why can't we instantiate an applet class in java?

Answer 1

You can. It will have a default constructor. All you need to do is put it into another container, such as a JFrame (for JApplet) or Frame (for Applet). Applet is a subclass of Panel and is therefore just another container. Since the browser won't be calling init(), start(), stop(), or destroy(), you will need to do that, e.g. in your constructor, create an instance, add to your container, and then call init() and start() on the applet instance.