a4-polymorphism-arrays

Playing with polymorphism and arrays.

This assignment has two mandatory parts:

• 1. Shapes
• 2. Stats GUI

and two optional part (not graded):

• Standard Deviation
• Coding Trees

1. Shapes

Objectives

The objectives of this assignment are

1. To reinforce the concepts of inheritance and polymorphism
2. To give practice extending classes and implementing interfaces

Problem Statement

There are two sub-parts:

1. Implement RightTriangle and Square classes that inherit from Shape2D and implement all abstract methods. The class Rectangle serves as an example.
2. Implement the IShapePoints interface in the class Rectangle.

The main in TestShapes.java implements tests for the work in this lab.

Note how the static methods in TestShapes.java use parameters of Shape2D and IShapePOints only. Hence, this code will work with any class that inherits from the abstract class or implements the interface.

Once all elements are implemented, the corresponding lines in main can be uncommented and the output should be:

*** RightTriangle ***
1.0 x 2.0
area= 1.0
circumference= 5.23606797749979

*** Rectangle ***
1.0 x 2.0
area= 2.0
circumference= 6.0

*** Square ***
2.0 x 2.0
area= 4.0
circumference= 8.0

*** Reference point change ***
Reference point: (0.0, 0.0)
All points: [(0.0, 0.0), (1.0, 0.0), (0.0, 2.0), (1.0, 2.0)]

Setting reference point to (5.0, 10.0)
Reference point: (5.0, 10.0)
All points: [(5.0, 10.0), (6.0, 10.0), (5.0, 12.0), (6.0, 12.0)]

*** Change get reference point test ***
Got point (0.0, 0.0)
Changed point to (-10.0, 0.0)
Shape reference is (0.0, 0.0)
Comparing points is false (should be false)

*** Change set reference point test ***
Set reference to point (-1.0, -1.0)
Shape reference is (-1.0, -1.0)
Changed point to (1.0, 1.0)
Shape reference is (-1.0, -1.0)
Comparing points is false (should be false)

*** Square set width/height test ***
prior 1.0 x 1.0
after setWidth(5) 5.0 x 5.0
after setHeight(10) 10.0 x 10.0

Implementation: Inheritance

Study Shape2D.java and Rectangle.java.

Create a class RightTriangle in RightTriangle.java that represents a right triangle. It inherits from Shape2D and implements both abstract methods, a default constructor and a constructor taking width and height as arguments. Use Rectangle.java as an example.

Uncomment the corresponding line in TestShapes.java main to test the class.

Create a class Square in Square.java that represents a square. It inherits from Shape2D and implements both abstract methods, a default constructor and a constructor taking length as argument. Use Rectangle.java as an example. Since a square does not have an independent width and height, override setWidth() and setHeight() from the parent class so that both width and height are always the same.

Uncomment the corresponding line in TestShapes.java main to test the class.

Implementation: Interface

In the Rectangle class add implements IShapePoints to the class definition.

To implement the three methods of the interface, add an instance variable of type Point2D to the Rectangle class that will represent the reference point. Adapt any constructor to initialize this instance variable.

Implement getReferencePoint() and setReferencePoint() making sure you create a copy of the Point2D object.

Implement getAllShapePoints() to return the four points of the rectangle. Use the reference point as the lower-left point of the rectangle, e.g. the upper-right point of the rectangle would be (reference-x + width, reference-y + height).

Uncomment the corresponding lines in TestShapes.java main to test your implementation.

Reporting

In the markdown file Shapes.md add the UML class diagram including Shape2D, Rectanlge, RightTriangle, Square, IShapePoints, as an embedded image. Add JavaDoc and comments to all your class additions, classes and interfaces. Include a screenshot demonstrating successful execution of TestShapes.java.

2. Stats GUI

Objectives

The objectives of this lab is: To practice using arrays.

Problem Statement

Write a JFrame based GUI that enables the user to input a sequence of exam grades and then computes the average and the median of the grades entered.

