The idea is that sometimes homework or lab assignments are posted on a website and you don't hear about it it immediately. The script and associated java class download the html of a webpage, store this code in a file, then compare this file to the previous file (if there is no previous file, then the downloaded file is the first file...) if the file is different, then send out an email to let the User know that the webpage has changed in some way.
In this way I receive an email alert on my phone, letting me know that the webpage has changed. The email also includes the URL of the webpage that changed.
a shell script to execute the code every 30 minutes
Notes: Several aspects of this could be improved. The shell script is particularly clumsy but this turned out to be useful on several occasions. Things that may be added in the future include better file and password management. A GUI and an Android app.