This class exercise is designed to familiarize students with exceptions and file I/O in Java.

• Basic knowledge of Java exceptions, including checked exceptions, unchecked exceptions, and the use of try-catch, throw, and throws.
• Familiarity with program command-line arguments in Java.

• LO2.b: Define, throw, and propagate exceptions appropriately in a software solution.

In your notes, clearly answer the following questions. These instructions assume that you are logged into the Odin server.

NOTE: If a step requires you to enter in a command, please provide in your notes the full command that you typed to make the related action happen. If context is necessary (e.g., the command depends on your present working directory), then please note that context as well.

1. Use Git to clone the repository for this exercise onto Odin into a subdirectory called cs1302-ce04:

   $ git clone --depth 1 https://github.com/cs1302uga/cs1302-ce04.git
   

2. Change into the cs1302-ce04 directory that was just created and look around. There should be multiple Java files somewhere in the directory structure. You may want to execute the find command on the src directory for a quick, easy-to-read view of the directory contents.

   • What are the fully qualified names for the classes contained in the Java files?
   • What is the path to the default package for source code relative to the cs1302-ce04 directory?

3. The directory you downloaded contains a Java implementation of the Unix cat utility. Remember, the commands you have been executing in Unix are just programs that were installed by the system administrators. MyCat.java works similarly to cat but was written by your instructors and will be compiled by you. Before compiling, use the Unix cat utility to print the contents of MyCat.java to the terminal. Write the command you used to do this in your notes.

4. Read through the Java code in MyCat.java and Printer.java. Note, there is a dependency between the two files. Based on the dependencies, which .java file must be compiled first?

5. From the cs1302-ce04 directory, try to compile each Java file separately, specifying bin as the default package for compiled code.

   Note In this step, you may encounter a compile-time (syntax) error. Hint: the error should not be a "cannot find symbol" error. If it is, you will need to adjust your compilation command.

   Answer the following in your notes about the compile-time error:

   • In what file is the error?
   • On what line in the source code is the error?
   • How does Java describe the error?
   • Fix that specific compile-time error. There may be logical errors with the code--do not fix them at this time.
   • Briefly describe your fix.

1. From the cs1302-ce04 directory, use your freshly compiled MyCat program to display the contents of Printer.java by passing the relative path to Printer.java as a command-line argument. HINT: When a program interacts with files, it is relative to the current working directory in which the program is being run. That is, the directory you are in when you type the java command. For a Java program, relative paths are relative to that directory.

2. Take a moment to note the similarties between using MyCat and the Unix cat utility.

3. From the cs1302-ce04 directory, use the MyCat program to display the contents of standard input. HINT: Read through the code to see what command-line argument you might use to read from standard input. This may seem weird at first, but the program should allow you to type in lines of text to standard input. When you complete a line by hitting return, the program will print the line to standard input. The program will terminate once it reaches the end of the file. What does that mean for standard input? You can trigger the end of file (a.k.a. the EOF) by pressing C-d.

4. From the cs1302-ce04 directory, run the MyCat program with no command-line arguments. A run-time exception should occur. Answer the following questions about the exception in your notes:

   • What is the name of the exception?
   • Why did the exception occur?
   • Is this exception a checked or an unchecked exception? How can you tell?

5. There are multiple ways to fix the run-time exception that you encountered in the last step. Fix the problem in such a way that the following criteria are met whenever the exception occurs:

   • The program does not crash.
   • The exception message is stil displayed to standard error. To do this, you will need to call the toString() method on the exception object reference given in the catch statement.

   When displaying the exception message, something like the following will suffice (replacing <message> with the actual exception message):

   MyCat: <message>
   

6. From the cs1302-ce04 directory, run the MyCat program with no command-line arguments. What's the difference between this execution of the program and the one performed two steps earlier?

1. Now, let's add some more functionality to the MyCat program. Change the code so that one or more command-line arguments are accepted. The expected behavor is that MyCat should print the files, in order, to standard output, effectively concatenating the contents of the supplied files.

2. From the cs1302-ce04 directory, use your enhanced MyCat program to display the contents of the following three files all passed in at once:Printer.java, standard input ("-"), and MyCat.java in that order! If your program does not currently allow "-" to be specified for arbitrary file names in the list of command-line arguments, then modify it to accomodate that feature.

3. Run your enhanced MyCat program by passing in two filenames as command-line arguments. Make sure the first file does not exist in the file system. Your program should catch the FileNotFoundException, print the appropriate message, and still print the contents of the second file (assuming it exists).

4. Update the comments in the source code to reflect any functionality that has been added since the beginning of this exercise.

Each student needs to individually submit their own work.

1. Create a plain text file called SUBMISSION.md directly inside the cs1302-ce04 directory with the following information:

   1. Your name and UGA ID number; and
   2. Collaborator names, if any.

   Here is an example of the contents of SUBMISSION.md.

   1. Sally Smith (811-000-999)
   2. Collaborators: Joe Allen, Stacie Mack
   

2. Change directories to the parent of cs1302-ce04 (e.g., cd .. from cs1302-ce04). If you would like to make a backup tar file, the instructions are in the submissions steps for ce02. We won't repeat those steps here and you can view them as optional.

3. Use the submit command to submit this exercise to csci-1302:

   $ submit cs1302-ce04 csci-1302
   

   Read the output of the submit command very carefully. If there is an error while submitting, then it will displayed in that output. Additionally, if successful, the submit command creates a new receipt file in the directory you submitted. The receipt file begins with rec and contains a detailed list of all files that were successfully submitted. Look through the contents of the rec file and always remember to keep that file in case there is an issue with your submission.

   Note: You must be on Odin to submit.