Lab 14 – Polymorphism, abstract classes, and inheritance

Due – Mar 16, before labs – 9:30am

Submit – To the Blackboard Assignment the source code for your new classes (ThreeDimensionalShapes, Sphere, and Pyramid).  In class, turn in the filled out worksheet – stapled and filled in. 

 

NOTE:  All classes must be properly documented.  They must compile and work properly with the parent (or super) classes from which they are derived.  You may need to use the Internet to find formulas to use.

Steps:

 

  1. Create a basic TestDriver class to use for testing your classes as you build them.

 

  1. Begin with the Sphere class.  Sphere will extend Circle which was used in the lecture just prior to break. 

 

  1. A sphere is like a circle in three dimensions.  All points on the outer surface are the same distance from the inner point, a distance referred to as the radius. 

 

  1. Create a Sphere class that extends Circle.  Will you need any additional attributes in Sphere? 

no

 

  1. Make sure that the constructor creates an appropriate description for this shape.  Since Circle has a specific constructor that takes in only a radius, but creates a Circle with the description “Circle”, what else will you need to do to properly construct a Sphere from a Circle?  Do it.

 

add an additional explicit value constructor

 

  1. Must you define a getArea() method for this class?  Compile the Sphere class without a getArea() method before answering.

 

no

 

  1. If you do not define a getArea() method and call the getArea() method for a Sphere object, what will the value returned represent?  Try it in your driver.  (Create both a Circle and a Sphere of the same radius and compare the results. )

the area of a Circle

 

  1. A Circle has an area representing the area enclosed by the perimeter of the Circle.  A Sphere could be considered to have an area which represents the surface of the Sphere.  Override the getArea() method in the Sphere to return the value of the surface area.  What formula will you use?  Can you use the getArea() method from Circle to not write so much code?  

4pr2 

yes

 

  1. Now write a getVolume() method for Sphere.  What formula will you use?  Be sure to test this method with your driver.

4/3 pr3

 

  1. Another design for the problem of building a Sphere is to build a ThreeDimensionalShape class as an abstract class extending either Shape or TwoDimensionalShape and then create the different kinds of three dimensional objects.  Assuming that ThreeDimensionalShape will extend Shape, what concrete (non-abstract) methods would you include in ThreeDimensionalShape and why?

 

just the constructor  - there are no explicit abstract methods in Shape that need to be made concrete in ThreeDimensionalShape

 

      And which abstract methods?  Why?

 

Should have these to guarantee that children provide them but are not required to do so

My example doesn’t have them.

protected abstract double getArea();

protected abstract double getVolume();

 

  1. Create the ThreeDimensionalShape class. 

 

  1. Now create a Pyramid class which extends ThreeDimensionalShape.  What attributes will you need to define your pyramid state assuming that the base of a Pyramid is square (or should I say Square)?  What volume formula will you use?  How will you calculate the surface area?  (Careful, the triangles that form the walls will not have the same “height” as the pyramid itself.  Think Pythagorean theorem.)

attributes – height, base (where base is the side of a square), angleHeight

volume – 1/3 *areaOfBase * height

surface area – 4*triangleArea + base*base

 

  1. Think about the Pyramid class and its relationship to other Shape classes.  Create the UML diagram (in JGrasp) of your classes.  How is Square related to Pyramid or what term do we use for that relationship?  How is that different from the relationship between the Pyramid and ThreeDimensionalShape?

Pyramid is a child of ThreeDimensionalShape

 

  1. Finally, think about the design of Sphere extending Circle, vs the creation of a new category of Shapes called ThreeDimensionalShape and the building of the Pyramid class.  Which design is better?  And why?

 

looking for an opinion to be followed by a class discussion