public interface Scalarable {
		double scalarProduct(Point2D p);
	}
	
	public abstract class Point implements Scalarable {
		public Point() { }
		
		public String toString() {
			return "Some point. ";
		}
	}
	
	public class Point2D extends Point {

		double x;
		double y;
		
		public Point2D(double x, double y) {
			super();
			this.x = x;
			this.y = y;
		}
		
		public String toString() {
			return super.toString() + 
					"2D point. X - " + x + " Y - " + y;
		}
		
		@Override
		public double scalarProduct(Point2D p) {
			return Math.sqrt(x * p.x + y * p.y);
		}
	}