How to make an Applet?

What is applet?

Applet is a java application that is embedded (and is running) in the browser such as Internet Explorer or Netscape. An applet program must extends the Applet class. When you write an applet, it should start like this:

        class Demo extends Applet

And because the Applet class is in the java.applet package, you must also import this package.

        import java.applet.*;
        
        class Demo extends Applet

Methods of applets..

Applet has several methods that are reffered to as milestones. They are called milestones because they indicate an action that happens during the applet's lifecycle. These methods are defined in the Applet class, and when you are writing an applets you may overrides them. Who is actually invokes those methods? The answer is the browser where the applet is running. Or, more accurate, is the application that runs the applets will invokes those milestones methods. The browser is one of this application, and other's can be appletviewer. I don't know any other applications that can run or embed applet inside them.

What are the milestones methods?

These methods are declared in the Applet class as ...

        public void init() { }
        public void start() { }
        public void stop() { }
        public void destroy() { }

When an applet is loaded inside the browser, the init() method is called, then the start() method is called. When you closes the browser window, or leaves the applet page, the stop() method is called. And, before the applet is unloading, the destory() method is called.

All these methods are instance methods. To access these methods, an object of type Applet must be instantiate first. The browser actually does this. It create an instance of the Applet class first, then call the init() method followed by the start() method.