Resources

• Java ArrayList API

Background

The goal for this activity is to re-write the solution to our earlier statistics activity using ArrayLists instead of arrays. Recall that in the array version of the code the user was required to provide a command line argument specifying how many values they intended to enter. This was necessary so that we could allocate an array with enough capacity to store the input.

With ArrayLists, we don't need to know how many elements we will store in advance. There is no need to ask the user to provide this information.

Part 1: Review

If you didn't complete the earlier lab, download the solution from Canvas and look over the code. Make sure you understand how the array-based solution works.

Part 2: Re-Write

Re-write Stats.java and StatDriver.java with the following changes:

• Stats.java should be re-written so that both methods take ArrayLists of Doubles instead of double arrays. In all other respects the functionality should be the same.
• StatDriver.java should store user input into an ArrayList of Doubles instead of an array. Your main should keep reading in numbers using nextDouble as long as hasNextDouble returns true. (The user can indicate that no more numbers will be entered by pressing CTRL-d in the terminal.)
• StatDriver.java should no longer expect an integer value as a command line argument. Instead, the user should be able to provide a string on the command line indicating whether they want to calculate the mean ("mean") or the standard deviation ("std"). If no argument is provided, the mean should be calculated. Here are some examples of interacting with the completed program:

  spragunr@L25001:~$ java StatDriver mean
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  Mean: 2.50
  spragunr@L25001:~$ java StatDriver std
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  StdDev: 1.12
  spragunr@L25001:~$ java StatDriver
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  Mean: 2.50
  

Once you have completed and tested your code, create a zip file containing StatDriver.java and Stats.java files and submit it through WebCat. Web-CAT will not run Checkstyle tests on your submission.

Part 3: If You Have Extra Time

1. Add a median method to your Stats.java class. (The Collections.sort method will probably be helpful.)