To compute the median of a list of numbers, you must find the middle value -- i.e., that value for which there are the same number of smaller and larger. If there are an odd number of elements in the list, the median is the middle element. So, for the list

  10 20 45 65 76 78 88

the median would be 65. For a list with an even number of elements, you must take the average of the two middle numbers. So, for the list

  10 20 45 65 75 78 88 90

the median would be (65 + 75)/2 = 70. To solve this problem, it is necessary to store the individual grades in an array and then sort the array.

GUI Specifications

Elements and layouts of the GUI are implemented in src/StatsGUI.java.

The GUI contains an input JTextField, an output JTextArea, and two JButtons, one to show stats and one to clear the GUI (and start over). The user is prompted to enter grades into the JTextField. Pressing ENTER will add the grade. When the STATS button is clicked, the program sorts and displays the grades that were entered, plus their mean (average) and median. When the RESET button is clicked, the GUI should be cleared so that a new set of stats may be calculated.

Design Specifications

You need two Java classes for this project.

StatsGUI defines the graphical user interface. It should implement the ActionListener interface and should handle the following three actions:

• JTextField input: Pass the number in the text field to the Stats object
• STATS Button : Get the results from the Stats object and display them in the JTextArea.
• RESET Button: Clear the interface and create a new Stats object.

A partial implementation of this class is available at src/StatsGUI.java.

Stats should keep track of the grades that are typed in and should do the calculation of the mean and the median. It should contain the following elements:

• Instance variables. An int array is needed to store the individual grades. This should be declared private. Also, a private integer variable should be used to count the number of grades that have been stored in the array.
• Constructor Method. The public constructor method should instantiate the array to 100 elements and set the count to 0.
• The add(int) Method. This public method takes an int parameter, a grade, and inserts it into the next location in the array. It uses the counter variable to determine where the next element goes. Don't forget to increment the count after each insertion.
• The getMean() Method calculates the average of the numbers that have been inserted into the array. Use a for loop. What should the bound be for the loop?
• The sort() Method sorts the array into ascending order. This method is implement with code adapted from Try-This 5.1 in Java a beginner's guide.
• The getMedian() Method first sorts the first N elements of the array, where N is the number of grades that have been stored in the array. It then returns the median value as a double. You need to identify whether there are an even or odd number of elements in the array; and the center element.
• The toString() Method returns the list of sorted grades plus their average and their median. It uses string concatenation plus escape sequences, such as "\n" to format the output. This method will be called from the GUI.

You are provided a partial implementation of the src/Stats.java.

Reporting

In the markdown file Stats.md add the UML class diagram of StatsGUI and Stats, their dependencies and their relationships. Add JavaDoc and comments (where necessary) to all your class additions. Include a screenshot demonstrating successful execution and outputs of a computing stats of even and odd number of grades.

Reflection - Include a sentence or two about:

• what you liked or disliked,
• found interesting, confusing, challenging, motivating

while working on this assignment.

Optional: Standard Deviation

In the StatsGUI and Stats classes add functionality to compute the standard deviation.

Determine the Standard Deviation of the exam grades using the following method.

Raw score method for calculating standard deviation Consider the exam scores 8,25,7,5,8,3,10,12,9:

Determine N, which is the number of scores.
 
Compute the sum of X and the sum of Xsquared.
 
Then, calculate the standard deviation as illustrated below.
 
      score(X)   Xsquared

         8           64

        25          625

         7           49                  N = 9

         5           25

         8           64                  sum of X = 87

         3            9

        10          100                  sum of Xsquared = 1161

        12          144 
   
         9           81

       ---         ----

        87         1161



Standard Deviation 	= square root of((sum of Xsquared -((sum of X)*(sum of X)/N))/(N-1))

   			= square root((1161-(87*87)/9)/(9-1))
 
   			= square root((1161-(7569/9))/8)

   			= square root((1161-841)/8)

   			= square root(320/8)

   			= square root(40)

 Standard Deviation =  6.32 

Optional: Coding Trees

In this video Professor Altenkirch presents an object-oriented approach to represent equations. He uses Python. Implement the class hierarchy in Java.