applet.java

applet 小程序 提供给大家学习参考

/*
 * @(#)Applet.java	1.77 04/06/22
 *
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
package java.applet;

import java.awt.*;
import java.awt.image.ColorModel;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.net.URL;
import java.net.MalformedURLException;
import java.util.Hashtable;
import java.util.Locale;
import javax.accessibility.*;

/**
 * An applet is a small program that is intended not to be run on
 * its own, but rather to be embedded inside another application.
 * <p>
 * The <code>Applet</code> 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 <code>Applet</code> 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
 */
public class Applet extends Panel {
    
    /**
     * Creates a new Applet object
     * @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
     * <code>GraphicsEnvironment.isHeadless()</code> returns
     * <code>true</code>
     * @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.
     * <p>If there is a security manager, its <code> checkPermission </code>
     * method is called with the
     * <code>AWTPermission("setAppletStub")</code>
     * 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 <code>start</code> method is called. It becomes
     * inactive just before its <code>stop</code> method is called.
     *
     * @return  <code>true</code> if the applet is active;
     *          <code>false</code> 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:
     * <blockquote><pre>
     *    http://java.sun.com/products/jdk/1.2/index.html
     * </pre></blockquote>
     * The document base is:
     * <blockquote><pre>
     *    http://java.sun.com/products/jdk/1.2/index.html
     * </pre></blockquote>
     *
     * @return  the {@link java.net.URL} of the document that contains this
     *          applet.
     * @see     java.applet.Applet#getCodeBase()
     */
    public URL getDocumentBase() {
	return stub.getDocumentBase();
    }

    /**
     * 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()
     */
    public URL getCodeBase() {
	return stub.getCodeBase();
    }

    /**
     * Returns the value of the named parameter in the HTML tag. For
     * example, if this applet is specified as
     * <blockquote><pre>
     * &lt;applet code="Clock" width=50 height=50&gt;
     * &lt;param name=Color value="blue"&gt;
     * &lt;/applet&gt;
     * </pre></blockquote>
     * <p>
     * then a call to <code>getParameter("Color")</code> returns the
     * value <code>"blue"</code>.
     * <p>
     * The <code>name</code> argument is case insensitive.
     *
     * @param   name   a parameter name.
     * @return  the value of the named parameter,
     *          or <code>null</code> 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.
     * <p>
     * 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);
    }

    /**
     * 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 <code>Image</code> object that can then be painted on
     * the screen. The <code>url</code> that is passed as an argument
     * must specify an absolute URL.
     * <p>
     * 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 <code>Image</code> object that can then be painted on
     * the screen. The <code>url</code> argument must specify an absolute
     * URL. The <code>name</code> argument is a specifier that is
     * relative to the <code>url</code> argument.
     * <p>
     * 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
     *                 <code>url</code> 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 <code>AudioClip</code> object specified by the