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Applet.javaAPI DocJava SE 5 API18762Fri Aug 26 14:56:42 BST 2005java.applet

Applet

public class Applet extends Panel
An applet is a small program that is intended not to be run on its own, but rather to be embedded inside another application.

The Applet class must be the superclass of any applet that is to be embedded in a Web page or viewed by the Java Applet Viewer. The Applet class provides a standard interface between applets and their environment.

author
Arthur van Hoff
author
Chris Warth
version
1.77, 06/22/04
since
JDK1.0

Fields Summary
private transient AppletStub
stub
Applets can be serialized but the following conventions MUST be followed: Before Serialization: An applet must be in STOPPED state. After Deserialization: The applet will be restored in STOPPED state (and most clients will likely move it into RUNNING state). The stub field will be restored by the reader.
private static final long
serialVersionUID
AccessibleContext
accessibleContext
Constructors Summary
public Applet()
Creates a new Applet object

exception
HeadlessException if GraphicsEnvironment.isHeadless() returns true.
see
java.awt.GraphicsEnvironment#isHeadless
since
1.4

        if (GraphicsEnvironment.isHeadless()) {
            throw new HeadlessException();
        }
    
Methods Summary
public voiddestroy()
Called by the browser or applet viewer to inform this applet that it is being reclaimed and that it should destroy any resources that it has allocated. The stop method will always be called before destroy.

A subclass of Applet should override this method if it has any operation that it wants to perform before it is destroyed. For example, an applet with threads would use the init method to create the threads and the destroy method to kill them.

The implementation of this method provided by the Applet class does nothing.

see
java.applet.Applet#init()
see
java.applet.Applet#start()
see
java.applet.Applet#stop()

    
public javax.accessibility.AccessibleContextgetAccessibleContext()
Gets the AccessibleContext associated with this Applet. For applets, the AccessibleContext takes the form of an AccessibleApplet. A new AccessibleApplet instance is created if necessary.

return
an AccessibleApplet that serves as the AccessibleContext of this Applet


                                                         
       
        if (accessibleContext == null) {
            accessibleContext = new AccessibleApplet();
        }
        return accessibleContext;
    
public java.applet.AppletContextgetAppletContext()
Determines this applet's context, which allows the applet to query and affect the environment in which it runs.

This environment of an applet represents the document that contains the applet.

return
the applet's context.

	return stub.getAppletContext();
    
public java.lang.StringgetAppletInfo()
Returns information about this applet. An applet should override this method to return a String containing information about the author, version, and copyright of the applet.

The implementation of this method provided by the Applet class returns null.

return
a string containing information about the author, version, and copyright of the applet.

	return null;
    
public java.applet.AudioClipgetAudioClip(java.net.URL url)
Returns the AudioClip object specified by the URL argument.

This method always returns immediately, whether or not the audio clip exists. When this applet attempts to play the audio clip, the data will be loaded.

param
url an absolute URL giving the location of the audio clip.
return
the audio clip at the specified URL.
see
java.applet.AudioClip

	return getAppletContext().getAudioClip(url);
    
public java.applet.AudioClipgetAudioClip(java.net.URL url, java.lang.String name)
Returns the AudioClip object specified by the URL and name arguments.

This method always returns immediately, whether or not the audio clip exists. When this applet attempts to play the audio clip, the data will be loaded.

param
url an absolute URL giving the base location of the audio clip.
param
name the location of the audio clip, relative to the url argument.
return
the audio clip at the specified URL.
see
java.applet.AudioClip

	try {
	    return getAudioClip(new URL(url, name));
	} catch (MalformedURLException e) {
	    return null;
	}
    
public java.net.URLgetCodeBase()
Gets the base URL. This is the URL of the directory which contains this applet.

return
the base {@link java.net.URL} of the directory which contains this applet.
see
java.applet.Applet#getDocumentBase()

	return stub.getCodeBase();
    
public java.net.URLgetDocumentBase()
Gets the URL of the document in which this applet is embedded. For example, suppose an applet is contained within the document:
http://java.sun.com/products/jdk/1.2/index.html
The document base is:
http://java.sun.com/products/jdk/1.2/index.html

return
the {@link java.net.URL} of the document that contains this applet.
see
java.applet.Applet#getCodeBase()

	return stub.getDocumentBase();
    
public java.awt.ImagegetImage(java.net.URL url)
Returns an Image object that can then be painted on the screen. The url that is passed as an argument must specify an absolute URL.

This method always returns immediately, whether or not the image exists. When this applet attempts to draw the image on the screen, the data will be loaded. The graphics primitives that draw the image will incrementally paint on the screen.

param
url an absolute URL giving the location of the image.
return
the image at the specified URL.
see
java.awt.Image

	return getAppletContext().getImage(url);
    
public java.awt.ImagegetImage(java.net.URL url, java.lang.String name)
Returns an Image object that can then be painted on the screen. The url argument must specify an absolute URL. The name argument is a specifier that is relative to the url argument.

This method always returns immediately, whether or not the image exists. When this applet attempts to draw the image on the screen, the data will be loaded. The graphics primitives that draw the image will incrementally paint on the screen.

param
url an absolute URL giving the base location of the image.
param
name the location of the image, relative to the url argument.
return
the image at the specified URL.
see
java.awt.Image

	try {
	    return getImage(new URL(url, name));
	} catch (MalformedURLException e) {
	    return null;
	}
    
public java.util.LocalegetLocale()
Gets the Locale for the applet, if it has been set. If no Locale has been set, then the default Locale is returned.

return
the Locale for the applet
since
JDK1.1

      Locale locale = super.getLocale();
      if (locale == null) {
	return Locale.getDefault();
      }
      return locale;
    
public java.lang.StringgetParameter(java.lang.String name)
Returns the value of the named parameter in the HTML tag. For example, if this applet is specified as
<applet code="Clock" width=50 height=50>
<param name=Color value="blue">
</applet>

then a call to getParameter("Color") returns the value "blue".

