Exercise : Debug ZipCode Case Study

In this exercise we will practice the jGRASP debugger using the Case Study example from the end of Chapter 6. To download this example, follow these steps:

1. Go to the class web page and click the "Textbook" link.
2. Find the section labeled "Code Files" and click the "code files" link.
3. This will bring you to a directory listing that includes an entry for each chapter. Click the link for "ch06".
4. You want to download and save the files ZipLookup.java and zipcode.txt. Right-click the file names and choose the option to save the link in whatever folder you have been using for lab work. Make sure to save them in the same folder.
5. Compile and run ZipLookup.java in jGRASP. You might try using your own ZIP code and a relatively small radius like 0.5 miles. The program takes a while to run because it has to search a large data file.

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Exercise - jGRASP Debugger

• The debugger can be particularly helpful to understand a program that processes a large data file. In this exercise are going to debug the ZipLookup program.
• This program makes two passes through the data file. First it looks for the target zip code in the method named find. Then it shows all matches in the method named showMatches. We want to debug showMatches.
• The data file has a total of 43,191 zip codes in it, so it is not practical to have it display all of the data. That's why it's important to have good debugging skills to be able to selectively stop the program at certain points to see what is going on.
• Ask a TA for help if you have trouble setting or clearing break points or otherwise completing this exercise.

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Exercise - jGRASP Debugger

• We'll debug the program as it searches for all zip codes with 0.3 miles of the White House, at zip code 20500. Run the program with those input values:

  What zip code are you interested in? 20500
  And what proximity (in miles)? 0.3
  
  20500: Washington, DC
  zip codes within 0.3 miles:
      20045 Washington, DC, 0.26 miles
      20500 Washington, DC, 0.00 miles
      20501 Washington, DC, 0.27 miles
      20502 Washington, DC, 0.27 miles
  

• Now let's see what is true just before the while loop in the showMatches method executes. Set a break point on the while loop itself. Then debug to find lat1 and long1 (latitude and longitude of the White House ZIP code).

  lat1		38.894781
  long1		-77.036122

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Exercise - jGRASP Debugger

Clear your previous break point and set a new break point inside on the printf inside the if. Then hit the resume button that looks like a play button and fill in the table below with the values for zip, lat2, and long2.

zip	lat2	long2
20045	38.896599	-77.0319
20500	38.894781	-77.036122
20501	38.89872	-77.036198
20502	38.89872	-77.036198