CSIT121 Assignment 2 Solution

File name: YourName _A2.java

Objectives:

Practice java programming with inheritance and polymorphism.

Implement the Shape hierarchy as shown in the above diagram

- Basically each two dimensional shape has an area method computes and returns the area of the two-dimensional shape.

- Each three dimensional shape other than the area (also known as surface area) method we also have a volume method; computes and returns, respectively, the surface area and the volume of the three-dimensional shape.

- Try to surf the internet to look for some formulas, for example, to compute the areas, the surface areas and the volumes … I did that too


A more detailed UML diagram is shown as follow: (Note that the #’s before the instance variables and the methods’ names mean “protected”)




Wow … so difficult to see; no worry, I will break it down bit by bit and explain what you have to do …

Let us explore the above UML diagram at the highest hierarchy; you can see that Shape is an interface class. Two abstract classes TwoD and ThreeD implement the Shape interface; TwoD also implements Recolorable interface and ThreeD also implements Resizable interface and we also have an enumeration data type to describe some of the colors:




Four possible shapes for TwoD: one value, for example the radius, is a circle shape; two values, for example the length and the width, is a rectangle; three values for example the three sides of a triangle (provided it can be formed), five values for trapezoid (one additional value was the height, as we need that to compute the area). In this class, you can see that we have four constructors to describe the four shapes, a copy constructor, some accessor and mutator methods and a toString method. Each 2D shape also has a color and the color can be changed (recolor method) during runtime. You can see we also define an enumeration type to specify the color of the shapes.

The following UML diagram shows the four concrete subclasses of TwoD:




Some methods just override the super class methods (same implementations)

Information defined in each of the subclasses should be obvious in definitions.

Now, let us look at the ThreeD class:



Three possible shapes for ThreeD: Just one value can determine the shapes of a sphere, a cube and or a tetrahedron. In this class, we only also have constructors, copy constructor, accessor methods, mutator methods and a toString method. For a 3D object, we can compute and return the volume too. Therefore we have one abstract method in this abstract class ThreeD.

ThreeD class also implements Resizable interface class. In this Resizable interface, other than the method resize, to reduce the size by certain percentage.

Refer to the above UML diagram for the three subclasses of ThreeD class:
(though the diagram to small, but the methods to be designed are obvious) Look for the surface area and volume formulas somewhere in internet to compute and to return their values, also don’t forget the two private methods
I have just mentioned 

Note that all 3D objects need to resize by a certain percentage.

Let us now explore the main class, i.e. main method is defined in this class

All shapes (2D or 3D) should be randomly generated and store them in an ArrayList of Shape’s.



You can see a few private class methods are defined in this class:

- a method generates and returns a positive integer, not too large - a method generates and returns a positive real number, not too large - a method generates and returns a color.
- a method generates and returns a TwoD shape
- a method generates and returns a ThreeD shape
- a method to display the objects stored in the ArrayList. Note that in the display method, you display the details of each shape object, i.e. the toString method for each of the classes only display a “brief” object info, display of area / volume / resizable/ recolor should be done in this method.

Convenient to your design, minor updates to methods or additional methods are allowed.

In the main method, you repeatedly generate an integer k (0 or 1 or 2). If k is 1 you construct a 2D object; if k is 2, you construct a 3D object and k is 0, you end the task. The following shows one of the possible displays:

Three objects were generated and stored in an array list and you displayed the list. You can see Shape 2 and Shape 3 were 2D objects, their colors are changed during runtime (you must make sure that the color is really changed to a different color); Shape 1, a cube, its sizes, area, volume were reduced by 24.2 % (this percentage was randomly generated).


IMPORTANT

Put all your classes in a file called YourName_A2.java and make sure that this file can be compiled and can be executed.
Upload ONLY this file to Moodle. ALL ZIP FILE SUBMISSION WILL BE REJECTED.

No re-submission will be allowed after grading.

In the above file, remember to put down your name and also the following declaration (some similar contents):

// Tell me if it is your own work, and whether you // have passed your program to your friends etc etc etc // and willing to accept whatever penalty given to you.

- Wrong file name -0.5 mark
- No declaration, no name etc -0.5 mark
- Failing to demo -1 mark
- Programs indentations and alignment of statements -0.5 mark
- Late penalty: -0.1 mark per hour.