That's how applet <-> browser handling works ..
http://www.dpunkt.de/java/Programmieren_mit_Java/Applets_und_Applikationen/5.html
http://www.dpunkt.de/java/Programmieren_mit_Java/Applets_und_Applikationen/6.html
http://www.dpunkt.de/java/Programmieren_mit_Java/Applets_und_Applikationen/7.html
http://www.dpunkt.de/java/Programmieren_mit_Java/Applets_und_Applikationen/8.html
Each applet has four methods that determine its life cycle. Calling this method automatically when certain user actions from the browser. These actions include, for example, the loading of an applet or leaving an HTML page in which an applet is embedded. Some of these methods:
init () Is always called when the applet is initialized. This occurs immediately after it is loaded.
start () Is executed after the initialization of an applet. There will also use this method instead of whenever the browser or the applet viewer from the icon display is restored to normal size. With browsers, start () then called up when a page where an applet is located, load times will be repeated on.
stop () Is the counterpart to start () . A call occurs when the browser or the appletviewer reduced to an icon or an HTML page is exited with an embedded applet in a browser.
destroy () Is always called when the applet is destroyed. The destruction occurs, for example, when it is removed from the browser. During a Web session may be downloaded lots of applets. Thus, a large amount of memory available. This reduces the amount of used memory is not constantly increasing, creating, for example, the Netscape Navigator Court, be removed by excessive memory load old applets. If a remote applet loaded again, it goes through the initialization again.
By default, the above methods any code. They can be in an appropriate manner of writing to the functionality required to give his applet. init () is usually implemented with applets, since this procedure store the applet is executed first and after the initialization tasks, such as creating objects, takes over . The other methods can be overridden as required.
To get an idea of how the life cycle methods are called, you can test the following applet:
import java.applet.Applet;
public class demo extends Applet {cycle
public void init () {
System.out.println ("init"
;
}
public void start () {
System.out.println ("start"
;
}
public void stop () {
System.out.println ("stop"
;
}
public void destroy () {
System.out.println ("destroy"
;
}
}
The applet gives each the name of the method that is called by the interpreter, on the standard output, ie either on the console from which the applet viewer is started, the Netscape Communicator, for example, by selecting the menu "Communicator | Java Console or call the Java plug-in by enabling the Java console on the Java icon in the taskbar. Figure 7.1 life cycle methods shows the dependence of the calls by the actions of the user.
Applet and browser to communicate with each other. As a browser communicates with the call of methods of the life cycle of an applet, as demonstrated in the previous section.
An applet also has the ability to communicate with the browser. An applet can:
a new URL in the browser,
the status bar of the browser change,
Message exchange with applets that are on the same HTML page.
This communication is via the interface applet context settled. applet context but not by the applet, but the browser or applet viewer is implemented. applet context of the particular environment is replaced by the one from the class by calling the Applet method provided getAppletContext () .
applet context contains all the methods to communicate with the browser are required to. The individual methods are described in more detail.
Show the data in a URL
An applet has the option of data from a new URL in the browser to load. This can be applied for example to implement a navigator. Another possibility is to implement an image map. In an applet can be status text, depending on mouse position change (see next section) and then pressure in mice, a new URL 's. For this purpose, we use the method show document () of the applet context . showDocument () is available in two versions:
showDocument (URL) Shows the data from the specified URL in the browser.
showDocument (URL, String) Shows the data from the specified URL as the string passed in browser frame. However, this method can be applied only to a browser capable of displaying frames (eg Netscape Navigator). The individual values for string, see the reference.
For example: A browser is to be divided into two frames. A browser frame is used to display the HTML pages that contain information and the second frame contains an applet that is used for navigation.
The applet has two navigation buttons. Each of the buttons representing a HTML page. If you press a button, the page information in the frame is loaded.
Viewing a document introduced by the following two lines:
URL page = new URL (getCodeBase (), "FirstPage.html"
;
getAppletContext () showDocument (page, "data"
;.
The above code is executed when the button is clicked, the page should load SecondPage.html.
First class is a copy of the URL generated. This is necessary because one of the parameters show document () of type URL 's. The class URL is in Section 13.1 explains in detail.
Thereafter, the data of the URL with the method show document () appears. The location and name of the browser frame in which the data will be displayed, passes them as parameters. In this case, "the file FirstPage.html in frame with the name" data is displayed.
