Guided Task - Working with the Java Libraries

Independent Task - Implement WolfScheduler

Independent Task: Finish `CourseRecordIO`

Now that we have the basic outline of CourseRecordIO you’ll implement the readCourse() method to process a single line from the input file and create an instance of the Course class. A correct implementation will pass the tests in CourseRecordIOTest. As part of our implementation of readCourse(), we’ll discuss how to test file I/O.

Learning Outcomes

Implement CourseRecordIO.readCourse()

Implement `CourseRecordIO.readCourse()`

To finish the CourseRecordIO class and pass all of the CourseRecordIOTests, you need to implement CourseRecordIO.readCourse(). The method receives a String which is a line from the input file. An example line might be:

CSC 116,Intro to Programming - Java,001,3,jdyoung2,MW,0910,1100

CSC 216,Software Development Fundamentals,601,3,jctetter,A

You can use a Scanner to process the String parameter. You must break the line up into tokens by using the comma character (e.g., ',') as a delimiter. A delimiter is a string that is used to separate or break apart a larger string. The default delimiter for Scanner is white space. You can change the delimiter using the Scanner.useDelimiter() method. After updating the delimiter, any call to Scanner.next() will return the token before the next delimiter. So for our example,

CSC 216,Software Development Fundamentals,601,3,jctetter,A

the first call to Scanner.next() would return a string "CSC 216", the second call to Scanner.next() would return a string "Software Development Fundamentals", etc. When reading the values for credits, startTime, or endTime, you can use Scanner.nextInt().

Once you break the line into tokens, you can construct a Course object and return it from the method.

There are two places where code that you work with may lead to an exception for invalid values in the input string:

NoSuchElementException or InputMismatchException: if you receive these when processing the input, catch them and throw an IllegalArgumentException to the caller (which in this case is CourseRecordIO.readCourseRecords()).
IllegalArgumentException: when constructing a Course with invalid values, the Course class will throw an IllegalArgumentException. In this case DO NOT catch the exception! Instead, let the exception propagate to the caller (which in this case is CourseRecordIO.readCourseRecords())

Use the fields and constructors of the Course class to help you determine what type each token should be. The tokens will always be in the order of:

name,title,section,creditHours,instructor,meetingDay,startTime,endTime

name,title,section,creditHours,instructor,A

If the meeting days string is NOT “A”, then you’ll need to read in the last two tokens. If there are any additional tokens after the expected last one, an IllegalArgumentException should be thrown.

The high level structure of the method is provided in the pseudocode, below. You do not have to implement the method this way, but it will be useful for getting started.

//TODO - Add Javadoc here!
private static Course readCourse(String line) {
   construct Scanner to process the line parameter
   set the delimiter to ","
   
   try {
      read in tokens for name, title, section, credits, instructorId, and meetingDays and store in local variables
	  
      if meetingDays is "A"
         if there are more tokens
            throw IAE
         otherwise
         return a newly constructed Course object
      
      otherwise
      read in tokens for startTime and endTime
      if there are more tokens
         throw IAE
      return a newly constructed Course object
   } catch any exceptions and throw a new IllegalArgumentException
   
   //Remember to close the scanner on all possible paths out of the method - that's not in the pseudocode
}

Make sure that all your tests are passing before continuing with the Guided Project!

File I/O Testing Overview

Let’s take a quick look at the CourseRecordIOTest class to discuss how we are testing CourseRecordIO.

There are three test methods and a private helper method.

Two of the test methods test the CourseRecordIO.readCourseRecords() method.
CourseRecordIOTest.testReadValidCourseRecords() considers an input file with valid lines and one duplicate. When the file is processed there should be 13 Course objects in the ArrayList and their toString() output should match the constants validCourse* at the top of the test class. CourseRecordIOTest.testReadInvalidCourseRecords() considers an input file with invalid lines. Each line is invalid in a different way as per the requirements. The README.txt file describes why each line is invalid and may be useful for finding any bugs in your code.

The last test method, CourseRecordIOTest.testWriteCourseRecords() tests the CourseRecordIO.writeCourseRecords() method. The private helper method checkFiles() will check that the actual output file matches the expected output file. The expected output file was provided. You can review the tests in more detail as testing is covered in the class. You will see file I/O again and these tests will be a useful reference for future projects!

Troubleshooting

There are several places where you may run into trouble when implementing the CourseRecordIO.readCourse() method. The troubleshooting section provides an overview of how to resolve the challenges. You should also refer to your course text book on the chapters related to File I/O, post questions to Piazza, and attend office hours to help with the implementation of this method!

Unable to Reset Files

You may run into a java.lang.AssertionError: Unable to reset files when executing the CourseRecordIOTest.setUp() method. This method is resetting course_records.txt with the starting values needed for the tests. Other tests in the system may overwrite course_records.txt, so the starter_course_records.txt file is used to rest the original file. There are several possibilities that you should investigate if you run into this error:

Close all of the files that may be open in Eclipse or in your file system. If the file is being processed by another application, the JVM may not be able to open it.
Close the Scanner in all possible paths in CourseRecordIO. If you do not release the Scanner on the file, the file may still be considered in use for a time, even if the test stopped execution.
Make sure that all files use the *.txt extension.
Restart Eclipse. This will release any file handles that are attached to open files.

Resource Leak

If you receive a CheckStyle notification about a resource leak on your Scanner, make sure that you separate any program statement Scanner s = new Scanner(nextLine).useDelimiter(","); into two program statements. Using the two methods chained together leads to CheckStyle misunderstanding the flow of the methods.

Reference: Staging and Pushing to GitHub

GitHub Resources:

Check Your Progress

We’ve finished CourseRecordIO. Before moving on to the next portion of the Guided Project, complete the following tasks:

Make sure that all fields, methods, and constructors are commented.
Resolve all static analysis notifications.
Fix test failures.
Commit and push your code changes with a meaningful commit message. Label your commit with “[Implementation]” for future you!

Guided Task - Working with the Java Libraries

Independent Task - Implement WolfScheduler

Guided Project 1 - Software Development Practices and Tools