Good Day

I am new to programming and have started a Java course. I have the new Mac book and am using xcode as a IDE.
I have done the code and the program runs as an applet however I cannot change the name of the HTML file to match the applet name. If I do it doesn't run. Also I cannot open the JAR file in applet launcher....

Can anybosy help, I am sure it's just a setting or something.

Regards
Dave