The previous relationship is used at the class level
to describe
relationships between two similar classes. If we create objects of two such
classes we refer to their
relationship as an ``is-a'' relationship.
In this and the following figures, objects are drawn
using rectangles
with round corners. Their name only consists of lowercase
letters.
is-a
circuit
point
Since the class Circle is a
kind of class Point, an instance of Circle, say acircle, is a point.
Consequently, each circle behaves like a point. For example, you can
move points in x direction
by altering the value of x. Similarly, you move circles in this direction by
altering their x value.