import java.util.ArrayList;
import java.util.List;

public class Test {

    public static class Canvas {

        private List<GeometricFigure> figures;

        public Canvas() {
            figures= new ArrayList<GeometricFigure>();
        }

        public void print() {
            for (GeometricFigure figure : figures) {
                System.out.println(figure.getGirth());
            }
        }

        public void addFigure(GeometricFigure figure) {
            figures.add(figure);
        }

    }

    public static interface GeometricFigure {

        public Double getGirth();

    }

    public static class Square implements GeometricFigure {

        private double sideLength;

        public Square(double sideLength) {
            this.sideLength= sideLength;
        }

        @Override
        public Double getGirth() {
            return sideLength * 4;
        }

    }

    public static class Circle implements GeometricFigure {

        private double diameter;

        public Circle(double diameter) {
            this.diameter= diameter;
        }

        @Override
        public Double getGirth() {
            return Math.PI * diameter;
        }

    }

    public static void main(String... args) {
        Canvas c= new Canvas();
        //Canvas#addFigure takes as an input argument GeometricFigure and we are passing Square and Circle
        //That is because both are implementing GeometricFigure interface, so we don't care what actual
        //implementations we pass in, as long as the interface is respected.
        c.addFigure(new Square(4));
        c.addFigure(new Circle(4));
        //Prints 16 and 12.56 which is good. We don't care what are the implementations of the GeometricFigure
        //we only care about their girth
        c.print();

        //we add anonymously instantiated geometric figure
        c.addFigure(new GeometricFigure() {

            //We must override this method
            @Override
            public Double getGirth() {
                return 100.0;
            }
        });
        c.print();
    }

}