CS 113 - Computer Science 1

Lab 1

Getting Started

In this lab you will:

Confirm lab access
Confirm your ability to log into the lab computers
Set up your account
Create a Java program in Visual Studio Code (VSC)
Compile and run the program from the command line
Compile and run the program from withing VSC

Lab Access

Check that your ID card opens the door into the lab. If it does not, let me know.

Logging In

Find an available computer in the lab. Follow along with me to log in to your Unix account. This process is also described here.
If you cannot log in, let me know.

Terminals

Open a terminal. Follow along with me to log in to your Unix account. This process is also described here.

Directory setup and some Unix

Suppose your user name is Xena. Then your "home directory" is /home/xena. You can see this using the Unix pwd command as follows:

    xena@loin ~$> pwd
    /home/xena

Here the xena@loin ~$> is the Unix "prompt" which shows that you are logged in as "xena" on a machine named "loin". (Your machine name will differ.) The response to the pwd command is /home/xena which is your home directory. pwd is short for "present working directory".

Now make a new subdirectory for all of your work in this course. Call this directory "CS113". (I usually use capital letters to start directory names. This is not required, it is just convenient.) To do so, use the Unix mkdir command as shown

    xena@loin ~$> mkdir CS113

Suggestion, never put spaces into either directory or file names. They are a pain in Unix and in Java.

You can see this is successful by getting a listing of the contents of the current directory using the Unix ls command as follows.

    xena@loin:~$ ls
CS113	 Documents  local  mpub		 Music	Pictures  public_html  tmp
Desktop  Downloads  mail   mpublic_html  Node	Public	  Templates    Videos

ls is short for "list". What you see will be slightly different, but you should certainly see CS113

Now go into the CS113 directory and make a new directory there to hold things you will do today. Then switch into the directory you just made

        xena@loin:~$ cd CS113
        xena@loin:~/CS113$ mkdir Lab01
        xena@loin:~/CS113$ cd Lab01
        xena@loin:~/CS113/Lab01$ ls
        xena@loin:~/CS113/Lab01$ pwd
        /home/xena/CS113/Lab01
        xena@loin:~/CS113$ cd
        xena@loin:~/CS113/Lab01$ pwd
        /home/xena/
        xena@loin:~/CS113$ cd CS113/Lab01
        xena@loin:~/CS113/Lab01$ pwd
        /home/xena/CS113/Lab01

cd is short for "change directory". It is almost always a good idea to use ls after cd to look at the files in the place you just moved to. In this case there are none, which is as expected since you just created the directory.

For each homework and lab, you should do something like the above to create a new clean place for the work you are about to do. That is, create a HW01 directory, a LAB02 directory, etc.

Now lets do something using Visual Studio Code (VSC).

Leave the terminal open, we will return to it

A Program in VSC

Start VSC. You can do this either from the terminal by entering code or from the dots gird in the lower left (as you did for starting a terminal).

Within VSC, select File Menu / "Open Folder"; then navigate to the Lab01 directory you just created and open that folder. Hint, always select the exact folder you want, not one of its parents.

On the left, click on the extensions button (3 squares together and one slightly apart (usually at the bottom)) and confirm in the list of installed extensions that "Extension Pack for Java" is installed.

On the left, click of the top icon -- a document on top of a document.

Put the mouse over "CS113". Just to the right you should get a set of icons. Click on the leftmost -- a document with a plus in the lower left.

Just below a box should appear with a blinking cursor waiting for you to type. Enter "HelloWorld.java" then hit return

Now on the right, start entering the hello world program given below

        public class HelloWorld {
            public static void main(String[] args) {
                System.out.println("Hello World");
            }
        }

Compile and run

Go back to the terminal. Enter the following:

xena@loin:~/CS113/Lab01$ ls
HelloWorld.java
xena@loin:~/CS113/Lab01$ javac HelloWorld.java
xena@loin:~/CS113/Lab01$ ls
HelloWorld.class  HelloWorld.java
xena@loin:~/CS113/Lab01$ java HelloWorld
Hello World

Note that the program you wrote in VSC shows up in the terminal. The we compile the file using the javac command. If successful, this creates a new file "HelloWorld.class". Finally, we run the program using the java command.

Back in VSC

VSC is an IDE (integrated development environment). It would not be particularly integrated if you had to go to a separate terminal to run you program. There are three alternatives.

Open a terminal inside VSC and do the javac/java thing there. To open a terminal in VSC, select "Menu Terminal / New Terminal". This terminal has the same behavior as the terminal you opened earlier.
Just above the "main" function are the words "Run" and "debug" (for me they are light grey). Click on "run" or "debug". This can fail sometimes when the compile and run in the terminal works.
Up near the top of the VSC window there is an arrow pointing right. Click on it to compile and run your program. This can fail sometimes when the compile and run in the terminal works.

Once your Hello World program works, modify it to print "hello world" at least 5 times.

Unix Recap

In this lab you used the following Unix commands. All of these commands also work in Terminal windows on Macs. Most of them work in Command windows (or powershell) on Windows. More next week.

Command	Description
cd	When used with no arguments (as here), return to the home directory
cd xxxx	Switch from the current directory to a subdirectory named xxxx.
cd ..	(This is literally "cd" followed by a space then 2 periods.) Switch from the current directory to the parent of the current directory.
cd xxx/yyy	switch from the current directory to the subdirectory yyy which is contained in the the directory xxx. xxx must be a subdirectory of the current directory
ls	LIst the contents of the current directory
pwd	Show the full path of the current directory
javac Xxx.java	Compile the java program Xxx.java (Xxx.java must be in the current directory
javac Xxx	Run the java program Xxx. The file Xxx.class must be in the current directory. Do not include ".class" -- that is "java Xxx.class" will not work.

What to hand in

Send use your phone to take a picture of yourself with the VSC screen in the background with your final hello world program. Send the picture to gtowell@brynmawr.edu