Project Setup: Lesson 2: Running the Code #

Warning: Work in Progress
We are still working to improve this page before releasing it to students. It may change considerably before first release.

The main function #

Any non-trivial program will be made up of many functions and so we need a way that we can specify which function is meant to be called whenever the program starts up. For example, I can write a function that prints “hello” to the screen, but I need to decide when to call that function.

This is what I would use the “main” function of a program to do. Lets say on program start, I print “Hello” to the screen, wait 5 seconds and then print “goodbye” and exit the program. In clojure this would look like the below

    (ns trivialprogram.core) 

    (defn PrintHello [] (println "Hello!")) 

    (defn PrintGoodbye [] (println "Goodbye!))

    (defn -main [] 

    (PrintHello) 

    (Thread/sleep 5000) 

    (PrintGoodbye) 

    ) 

Notice the (Thread/sleep 5000)

5000 milliseconds = 5 seconds

The slash indicates that sleep is a function in the clojure Thread library. This leads us into our next topic

Libraries #

Probably write this into

Running A Program #

The important thing to understand about using java however is that any code that we write will get compiled into a .jar file which is a file designed to run on the java operating system. To run it on windows or any of the above operating systems we have to specify that we need to use java to run the program

java -jar CompiledFile.jar

Fortunately this command is the same regardless of whether you are running on Windows, Mac, or Linux. Mobile operating systems are slightly different but the concept of how the program is run is the same.

Now that we know what a source code file is we can talk about what the format must be in order for our compiler to read the text that we write and turn it into a computer program

Running a Compiled Jar File #

If we want to run a jar file we simply tell the computer terminal to run the java file and the program will start

java -jar CompiledFile.jar