Assignment № 3 Implementing a Subclass and Abstract Methods

Definition 1. Inheritance is the process by which one class (type), the derived class, is defined
by extending the behavior of an existing class (type), the base class. In Java the existing class
is called the superclass and the new class is called a subclass. The Object class in Java is
the cosmic class; that is, every class inherits the Object class. In today’s lab session, you will
define three classes: Polygon, a superclass that describes a polygon, Triangle, a subclass of
the Polygon class, and TriangleDemo, a program to test your implementation of the superclass
and subclass.
The Polygon Class
Definition 2. A polygon can be defined as a geometric object consisting of a number of points
(called vertices) and an equal number of line segments (called sides), namely a cyclically ordered set of points in a plane, with no three successive points collinear, together with the line
segments joining consecutive pairs of the points.
The Polygon class will consist of an array of type Point2D.Double, named vertices, as its
instance variable. This class will be an abstract class. View the online Java API documentation
to find the package in which Point2D.Double is defined. When declaring the instance variable
vertices, use the protected access specifier. This class will consist of the following methods:
1. public Polygon() : a default constructor that creates a degenerate polygon consisting of
one point, (0,0).
2. public Polygon(Point2D.Double[ ]) : a parameterized constructor that takes an array of
points as an explicit parameter and creates a polygon.
3. protected static double distance(Point2D.Double , Point2D.Double ) : an auxilliary method
used to find the Euclidean distance between two points. Given points p1 = (x1, y1) and
p2 = (x2, y2), the Euclidean distance between them is given by the formula:
p1p2 =
q
(x1 − x2)
2 + (y1 − y2)
2
(1)
4. public abstract double area(); : an abstract method which when implemented computes
the area of the polygon.
Assignment № 3 Page 1
5. public double perimeter() : an instance method that computes the perimeter of the polygon.
6. public Point2D.Double[ ] getVertices() : returns an array of points that are vertices of the
polygon.
7. public void setVertices (Point2D.Double[ ]) : modifies the vertices of a polygon using the
points in the array, the explicit parameter of the method.
The Triangle Class
Definition 3. A triangle is a three-sided polygon. It consists of three vertices.
Define a class Triangle, a subclass of the Polygon class. The Triangle class will consist of
the following methods:
1. public Triangle(Point2D.Double[]) : a parameterized constructor that takes, as an explicit
parameter, an array of three points.
2. Implement the abstract area() method defined in the superclass, Polygon.
s =
p1p2 + p2p3 + p1p3
2
(2)
a =
p
s (s − p1p2) (s − p2p3) (s − p1p3) (3)
where s, is half the perimeter of the triangle, pipj , is the Euclidean distance between points
pi and pj , and a is the area of the triangle.
3. Override the public String toString() method so that it returns a string representation of the
triangle in the form {(x1, y1),(x2, y2),(x3, y3)}, where (x1, y1), (x2, y2), and (x3, y3) are the
vertices of the triangle.
The TriangleDemo Class
Define a class, TriangleDemo, consisting of only one method, the main method, that does the
following:
1. Creates a triangle whose vertices are (9, 9), (11, 14) and (17, 13).
2. Creates a second triangle whose vertices are (5, 6), (5, 46) and (14, 6).
3. Prints the coordinates of the first triangle and its area and perimeter to the nearest ten
thousandths.
4. Prints the coordinates of the second triangle and its area and perimeter to the nearest ten
thousandths.
Since we have not studied exceptions and exception-handling, we will assume that points used
to create each triangle are non-collinear.
Assignment № 3 Page 2
Additional Requirements
Do not define any other class or implement any additional method other than those described in
this handout. Compile and run your program to make sure that it works. Write header comments
for each class using the following Javadoc documentation template:
/**
* Explain the purpose of this class; what it does <br
* CSC 1351 Lab # 3
* @author YOUR NAME
* @since DATE THE CLASS WAS WRITTEN
*/
For the Triangle class, after the @since line, add the following Javadoc:
* @see Polygon
For the TriangleDemo class, after the @since line, add the following Javadoc:
* @see Triangle
Remove all Netbeans-generated Javadoc documentation. Add Javadoc documentation for each
instance variable and method in both Polygon and Triangle classes. Run the Javadoc utility to
make sure that it generates documentation for the Polygon and Triangle classes. Locate your
source files, Polygon.java, Triangle.java and TriangleDemo.java and enclose them in a zip file,
YOURPAWSID_lab03.zip, and submit your lab assignment for grading using the digital dropbox
set up for this purpose. Here is a sample program interaction, where ... denotes a numeric
value to the nearest ten thousandths:
Listing 1: Sample Run.
1 The first triangle: {(9.0,9.0),(11.0,14.0),(13.0,17.0)}
2 perimeter: ...
3 area: ...
4
5 The second triangle: {(5.0,6.0),(5.0,46.0),(14.0,6.0)}
6 perimeter: ...
7 area: ...
Assignment № 3 Page 3