hi folks JApplet, JFrame implement the JRoot Interface and therefore Jrootpane is the child of JApplet and JFrame. this actually disallows us to directly add anything to the JAPPlet or Jframe we get a reference of the Jrootpane inside the Jframe or Japplet and add any widget/text components to Jrootpane. in swing what is the advantage behind this concept of having a jrootpane inside a a JApplet or Jframe .
Code simplicity. Why rewrite a piece of code to handle the displaying of components for JFrame, when you can use the same code you used for JApplet. And then you could use it somewhere else as well if you chose to. It is part of the whole object oriented thing.