applet.java

《移动Agent技术》一书的所有章节源代码。

/*
 * @(#)Applet.java	1.37 97/01/02
 * 
 * Copyright (c) 1995, 1996 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 * 
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 * 
 * CopyrightVersion 1.1_beta
 * 
 */
package java.applet;

import java.awt.*;
import java.awt.image.ColorModel;
import java.net.URL;
import java.net.MalformedURLException;
import java.util.Hashtable;
import java.util.Locale;

/**
 * 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     1.42, 03/12/97
 * @since       JDK1.0
 */
public class Applet extends Panel {
    /**
     * 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;

    /**
     * Sets this applet's stub. This is done automatically by the system. 
     * 
     * @param   stub   the new stub.
     * @since   JDK1.0
     */
    public final void setStub(AppletStub stub) {
	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 immediately after 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()
     * @since   JDK1.0
     */
    public boolean isActive() {
	if (stub != null) {
	    return stub.isActive();
	} else {	// If stub field not filled in, applet never active
	    return false;
	}
    }
    
    /**
     * Gets the document URL. This is the URL of the document in which
     * the applet is embedded.
     *
     * @return  the <a href="java.net.URL.html#_top_"><code>URL</code></a> of
     *          the document that contains this applet.
     * @see     java.applet.Applet#getCodeBase()
     * @since   JDK1.0
     */
    public URL getDocumentBase() {
	return stub.getDocumentBase();
    }

    /**
     * Gets the base URL. This is the URL of the applet itself. 
     *
     * @return  the <a href="java.net.URL.html#_top_"><code>URL</code></a> of
     *          this applet.
     * @see     java.applet.Applet#getDocumentBase()
     * @since   JDK1.0
     */
    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
     * <ul><code>
     *	&lt;applet code="Clock" width=50 height=50&gt;<br>
     *  &lt;param name=Color value="blue"&gt;<br>
     *  &lt;/applet&gt;
     * </code></ul>
     * <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.
     * @since   JDK1.0
     */
     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.
     * @since   JDK1.0
     */
    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.
     * @since   JDK1.0
     */
    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.
     * @since   JDK1.0
     */    
    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.
     * @since   JDK1.0
     */
    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
     * @since   JDK1.0
     */
    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
     * @since   JDK1.0
     */
    public Image getImage(URL url, String name) {
	try {
	    return getImage(new URL(url, name));
	} catch (MalformedURLException e) {