What Applet can't do for you
First, it can't run under browser with Java Development Kit version below 1.17. You can detect it as follows. If you have visited any page listedhere and you didn't see anything, enable Java console in your browser and start your attempt again. If you fail again, look into Java console output. Likely, you will see some exceptions indicating that Java Virtual Machine failed to find some methods in the classes. If so, you need to upgrade your browser.
Second, it can't save your work for you if it have data loaded from plain text file on the web. In this case, you can browse the world, make any changes in it but all your changes will be lost as soon as you close Applet. You will not be able to click on Post button to save your changes unless Applet data are loaded from Servlet. You can read more about this onanother page.
Third, because of JDK version restrictions, you can't deal with transparent objects in 3D Views (with Camera Projector). You still can assign transparent colors to objects, but they will not be transparent in the View - you will not notice any transparency.
Fourth, Applet can not directly communicate with more than one other application (the web server it is loaded from or Servlet on the same server). That is, you can not do anything with peer-to-peer data distribution while running Applet.
(C) Copyright 1988-1998,2001 Anton Kolonin
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