Description
Objective
In this lab, you will practice using exceptions and assertions.
Working alone or in a group of 2, you will create two small programs that demonstrate how to
use exceptions and assertions.
Preparation
• Review the discussion on exceptions from class.
• Review the recursive code for calculating the Fibonacci numbers from the debugging lab.
• Prepare pseudocode to implement a non-recursive binary search on an array of integers.
Procedure
Set-up
1. Get the recursive code for calculating the Fibonacci numbers working in a project.
Lab steps
Part 1 – Exceptions
1. Revise the Fibonacci code as follows to be able to limit the depth of the recursion:
• Add two parameters to the method: one to say the maximum number of levels of recursion
should be allowed and the second to say how deep you are now in the recursion
• When the code calls itself recursively, increment the parameter on how deep you are into
the recursion
2. Create a custom-made exception called MaximumRecursionDepth that extends the RuntimeException
class. The new exception should include a String message and an int that is the depth of recursion reached. Ensure that your custom-made exception has two methods available:
• getMessage() to return the string message
• getDepth() to return the integer depth that was reached at the time of the exception
3. Modify your Fibonacci code to throw a MaximumRecursionDepth exception when the recursion
depth exceeds the value of the parameter for the maximum number of levels of recursion.
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Part 2 – Assertions
1. Write (non-recursive) code to perform a binary search on a sorted array. You can get help from
the Internet for this part; just be sure to cite any sources that you use. This step is not the
critical one of the lab.
2. Add the following assertions:
• a loop precondition
• a loop invariant
• a postcondition
3. Ensure that your assertions are working.
Questions
We usually want you to re-use existing code and infrastructure whenever possible. Why might you
create your own exception?
We added parameters to the Fibonacci method. However, those parameters aren’t very meaningful to
a general user. What would you do to the code to make it more accessible for a general user?
How would you recommend for someone to develop a loop invariant?
How can loop invariants help you in programming, even if you don’t include them directly as assertions
in your code?
Reporting
1. In one file, list
• The members of your team.
• The answers from the Questions section of the lab.
2. Generate a PDF from the document.
3. Submit the PDF in Brightspace and all your Java files in Brightspace in the Lab/Lab 4 section.
Assessment
The assessment will be on a letter grade and will reflect how well you implemented the exceptions and
assertions, how much you re-used existing code, and how well you demonstrate that you can take the
work of this lab and apply it to another situation (the questions section).
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