width;
    }

    @Override double area() { return length * width; }

    @Override public String toString()
    {
        return "Rectangle color is " + super.getColor()
            + "and area is : " + area();
    }
}
public class Test {
    public static void main(String[] args)
    {
        Shape s1 = new Circle("Red", 2.2);
        Shape s2 = new Rectangle("Yellow", 2, 4);

        System.out.println(s1.toString());
        System.out.println(s2.toString());
    }
}

// Abstract Class declared
abstract class Animal {
    private String name;

    public Animal(String name) { 
      this.name = name; 
    }

    public abstract void makeSound();

    public String getName() { 
      return name; 
    }
}

// Abstracted class
class Dog extends Animal {
    public Dog(String name) { 
      super(name); 
    }

    public void makeSound()
    {
        System.out.println(getName() + " barks");
    }
}

// Abstracted class
class Cat extends Animal {
    public Cat(String name) { 
      super(name); 
    }

    public void makeSound()
    {
        System.out.println(getName() + " meows");
    }
}

// Driver Class
public class Geeks {
  
    // Main Function
    public static void main(String[] args)
    {
        Animal myDog = new Dog("ABC");
        Animal myCat = new Cat("XYZ");

        myDog.makeSound();
        myCat.makeSound();
    }
}

// Define an interface named Shape
interface Shape {
    double calculateArea(); // Abstract method for
                            // calculating the area
}

// Implement the interface 
// in a class named Circle
class Circle implements Shape {
    private double r;    // radius

    // Constructor for Circle
    public Circle(double r) { 
      this.r = r; 
    }

    // Implementing the abstract method 
    // from the Shape interface
    public double calculateArea()
    {
        return Math.PI * r * r;
    }
}

// Implement the interface in a 
// class named Rectangle
class Rectangle implements Shape {
    private double length;
    private double width;

    // Constructor for Rectangle
    public Rectangle(double length, double width)
    {
        this.length = length;
        this.width = width;
    }

    // Implementing the abstract 
    // method from the Shape interface
    public double calculateArea() { 
      return length * width; 
    }
}

// Main class to test the program
public class Main {
    public static void main(String[] args)
    {
      
        // Creating instances of Circle and Rectangle
        Circle c = new Circle(5.0);
        Rectangle rect = new Rectangle(4.0, 6.0);

        System.out.println("Area of Circle: "
                           + c.calculateArea());
        System.out.println("Area of Rectangle: "
                           + rect.calculateArea());
    }
}