Applets

Class Applet [ java.applet ]

• This is the base class from which all applets are derived.

• public void init()
• Is used to initialized the Applet.
• It is invoked only once.
• public void start()
• Is invoked when Applet scrolls into View or Restored.
• It is used to start the Applet.
• public void stop()
• Is used to stop the Applet.
• It is invoked when Applet scrolls out of view or browser is minimized.
• public void destroy()
• Is used to destroy the Applet.
• It is invoked only once.
• public void paint(Graphics g)
• is used to paint the Applet. It provides Graphics class object that can be used for drawing oval, rectangle, arc etc.

• public void showStatus( String msg)
• Will display msg into applet containers status bar
• public URL getCodeBase()
• Gets the base URL.
• This is the URL of the directory which contains this applet.
• public URL getDocumentBase()
• Gets the URL of the document in which this applet is embedded.
• public String getParameter(String name)
• Returns the value of the named parameter.
• public Image getImage(URL url)
• Returns an Image object that can then be painted on the screen.
• public void play(URL url)
• Plays the audio clip at the specified URL.

Class Applet Hierarchy

 import java.applet.*;
 import java.awt.*;
 public class MyApplet extends Applet
 {
    String s="";
    public void destroy() 
    {
        s=s+"destroy ";
        showStatus(s);
    }
    public void paint(Graphics g)
    {
        s=s+"paint "; 
        showStatus(s);
    }
    public void stop()
    {
        s=s+"stop ";
        showStatus(s);
    }
    public void start()
    {
        s=s+"start ";
        showStatus(s);
    }
    public void init()
    {
        s=s+"init ";
        showStatus(s);
    }
 }
//<applet code=MyApplet width=300 height=300 ></applet>

• Applet is an old technology.
• In old days they were supported by browsers.
• Now browsers have stopped supporting Applets.
• But still we can test our Applet by using a tool AppletViewer.
• This tool was available till jdk1.8.

AppletViewer

• It is a tool generally used by developers for testing their applets before deploying them to a website.
• It loads the applet class specified in applet tag of the file and calls applet different life cycle methods of applet on different events.