The name argument is case insensitive.

param
name a parameter name.
return
the value of the named parameter, or null if not set.

	 return stub.getParameter(name);
     
public java.lang.String[][]getParameterInfo()
Returns information about the parameters that are understood by this applet. An applet should override this method to return an array of Strings describing these parameters.

Each element of the array should be a set of three Strings containing the name, the type, and a description. For example:

String pinfo[][] = {
{"fps", "1-10", "frames per second"},
{"repeat", "boolean", "repeat image loop"},
{"imgs", "url", "images directory"}
};

The implementation of this method provided by the Applet class returns null.

return
an array describing the parameters this applet looks for.

	return null;
    
public voidinit()
Called by the browser or applet viewer to inform this applet that it has been loaded into the system. It is always called before the first time that the start method is called.

A subclass of Applet should override this method if it has initialization to perform. For example, an applet with threads would use the init method to create the threads and the destroy method to kill them.

The implementation of this method provided by the Applet class does nothing.

see
java.applet.Applet#destroy()
see
java.applet.Applet#start()
see
java.applet.Applet#stop()

    
public booleanisActive()
Determines if this applet is active. An applet is marked active just before its start method is called. It becomes inactive just before its stop method is called.

return
true if the applet is active; false otherwise.
see
java.applet.Applet#start()
see
java.applet.Applet#stop()

	if (stub != null) {
	    return stub.isActive();
	} else {	// If stub field not filled in, applet never active
	    return false;
	}
    
public static final java.applet.AudioClipnewAudioClip(java.net.URL url)
Get an audio clip from the given URL.

param
url points to the audio clip
return
the audio clip at the specified URL.
since
1.2

        return new sun.applet.AppletAudioClip(url);
    
public voidplay(java.net.URL url)
Plays the audio clip at the specified absolute URL. Nothing happens if the audio clip cannot be found.

param
url an absolute URL giving the location of the audio clip.

	AudioClip clip = getAudioClip(url);
	if (clip != null) {
	    clip.play();
	}
    
public voidplay(java.net.URL url, java.lang.String name)
Plays the audio clip given the URL and a specifier that is relative to it. Nothing happens if the audio clip cannot be found.

param
url an absolute URL giving the base location of the audio clip.
param
name the location of the audio clip, relative to the url argument.

	AudioClip clip = getAudioClip(url, name);
	if (clip != null) {
	    clip.play();
	}
    
private voidreadObject(java.io.ObjectInputStream s)
Read an applet from an object input stream.

exception
HeadlessException if GraphicsEnvironment.isHeadless() returns true
serial
see
java.awt.GraphicsEnvironment#isHeadless
since
1.4


                            
       
            
        if (GraphicsEnvironment.isHeadless()) {
            throw new HeadlessException();
        }
        s.defaultReadObject();
    
public voidresize(java.awt.Dimension d)
Requests that this applet be resized.

param
d an object giving the new width and height.

	resize(d.width, d.height);
    
public voidresize(int width, int height)
Requests that this applet be resized.

param
width the new requested width for the applet.
param
height the new requested height for the applet.

	Dimension d = size();
	if ((d.width != width) || (d.height != height)) {
	    super.resize(width, height);
	    if (stub != null) {
		stub.appletResize(width, height);
	    }
	}
    
public final voidsetStub(java.applet.AppletStub stub)
Sets this applet's stub. This is done automatically by the system.

If there is a security manager, its checkPermission method is called with the AWTPermission("setAppletStub") permission if a stub has already been set.

param
stub the new stub.
exception
SecurityException if the caller cannot set the stub

	if (this.stub != null) {
	    SecurityManager s = System.getSecurityManager();
	    if (s != null) {
	        s.checkPermission(new AWTPermission("setAppletStub"));
	    }
	}
	this.stub = (AppletStub)stub;
    
public voidshowStatus(java.lang.String msg)
Requests that the argument string be displayed in the "status window". Many browsers and applet viewers provide such a window, where the application can inform users of its current state.

param
msg a string to display in the status window.

	getAppletContext().showStatus(msg);
    
public voidstart()
Called by the browser or applet viewer to inform this applet that it should start its execution. It is called after the init method and each time the applet is revisited in a Web page.

A subclass of Applet should override this method if it has any operation that it wants to perform each time the Web page containing it is visited. For example, an applet with animation might want to use the start method to resume animation, and the stop method to suspend the animation.

Note: some methods, such as getLocationOnScreen, can only provide meaningful results if the applet is showing. Because isShowing returns false when the applet's start is first called, methods requiring isShowing to return true should be called from a ComponentListener.

The implementation of this method provided by the Applet class does nothing.

see
java.applet.Applet#destroy()
see
java.applet.Applet#init()
see
java.applet.Applet#stop()
see
java.awt.Component#isShowing()
see
java.awt.event.ComponentListener#componentShown(java.awt.event.ComponentEvent)

    
public voidstop()
Called by the browser or applet viewer to inform this applet that it should stop its execution. It is called when the Web page that contains this applet has been replaced by another page, and also just before the applet is to be destroyed.

A subclass of Applet should override this method if it has any operation that it wants to perform each time the Web page containing it is no longer visible. For example, an applet with animation might want to use the start method to resume animation, and the stop method to suspend the animation.

The implementation of this method provided by the Applet class does nothing.

see
java.applet.Applet#destroy()
see
java.applet.Applet#init()