Due: Tuesday October 10, 2017 @ 8:00PM
This program is a solution to Problems 2 and 3 of Chapter 2 of Main (p. 95 – 96), but if there are any conflicts between the book and this document, rely on this document.
Create a Statistician class that maintains and reports information about a series of real numbers (type double in Java). Methods provided include the length of the series, the sum of the series, the mean, and the smallest and largest values. There is also a reset feature so that you can start a fresh series. Note that, UNLIKE the book, we are NOT keeping the most recent value.
Problem 3 has you provide a union method that adds the contents of this statistician and another statistician and returns a NEW statistician, as if all the values from the two had been put in the new one. This is like the + operator. It is good style to implement a += operator whenever you implement +. We'll call that add, in which the values of a statistician are added to an existing statistician. Doing this first makes the implementation of union easier and more efficient. Implement these two methods after you have the rest working.
We are providing you with a detailed outline for the statistician class, two console user interface classes to test the statistician, and a JUnit test class to test the statistician automatically. A more detailed discussion of JUnit is here. The class is in Statistician.java, which has extensive comments describing what each method does. The ConsoleMenuUI class lets you add numbers to the statistician and ask about its state. It is described in more detail below.
At first it might seem necessary to keep all the numbers in the series, but it is not. DO NOT keep all the numbers because you do not know how many will be input. Instead, the instance variables (fields) will hold just enough information to be able to provide the features of the class.
Suppose the input is the series: 5 15 10. You can easily determine the length of the series, the sum, the smallest value, and the largest value. The mean is the sum divided by the number of values. What changes when the value 30 is added to the series? You don't need the earlier values to answer the query.
Therefore, FOUR (AND ONLY FOUR) instance variables are enough to hold the state of the statistician class. Near the beginning of the class file, they are listed:
sumOfValuescountsmallestValuelargestValueThink about how those instance variables hold the state of the class. We have included a set of rules, the CLASS INVARIANT, that state what should be true of the instance variables BEFORE and AFTER every method executes. For example, if one or more numbers are in the series, smallestValue holds the smallest value in the series.
Understand the class invariant. It should be true after you construct the class object. Every method can rely on its being true. Every method should ensure that it is true when the method ends.
The ConsoleMenuUI class uses the Statistician class. It is an example of a driver program that provides an easy way to test the class's actions. It allows the user to create a statistician and then take the following actions:
q: quit the testing program
?: print this menu
+: add a value to the statistician
p: print a summary of the statistician values
r: reset the statistician
u: runs the union tests which also test clone and equalsYou can test your class with this driver. You do not write it. It runs, but doesn't do anything useful, as is.
Copy code and create project. Download the code here. There are four files in that directory:
Statistician.java The class code with some methods completed and some awaiting your implementation.ConsoleMenuUI.java The tester program described above.UnionDriver.java Runs the union tests including some checks on clone and equal. Called from ConsoleMenuUI.StatTest.java JUnit 4 tests that try to break the code with a wide variety of test cases.MAKE ALL YOUR CHANGES IN Statistician.java. DO NOT CHANGE METHODS NAMES. Start implementing the methods incrementally Implement each of the methods starting with the constructor and reset. Think about what happens in reset. You can call it from the constructor. insert is probably the hardest one to do. Maybe do the easy ones (the getters / accessors) that return simple values first.
Do NOT implement all the functions at once. As you implement each function, think about which instance variables it needs to access or change. Think about the state of the statistician and how it changes. Think of the class invariant as a checklist of what must be done to the instance variables to keep the state of the class correct.
When you have enough implemented to do some tests, run it. It will be boring until you implement the insert method.
Carefully test the class focussing on the functions you have implemented most recently and avoiding those you haven't completed yet.
Implement the other methods. Continue building methods until you have all of them except add and union implemented. Refer back to your class invariant to be sure it is true whenever you finish a member function.
Implement add and union. For the add method, you are implementing the actions for the statistician that is being assigned to (the c in c += a which is called in Java as c.add(a)). If you refer to count, that is c's count. To refer to a's count, use addend.count. Note that you have access to a's instance variables. Carefully consider what happens if a is empty, c is empty, or neither is empty. Test and implement the easy ones first. Carefully consider the properties the sum statistician should have. Consider all the instance variables. Getting it right takes some calculation.
When you have add working, you can implement union by making a clone of this statistician, using add on the clone with the other statistician, and returning the combined statistician.
Note that union and add can both throw a NullPointerException. However, that will happen automatically. You do not need to test for or throw this exception.
To run the JUnit tests, you must add the JUnit 4 library to your project. In Eclipse, highlight your project, right click it, and choose Build Path/Add Libraries.... Select JUnit then JUnit 4. Now when you run the JUnit test file, you should run as JUnit Test rather than Java Application. See the JUnit link above for more details.
Now that you have implemented all the member functions, check them more thoroughly using the various options in ConsoleMenuUI. Understand how to run the JUnit tests and do that. Run several detailed test cases. When you are satisfied that your program works as expected, submit your Statistician.java file.
Submit Statistician.java as the Statistician lab through Autolab
100 points total