Applet restrictions

Bruce Eckel's Thinking in Java Contents | Prev | Next

3) Dialog boxes are “untrusted.” In Java, dialog boxes present a bit of a quandary. First of all, they’re not exactly disallowed in applets but they’re heavily discouraged. If you pop up a dialog box from within an applet you’ll get an “untrusted applet” message attached to that dialog. This is because, in theory, it would be possible to fool the user into thinking that they’re dealing with a regular native application and to get them to type in their credit card number, which then goes across the Web. After seeing the kinds of GUIs that the AWT produces you might have a hard time believing anybody could be fooled that way. But an applet is always attached to a Web page and visible within your Web browser, while a dialog box is detached so in theory it could be possible. As a result it will be rare to see an applet that uses a dialog box.

  • Applets take longer to download since you must download the whole thing every time, including a separate server hit for each different class. Your browser can cache the applet, but there are no guarantees. One improvement in Java 1.

Applet advantages

  • There is no installation issue. An applet has true platform independence (including the ability to easily play audio files, etc.) so you don’t need to make any changes in your code for different platforms nor does anyone have to perform any “tweaking” upon installation. In fact, installation is automatic every time the user loads the Web page along with the applets, so updates happen silently and automatically. In traditional client/server systems, building and installing a new version of the client software is often a nightmare.
  • Because of the security built into the core Java language and the applet structure, you don’t have to worry about bad code causing damage to someone’s system. This, along with the previous point, makes Java (as well as alternative client-side Web programming tools like JavaScript and VBScript) popular for so-called


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