Algorithms and OOD (CSC 207 2014F) : EBoards
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Related Courses: [CSC 152 2006S (Rebelsky)] [CSC 207 2014S (Rebelsky)] [CSC 207 2014F (Walker)] [CSC 207 2011S (Weinman)]
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Overview
Polymorphism
(define square (lambda (x) (* x x)))
square
works for integerssquare
works for doublessquare
works for complex numbers#define square(x) ((x)*(x))
Inheritance
In Java
public class GrinnellStudentEmployee
extends GrinnellStudent
Encapsulation
Suppose we are representing points on the plane
public class Point
{
// +--------+------------------------------------------------------
// | Fields |
// +--------+
double x;
double y;
// +---------+-----------------------------------------------------
// | Methods |
// +---------+
public double distanceFromOrigin()
{
return Math.sqrt(x*x + y*y);
} // distanceFromOrigin
} // class Point
Two approaches for the client
public class GeoLocator
{
public static void main(String[] args)
throws Exception;
{
Point pt1 = GoogleMaps.makePoint("Grinnell, IA");
Point pt2 = GoogleMaps.makePoint("Minneapolis, Minisoda");
// I need to figure out which of point 1 and point 2 is closer
/ to the origin
if (pt1.distanceFromOrigin() < pt2.distanceFromOrigin())
giveDirectionsTo(pt1);
else
giveDirectionsTo(pt2);
}
}
// I need to figure out which of point 1 and point 2 is closer
/ to the origin (Note: For non-negative x and y,
// x < y iff sqrt(x) < sqrt(y).)
if (pt1.x*pt1.x + pt1.y*pt1.y < pt2.x*ptx + pt2.y*pt2.y)
giveDirectionsTo(pt1);
else
giveDirectionsTo(pt2);
Which is better?
What happens if we decide that we should represent points with radius and angle?
public class Point
{
// +--------+------------------------------------------------------
// | Fields |
// +--------+
double radius;
double theta;
// +---------+-----------------------------------------------------
// | Methods |
// +---------+
public double distanceFromOrigin()
{
return radius;
} // distanceFromOrigin
} // class Point