day 20

the java cup is half full 2: an applet a day

The Java craze is just one of several crazes which are a part of the daily Internet hysteria. "Plug-ins" and "agents" are others, and I will have more to say about them in later Daily Doses. The thrust of the Java craze is the so-called applet. An applet is a handler that responds to some event created by the user when viewing an HTML document through a browser like Navigator. Typical events are a press of a keyboard, a mouse click on a region of the screen, or a change in a variable. Here is how a Java applet works. A skeletal structure called AWT (Another Windowing Toolkit, or Abstract Windowing Toolkit) hiding underneath the Navigator browser intercepts all user interactions. That is, AWT catches mouse-down events, keyboard events, etc., and passes them on to a handler. Each handler carries out the desired work. One handler might animate a bouncing ball, another might wait for the user to enter text into a field in a form, and yet another might generate a sound when the user clicks on a GUI button. Handlers are simply procedures that are called whenever needed. Suppose the AWT intercepts an event and then passes control to the appropriate event handler. Further suppose the handler is written in Java. Lets take this one step further. Suppose Java procedures for all handlers are embedded in the HTML-formatted document being viewed by a browser. The event passes to the AWT code, then the event handler, and finally to the Java code that implements the appropriate action. When the Java code executes, the bouncing ball bounces, and the animation animates. This is the idea of an applet. It is not necessary to write all applets in Java. Only the public relations department of JavaSoft thinks that all applets must be written in Java. In fact, the Java vultures are waiting in the wings - when Java slips, they plan to swoop down and pick its bones. Tomorrow we expose these carrion eaters for what they are.

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