So I'm learning java and I kinda got confused here...
So while learning threads I learned that it is necessary to extend Thread class or implement Runnable class. 
And while going through this program Thread.sleep() is used without doing any of the above process.

link:
<http://www.abihitechsolutions.com/applets-mini-project-in-java-free-source-code/>

Can someone explain me what is going on?