hw01 Command Line Compilation and Packages

This homework assignment is designed to provide further practice with command-line text editors as well as compiling Java code organized into packages on a Unix system.

Prerequisite Knowledge

• Emacs Chapter
• Package Chapter

Course-Specific Learning Outcomes

• LO1.a: Navigate and modify files, directories, and permissions in a multi-user Unix-like environment.
• LO1.c: Create and modify text files and source code using a powerful terminal-based text editor such as Emacs or Vi.
• LO1.d: (Partial) Use shell commands to compile new and existing software solutions that are organized into multi-level packages and have external dependencies.

Questions

In your notes, answer the questions in the following exercise steps. All instructions assume that you are logged into the Odin server.

NOTE: For each step, please provide in your notes the full command that you typed to make the related action happen along with an explanation of why that command worked. Some commands require multiple options. It is important to not only recall what you typed but also why you typed each of them. You won't need to submit your notes in your final submission. However, if done properly, your exercise notes will serve as a helpful study guide for the exam.

Exercise Steps

Checkpoint 1 Steps

1. In your home directory on Odin create the subdirectory structure seen below. What single command can be used to create all of these directories at once?

   homework1
    |--- src
          |--- cs1302
                |--- example
   

2. Navigate to the src directory that you just created. In this example, src is the default package directory for source code. Inside the src directory, create a file called Hello.java using either the touch command or using Emacs. Within this file, write a Java program to accomplish the following tasks:

   • prompt the user for their name
   • read in the user's full name
   • output Hello, <user> with their name instead of <user>.

   Remember: Don't forget the class declaration and the main method! On Odin, you have to type these out manually.

3. Compile and run your code directly from the default package for source code (the src directory in this example). Don't use the -d option for javac in this step. In which directory is the compiled code contained?

4. Execute the tree command from inside of your src directory. You should see output similar to this:

   .
   ├── cs1302
   │   └── example
   ├── Hello.class
   └── Hello.java
   

5. This example demonstrates compiling without using a Java package. In the next step, we will use packages to further organize our code. Once you are confident that it is working, delete the compiled (byte) code (the class file - not your source code).

6. Move the Hello.java file (source code) into the cs1302.example package. What two things must be done to accomplish this? Hint: Named Packages

7. For better organization, let's separate the source code from the compiled code. Directly inside the homework1 directory, add a subdirectory called bin. This directory will be the default package for our compiled code. From within homework1, what is the single command to compile Hello.java and place the compiled code into the bin directory? Remember to use tab completion when typing in Unix to avoid mistakes and save you time!

8. From the homework1 directory, what is the single command to run the Hello program?

9. From your home directory (not homework1), what is the single command to run the Hello program?

10. Execute the tree command from directly within your homework1 directory. If the previous steps were executed correctly, you should see the following output:

    Note: If you see any tilda (~) files, those are just backup copies of older versions of your files. You can ignore those.

    .
    ├── bin
    │   └── cs1302
    │       └── example
    │           └── Hello.class
    └── src
        └── cs1302
            └── example
                └── Hello.java
    

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Checkpoint 2 Steps

1. Navigate to the homework1 folder and add a cs1302.utility package directory to your hierarchy. Note: The utility directory will need to be inside of the cs1302 folder. In your notes, write the command to create the utility folder in the proper location without changing out of the homework1 directory.

2. Create a class called MyMethods in the cs1302.utility package. Make sure to type the class declaration. This class won't need a main method because it won't be run directly.

3. Add a single, static method called max to the MyMethods class with the following signature:

   /**
    * Returns the larger of the two input parameters. If the parameters
    * are equal, either value can be returned.
    *
    * @param num1 the first number to check.
    * @param num2 the second number to check.
    * @return the larger of the two parameters.
    */
   public static int max(int num1, int num2) {
      // Your code here
   } // max

4. Implement the body of the max method. The method should determine and return the bigger of two int values supplied as parameters to the method. These values will be supplied when you call the method in a later step. Note: You should not use the Scanner class inside of the MyMethods class.

   PROTIP: Unless it is specifically stated, it is best to always work from the main project directory. For example, while working on the source code for this exercise, you can modify all of the files without leaving the homework1 directory by providing the relative path (using tab completion) to the file from the homework1 directory. This means you would rarely use the cd command while working on an assignment. When Unix beginners overuse the cd command, they often find themselves lost in the directory structure which can lead to mistakes and, in rare cases, frustration!

5. Assuming your present working directory is still homework1, what is the command to compile MyMethods.java and place the byte code in the bin directory? Remember, there are no dependencies when compiling MyMethods.java as it does not depend on any other source code.

   Now that you've compiled both Hello.java and MyMethods.java, look in the bin directory. Notice the directory hierarchy that was automatically created.

6. Now, modify the Hello class in the Hello.java file. Have it print out the maximum of two values input by the user. To accomplish this, in the main method of your Hello class, you should read two integers from a valid Scanner object and pass those values into the max method you created in the MyMethods utility class. In other words, you should call the max method in MyMethods from the main method in your Hello class and print the result.

   Note: You must import MyMethods in Hello.java.

7. What is the command to compile the Hello class from the homework1 directory and place the compiled code into bin? Note: there is now a dependency in Hello.java. It relies on the code from MyMethods, so the compiler needs to know where to find that class.

8. Execute the tree command from directly within your homework1 directory. If the previous steps were executed correctly, you should see the following output:

   Note: If you see any tilde (~) files, those are just backup copies of older versions of your files. You can ignore those.

   .
   ├── bin
   │   └── cs1302
   │       ├── example
   │       │   └── Hello.class
   │       └── utility
   │           └── MyMethods.class
   └── src
       └── cs1302
           ├── example
           │   └── Hello.java
           └── utility
               └── MyMethods.java
   

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Submission Steps

Each student needs to individually submit their own work.

1. Create a plain text file called SUBMISSION.md directly inside the homework1 directory with your name and UGA ID number.

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

   Sally Smith (811-000-999)
   

2. From the parent directory of the homework1 folder, use the submit command to submit this assignment to csci-1302:

   $ submit homework1 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 receipt 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.

If you would like to make a copy of your homework assignment into a single, zipped file, follow the steps below (not required)

1. Change directories to the parent of homework1 (e.g., cd .. from homework1). We will use the tar command to combine our directory hierarchy into a single file for backup purposes. To do this, execute the command:

   $ tar -cf homework1.tar homework1/
   

   Read the manual page for tar in section 1 of the manual to learn more about tar and its various options.

2. List the contents of your directory and make sure you see homework1.tar. Now, to make sure this tar file contains all of the work you just did, list all of its contents with the command:

   $ tar -tf homework1.tar
   

3. Now, to make this file smaller, we will compress it with gzip. Execute the command:

   $ gzip homework1.tar
   

   Read the manual page for gzip in section 1 of the manual to learn more about gzip and its various options.

4. List the contents of your directory and make sure you see homework1.tar.gz instead of homework1.tar. Now, you have a compressed backup of your directory saved in the .tar.gz file.

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Copyright © Michael E. Cotterell, Bradley J. Barnes, and the University of Georgia. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License to students and the public and licensed under a Creative Commons Attribution-NonCommercial 4.0 International License to instructors at institutions of higher education. The content and opinions expressed on this Web page do not necessarily reflect the views of nor are they endorsed by the University of Georgia or the University System of Georgia.