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Is-A relationship
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.