Writing a Java application with class structure

Your first Java programming assignment is to write an application that uses a class. The goal is to start by giving you some practice with Java syntax and making sure that you understand the class concept.

Before starting this assignment, you should should become familiar with the Java programming environment on sirah.

You may also use Java compilers on other systems if your prefer, or a programming environment such as J++ or Cafe'. But if you use a programming environment, do not use it to generate code for you. Also see the tutorial materials for links to download an editor such as JavaEdit or TextPad for use on a PC.

Writing the programs

Choose one of the following two sets of programs to write.

Choice 1: Writing and Testing a class Candy

Design and implement a class to represent pieces of candy. There will be three instance variables to represent properties of the candy:

• String shape; // this may take values such as "square", "round" or "blob".
• Color c;
• String flavor; // values such as "vanilla", "chocolate", or "yuck".

Write a constructor method that takes three arguments that are used as values to initialize the instance variables.

You should also write the following public methods.

• three "set" methods - one to assign each instance variable
• either three "get" methods to return the values of the instance variables, or a method called "toString" that returns a string describing the three properties of the candy.
• a method called "combine" which takes two arguments of type Candy and returns a result of type Candy. This method should combine the properties of the two arguments to return a new third candy. You can decide how to combine them. For combining shapes and flavors, you can arbitrarily pick a result shape and flavor, and in at least one case you should refuse to combine incompatible shapes and flavors by returning an exception. For combining colors, you could average together the red, blue and green values of the two colors. (Check the API Color class to see how to find out the RBG values of a Color.)
• You may design additional methods if needed by your test application program below.

You must also write a test program for this class:

Design an application that prompts the user to type in the shape, color, and flavor of at least two pieces of candy. Create an instance of the Candy class for each one. Combine the two pieces to get a third piece of candy and either use the "get" methods or the "toString" method to print out a description of the result.

Show a couple of runs of the program. Be sure to demonstrate a case of successfully combining candies and also one which doesn't because the combine gives an Exception.

Choice 2: Writing and Testing a class DataSets

Design and implement a class to represent a set of data, that is a number of experimental numbers representing some value. You will need an instance variable to keep the data:

• double [ ] data;

Write a constructor method that takes two arguments: an int n that is used to create the data array to be of length n, and an array of doubles of length n. After creating the data array, the constructor should copy the argument array to the data array to initialize it.

You should also write the following public methods.

• a method that returns data.length.
• a method that computes the arithmetic mean (average value) of the array values and returns it.
• a method to compute and return the standard deviation of the values of the array. Here is a definition of the mean (called mu in the diagram) and standard deviation for an array of length n:
  
  where the notation "sigma x" is to be interpreted as summing all the elements of the array and the notation "sigma x squared" means to first square each element of the array and then sum them.
• a method combine that takes two data sets and produces a third one. You should combine the two datasets only if the arrays have the same length and give an exception otherwise. When the arrays are the same length, you can combine them by averaging together each pair of array elements.
• You may design additional methods if needed by your test application program below.

You must also write a test program for this class.

Design an application that prompts the user to type in at least two sets of double values. Create an instance of the DataSet class for each one. Compute the mean and standard deviation of each dataset and print the results. Then combine the two DataSets to get a third one and print out its mean and standard deviation.

Show a couple of runs of the program. In a case where you refuse to combine some datasets, be sure to demonstrate that part.

What to put on the homework page as the submission of your homework

Submit your assignment by linking the description of your program, a link to the Java source code and a small file showing sample output run (like my .run files) to your homework page.

For how to write a description of your homework and document your program, and other information, please see these homework guidelines.

Grading

For this assignment, there will be a total of 15 points. These will be separated into partial points of 5 and 10 as follows:

• 5 points are for the assignment description, comments in the code, and documentation in general.
• 10 points are for writing Java code in a good style that is easy to understand, that your programs meet the requirements and produce nice output. Some of the points in this partial will be for effort and uniqueness.