Module 0: Your First Program

• (Windows users: we recommend using Gitbash and following similar steps)

• What editing looks like this in the pico editor:

  

• What compiling looks like on the Terminal:
  (You type only the javac HelloWorld.java part. The Desktop$ part is written by the Terminal and could look different on your laptop)

  

• What execution looks like on the Terminal:
  (Again, you type only the java HelloWorld part.)

  

• (Windows users: a parallel set of instructions can be found on the Gitbash page.)

• Step 1: launch a Terminal window by searching for Terminal

  

  after which you type "terminal"

  

  which should launch a Terminal window that looks something like this (not exactly the same on every Mac):

  

  Note:

  • If the above approach did not find the Terminal, you may need to open Finder, then navigate to Applications, then to Utilities, as shown here and double-click on Terminal to launch it.
  • Your Terminal may look a little different, for example, it may look like this or like this, or something else. That's OK.
  
  

• Step 2: enter the pico (or nano, on some laptops) editor by typing pico HelloWorld.java (followed by hitting the Return-key or Enter-key) in the Terminal window:

  

  which brings up the editor and a blank workspace:

  

  Note: if your computer does not have pico installed, you may have to use a variation called nano. In this case, you'll type nano HelloWorld.java (and use nano henceforth).

• Step 3: type in the program exactly as shown here, paying close attention to spacing:

  

  A note about pico (or nano):

  • This is a very basic editor.
  • You'll notice that the mouse won't work in the editor.
  • Instead, use the up-down-left-right arrows to move around in the text.
  • pico also uses many "control" commands (where you press "control" and a keyboard key simultaneously).
  
  

• Step 4: save the program by typing ctrl-x inside pico.
         ⇒ ctrl-x means "press the control key and x key together"
  This will prompt you as follows (where you need to type y):

  

  After which you will see

  

  where you need to hit the Enter/Return key. This brings you to

  

• Step 5: compile the program by typing javac HelloWorld.java (followed by Enter/Return, which we will assume you will do for such commands in the future).

  

  What if the javac part did not work? You might see something in the Terminal that looks like: -bash: javac: command not found
  Then, use these instructions to install Java

• Step 6: execute the program by typing java HelloWorld in the Terminal.

• What did you see?

• You should see something like this (a screenshot that we've annotated)

• Note for Windows users: a parallel set of instructions can be found on the Gitbash page.

Thus, you have just solved this exercise:

0.1 Exercise: Write a program to print "Hello World!" to the screen.

0.2 Video: