* 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
* @since JDK1.0
*/
public class Applet extends Panel {
/**
* Constructs a new Applet.
*
* Note: Many methods in java.applet.Applet
* may be invoked by the applet only after the applet is
* fully constructed; applet should avoid calling methods
* in java.applet.Applet in the constructor.
*
* @exception HeadlessException if GraphicsEnvironment.isHeadless()
* returns true.
* @see java.awt.GraphicsEnvironment#isHeadless
* @since 1.4
*/
public Applet() throws HeadlessException {
if (GraphicsEnvironment.isHeadless()) {
throw new HeadlessException();
}
}
/**
* 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.
*/
transient private AppletStub stub;
/* version ID for serialized form. */
private static final long serialVersionUID = -5836846270535785031L;
/**
* Read an applet from an object input stream.
* @exception HeadlessException if
* GraphicsEnvironment.isHeadless() returns
* true
* @serial
* @see java.awt.GraphicsEnvironment#isHeadless
* @since 1.4
*/
private void readObject(ObjectInputStream s)
throws ClassNotFoundException, IOException, HeadlessException {
if (GraphicsEnvironment.isHeadless()) {
throw new HeadlessException();
}
s.defaultReadObject();
}
/**
* 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
*/
public final void setStub(AppletStub stub) {
if (this.stub != null) {
SecurityManager s = System.getSecurityManager();
if (s != null) {
s.checkPermission(new AWTPermission("setAppletStub"));
}
}
this.stub = (AppletStub)stub;
}
/**
* 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()
*/
public boolean isActive() {
if (stub != null) {
return stub.isActive();
} else { // If stub field not filled in, applet never active
return false;
}
}
/**
* 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
*
* http://java.sun.com/products/jdk/1.2/index.html
*
* <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.
*/
public String getParameter(String name) {
return stub.getParameter(name);
}
/**
* 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. */ public AppletContext getAppletContext() { return stub.getAppletContext(); } /** * Requests that this applet be resized. * * @param width the new requested width for the applet. * @param height the new requested height for the applet. */ public void resize(int width, int height) { Dimension d = size(); if ((d.width != width) || (d.height != height)) { super.resize(width, height); if (stub != null) { stub.appletResize(width, height); } } } /** * Requests that this applet be resized. * * @param d an object giving the new width and height. */ public void resize(Dimension d) { resize(d.width, d.height); } /** * Indicates if this container is a validate root. *
* {@code Applet} objects are the validate roots, and, therefore, they
* override this method to return {@code true}.
*
* @return {@code true}
* @since 1.7
* @see java.awt.Container#isValidateRoot
*/
@Override
public boolean isValidateRoot() {
return true;
}
/**
* 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.
*/
public void showStatus(String msg) {
getAppletContext().showStatus(msg);
}
/**
* 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
*/
public Image getImage(URL url) {
return getAppletContext().getImage(url);
}
/**
* 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
*/
public Image getImage(URL url, String name) {
try {
return getImage(new URL(url, name));
} catch (MalformedURLException e) {
return null;
}
}
/**
* 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
*/
public final static AudioClip newAudioClip(URL url) {
return new sun.applet.AppletAudioClip(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
*/
public AudioClip getAudioClip(URL url) {
return getAppletContext().getAudioClip(url);
}
/**
* 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
*/
public AudioClip getAudioClip(URL url, String name) {
try {
return getAudioClip(new URL(url, name));
} catch (MalformedURLException e) {
return null;
}
}
/**
* 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.
*/
public String getAppletInfo() {
return null;
}
/**
* Gets the locale of the applet. It allows the applet
* to maintain its own locale separated from the locale
* of the browser or appletviewer.
*
* @return the locale of the applet; if no locale has
* been set, the default locale is returned.
* @since JDK1.1
*/
public Locale getLocale() {
Locale locale = super.getLocale();
if (locale == null) {
return Locale.getDefault();
}
return locale;
}
/**
* 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.
*/
public String[][] getParameterInfo() {
return null;
}
/**
* 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.
*/
public void play(URL url) {
AudioClip clip = getAudioClip(url);
if (clip != null) {
clip.play();
}
}
/**
* 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.
*/
public void play(URL url, String name) {
AudioClip clip = getAudioClip(url, name);
if (clip != null) {
clip.play();
}
}
/**
* 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 void init() {
}
/**
* 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 void start() {
}
/**
* 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()
*/
public void stop() {
}
/**
* 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 void destroy() {
}
//
// Accessibility support
//
AccessibleContext accessibleContext = null;
/**
* 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
* @since 1.3
*/
public AccessibleContext getAccessibleContext() {
if (accessibleContext == null) {
accessibleContext = new AccessibleApplet();
}
return accessibleContext;
}
/**
* This class implements accessibility support for the
* Applet class. It provides an implementation of the
* Java Accessibility API appropriate to applet user-interface elements.
* @since 1.3
*/
protected class AccessibleApplet extends AccessibleAWTPanel {
private static final long serialVersionUID = 8127374778187708896L;
/**
* Get the role of this object.
*
* @return an instance of AccessibleRole describing the role of the
* object
*/
public AccessibleRole getAccessibleRole() {
return AccessibleRole.FRAME;
}
/**
* Get the state of this object.
*
* @return an instance of AccessibleStateSet containing the current
* state set of the object
* @see AccessibleState
*/
public AccessibleStateSet getAccessibleStateSet() {
AccessibleStateSet states = super.getAccessibleStateSet();
states.add(AccessibleState.ACTIVE);
return states;
}
}
}