I may not have my terminology right here, plus I'm not at all sure I understood you correctly, but I'll try:
A Java Applet, which would appear in the browser window, wouldn't be affected by the back/forward buttons, but the window itself would. So if you go to x.com, which has a Java applet, from y.com and go from there to z.com, neither of which do, you could press bak on z.com to go to x.com, and back on x.com to go to y.com, and vice-versa with the forward button. The actual content of the applet would be irrelevant, unless it did something to affect the back/forward buttons. I dunno if Java can or not.