Exercise 1: Running a Java Program

Please do this exercise in a group with other students.

Go through the questions and discuss the answers within your group. Write them down/remember them to share later with the class.

Precondition

You should have opened the codeboard.io website and created a new Java codeboard (do not yet change things).

You can fine the setup instructions here

Goal of this exercise is to get an understanding of

what things do you actually need do to write and run a Java program (the ingredients)
what actually needs to happen so that a Java program can run?

Try to find the answers within your group (in case of questions/problems => ask one of your teachers!)

What do you think the program will do?

If you have an idea, explain why!

Now run the program - does it do the thing you have expected?

Take another look at your opened Java project.

You can see that it consists of three major parts.

What is the purpose of each part?

What does each contain and what can you do with it?

How are they connected with each other?

Run the program again.

Observe closely what happens.

How many steps do you observe while running your program?

Do you have an idea, what each step is doing?

We saw the following three parts when opening a new project

on the left a folder with our source code file, Main.java
in the middle our code editor: it showed the content of Main.java and we can edit it there
on the right, a console: as soon as we press the Run button we see some text output related to running our Java program

As soon as we ran our program, we saw three things printed out in the console:

> javac -classpath .:/run_dir/junit-4.12.jar -d . Main.java
> java -classpath .:/run_dir/junit-4.12.jar Main
Hello world!

Given our observations, we learned

Please also check our glossary for terms that are unfamiliar or new to you!

We need a file in that we can save our code. This is called our Source Code File. For Java, such a file always needs to have the file ending .java, e.g. Main.java
We need an editor to open our source code file and make changes. You could use any text editor for this (as a Java source code file is just text) but normally you want to use an editor that is specialized for programming in Java (you will see later when this course progresses what such an editor can do for you)
We need a console where we can run the necessary commands to run our program and see its output.
We need of course the specific commands javac and java available on our computer.

Luckily, when using a tool like codeboard.io, all these things are already given to you, the only thing you need is Internet access.

The following image shows a simple overview of the steps from our source code file to our program actually running:

compile and run java