Description
Objectives:
Practice java programming with inheritance and polymorphism.
Task (5 marks)
2
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”)
3
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:
4
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:
5
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)
6
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.
7
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).
Note that the list may be empty …
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.
8
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.
