SE-1011 Software Development 1
Lab 6: Spirographer

Outcomes

• Develop additional proficiency with the Java language
• Implement mathematical expressions and formulas using the Java Math class
• Use both standard Java library classes as well as classes developed externally
• Incorporate conditional control statements, such as if, for, and while, into a Java program to affect program control flow.

If you ever played with the Spirograph toy as a kid, you are already familiar with the shapes it can draw, like so:

Your assignment is to write a Java application that draws similar shapes with the aid of the WinPlotter class that was written by me (this is an example of a user-written class that we'll be discussing soon in class).

The "shape" above is really a curve that mathematicians call an epitrochoid. The coordinates (x,y) of any point on the curve are given by the following parametric equations:

where R, r, and d are values that govern the overall shape of the curve. For a particular curve, you choose arbitrary values for R, r, and d (for example, 51, 99, and 75 for the curve shown above). You also choose a fixed value for n (100 in the curve above), which governs the "precision" of the curve. In the equations above, t is the independent (parametric) variable, meaning that x and y are both functions of t. Thus, as t varies, the values for x and y can be calculated for any point on the curve.

Your math professor would say that t varies continuously between negative infinity and positive infinity. Computers (and calculators), however, can only evaluate functions for discrete, finite values of the independent variable. Thus, you can only compute discrete values for x and y for each discrete value of t. For some range of values of t (for example, from 0 to 10000), you can compute 10001 values for x and y. To plot the curve, you connect the successive x,y points with straight lines. If the points are close together, the straight lines are very short, and you get a decent approximation to the "ideal" mathematical curve.

Detailed requirements

Your program must consist of a main class called Spirographer, in a package named msoe.se1011.<your msoe email name>

Declare a constant to represent n and initialize it to a value of 100. Unlike variables, constants have all UPPERCASE names and are usually declared at the top of a program - in fact, outside of any method. Declare your constant above the main() method but within the class braces. DO NOT use a hard-coded value for 100 anywhere else in your program; use this constant instead.

In your program's main() method, prompt the user to enter:

• A value for R (from 50 to 100)
• A value for r (from 1 to 100)
• A value for d (from 50 to 100)

Your must request these values using the JOptionPane.showInputDialog method. Use 3 separate while or do-while loops to surround the entire sections of code that processes these inputs.

In all three sections, implement the logic that ensures that the inputs are not null, not empty, and within the specified range.

• If null, it implies that the user pressed Cancel, in which case you should silently exit the program.
• If empty, it implies that the user pressed OK with no input. In this case, print a specific error message using JOptionPane.showMessageDialog and repeat the prompt by continuing the surrounding while-loop.
• If the value is not empty, but out of range, print a different error message and repeat the prompt (by continuing the surrounding while-loop).
• If the user enters illegal characters that cannot be converted to numeric values, you program may crash.

Once your program acquires and validates the input values, create an instance of the WinPlotter class. Then implement the following pseudocode to configure the drawing window:

1. Set the size of the WinPlotter window to 500 by 500 pixels.
2. Set the plot boundaries to -300,-300,300,300.
3. Set the background to a color of your choice.
4. Set the initial pen color to a color of your choice. (Note that you must supply values for red, green and blue color components which make up the composite color, and the values vary from 0-255. All 0 values produce the color black, while all 255 values produce white).
5. Set the title to something containing your name.

Next, evaluate the equations above for x and y using a value of t=0. Use the moveTo() method of WinPlotter to move the "drawing pen" to these coordinates within the drawing window. Note: read the API documentation for the Math class to determine how to compute sines and cosines.

DO NOT use a hard-coded value for pi in your code. Instead, use the predefined value from the Math class.

Use the use a for-loop to iterate the parameter t from 1 to 10000. Within the loop, evaluate the equations for x and y. For each pair of computed values, use the drawTo() method of WinPlotter to draw a straight line to each successive coordinate. Change the pen color every 100 steps through the loop (hint: use the modulo operator to determine when to change pen color). Use the Math.random() method to generate a random value between 0 and 1, and then use the approach discussed in the textbook to scale that to a value between 0 and 255 - the values you supply to the setPenColor() method of WinPlotter.

Near the bottom of the drawing window, use the WinPlotter printAt() method to print a formatted message similar to: "Plot for R=51, r=99, d=75"

After the for-loop, prompt the user to run again by using the JOptionPane.showConfirmDialog, which produces the dialog below. If the user presses "Yes", repeat the entire program from the start (you'll have to surround everything with a while-loop).

Lab Submission (due date in WebCT)

Submit your assignment following these instructions:

1. You do not need to hand in a flowchart, but you may find it helpful to create one before you start coding.
2. Upload your .java file through WebCT (assignment "Lab 6: Spirographer").

Your grade will be based on the following criteria:

• Meeting requirements; your program must compile and run. If you have trouble, you must come to see me. If you don't and you submit a program that does not compile or produce meaningful results will receive a grade of no higher than 50, even after reworking your program.
• Technical quality of your program. Technical quality consists of formatting, commenting, and following coding style guidelines I have been telling you about in class and in grading comments in your previous labs.
  • Every conditional test must be fully commented to let the reader know what you are doing in the case where the if condition is satisfied, as well as the case where the else or else if condition is satisfied instead.
• Spelling and grammar (Eclipse even has a built-in spell checker - make use of it!)
• Timeliness of submission as stated in the course policies.