Main.java

abstract class Shape {
    String color;

    Shape(String color) {
        this.color = color;
    }

    abstract double calculateArea();

    void displayColor() {
        System.out.println("Color: " + color);
    }

}

class Circle extends Shape {
    double radius;

    Circle(String color, double radius) {
        super(color);
        this.radius = radius;
    }

    @Override
    double calculateArea() {
        return Math.PI * radius * radius;
    }
}

class Rectangle extends Shape {
    double width, height;

    Rectangle(String color, double width, double height) {
        super(color);
        this.width = width;
        this.height = height;
    }

    @Override
    double calculateArea() {
        return width * height;
    }
}

public class Main {
    public static void main(String[] args) {
        // Shape shape1 = new Shape("Green");//ERROR! cannot instantiate abstract class
        Circle circle = new Circle("Red", 5);
        Rectangle rectangle = new Rectangle("Blue", 4, 6);

        System.out.println("Circle Area: " + circle.calculateArea());
        circle.displayColor();

        System.out.println("Rectangle Area: " + rectangle.calculateArea());
        rectangle.displayColor();
    }
}