To illustrate the object-oriented programming concepts introduced in this chapter, lets consider generic 2D shapes. There are many types of shapes including circles, triangles, squares, rectangles, pentagons, and so forth. All of these shapes have certain characteristics in common, since they are closed 2D shapes having an enclosed area and a perimeter of finite length. Create a generic shape class having methods to determine the area and perimeter of a shape, and then create an appropriate class hierarchy for the following specific shapes: circles, equilateral triangles, squares, rectangles, and pentagons. Then, illustrate polymorphic behavior by creating shapes of each type and determining their area and perimeter using references to the generic shape class.