libjava/java/applet/Applet.java

   1 /* Applet.java -- Java base applet class
   2    Copyright (C) 1999, 2002 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.applet;
  40
  41 import java.awt.Dimension;
  42 import java.awt.GraphicsEnvironment;
  43 import java.awt.HeadlessException;
  44 import java.awt.Image;
  45 import java.awt.Panel;
  46 import java.io.IOException;
  47 import java.io.ObjectInputStream;
  48 import java.net.MalformedURLException;
  49 import java.net.URL;
  50 import java.util.Locale;
  51 import javax.accessibility.AccessibleContext;
  52 import javax.accessibility.AccessibleRole;
  53 import javax.accessibility.AccessibleState;
  54 import javax.accessibility.AccessibleStateSet;
  55
  56 /**
  57  * This is the base applet class.  An applet is a Java program that
  58  * runs inside a web browser or other applet viewer in a restricted
  59  * environment.
  60  *
  61  * <p>To be useful, a subclass should override at least start(). Also useful
  62  * are init, stop, and destroy for control purposes, and getAppletInfo and
  63  * getParameterInfo for descriptive purposes.
  64  *
  65  * @author Aaron M. Renn <arenn@urbanophile.com>
  66  * @author Eric Blake <ebb9@email.byu.edu>
  67  * @since 1.0
  68  * @status updated to 1.4
  69  */
  70 public class Applet extends Panel
  71 {
  72   /**
  73    * Compatible with JDK 1.0+.
  74    */
  75   private static final long serialVersionUID = -5836846270535785031L;
  76
  77   /** The applet stub for this applet. */
  78   private transient AppletStub stub;
  79
  80   /**
  81    * The accessibility context for this applet.
  82    *
  83    * @serial the accessibleContext for this
  84    * @since 1.2
  85    */
  86   private AccessibleContext accessibleContext;
  87
  88   /**
  89    * Default constructor for subclasses.
  90    *
  91    * @throws HeadlessException if in a headless environment
  92    */
  93   public Applet()
  94   {
  95     if (GraphicsEnvironment.isHeadless())
  96       throw new HeadlessException();
  97   }
  98
  99   /**
 100    * The browser calls this method to set the applet's stub, which is the
 101    * low level interface to the browser. Manually setting this to null is
 102    * asking for problems down the road.
 103    *
 104    * @param stub the applet stub for this applet
 105    */
 106   public final void setStub(AppletStub stub)
 107   {
 108     this.stub = stub;
 109   }
 110
 111   /**
 112    * Tests whether or not this applet is currently active. An applet is active
 113    * just before the browser invokes start(), and becomes inactive just
 114    * before the browser invokes stop().
 115    *
 116    * @return <code>true</code> if this applet is active
 117    */
 118   public boolean isActive()
 119   {
 120     return stub.isActive();
 121   }
 122
 123   /**
 124    * Returns the basename URL of the document this applet is embedded in. This
 125    * is everything up to the final '/'.
 126    *
 127    * @return the URL of the document this applet is embedded in
 128    * @see #getCodeBase()
 129    */
 130   public URL getDocumentBase()
 131   {
 132     return stub.getDocumentBase();
 133   }
 134
 135   /**
 136    * Returns the URL of the code base for this applet.
 137    *
 138    * @return the URL of the code base for this applet
 139    */
 140   public URL getCodeBase()
 141   {
 142     return stub.getCodeBase();
 143   }
 144
 145   /**
 146    * Returns the value of the specified parameter that was specified in
 147    * the <code>&lt;APPLET&gt;</code> tag for this applet.
 148    *
 149    * @param name the parameter name
 150    * @return the parameter value, or null if the parameter does not exist
 151    * @throws NullPointerException if name is null
 152    */
 153   public String getParameter(String name)
 154   {
 155     return stub.getParameter(name);
 156   }
 157
 158   /**
 159    * Returns the applet context for this applet.
 160    *
 161    * @return the applet context for this applet
 162    */
 163   public AppletContext getAppletContext()
 164   {
 165     return stub.getAppletContext();
 166   }
 167
 168   /**
 169    * Requests that the applet window for this applet be resized.
 170    *
 171    * @param width the new width in pixels
 172    * @param height the new height in pixels
 173    */
 174   public void resize(int width, int height)
 175   {
 176     stub.appletResize(width, height);
 177   }
 178
 179   /**
 180    * Requests that the applet window for this applet be resized.
 181    *
 182    * @param dim the requested dimensions
 183    * @throws NullPointerException if dim is null
 184    */
 185   public void resize(Dimension dim)
 186   {
 187     resize(dim.width, dim.height);
 188   }
 189
 190   /**
 191    * Displays the specified message in the status window if that window
 192    * exists.
 193    *
 194    * @param message the status message, may be null
 195    */
 196   public void showStatus(String message)
 197   {
 198     getAppletContext().showStatus(message);
 199   }
 200
 201   /**
 202    * Returns an image from the specified URL.  Note that the image is not
 203    * actually retrieved until the applet attempts to display it, so this
 204    * method returns immediately.
 205    *
 206    * @param url the URL of the image
 207    * @return the retrieved image
 208    * @throws NullPointerException if url is null
 209    */
 210   public Image getImage(URL url)
 211   {
 212     return getAppletContext().getImage(url);
 213   }
 214
 215   /**
 216    * Returns an image from the specified absolute URL, and relative path
 217    * from that URL.  Note that the image is not actually retrieved until the
 218    * applet attempts to display it, so this method returns immediately.
 219    * This calls <code>getImage(new URL(url, name))</code>, but if building
 220    * the new URL fails, this returns null.
 221    *
 222    * @param url the base URL of the image
 223    * @param name the name of the image relative to the URL
 224    * @return the retrieved image, or null on failure
 225    * @see #getImage(URL)
 226    */
 227   public Image getImage(URL url, String name)
 228   {
 229     try
 230       {
 231         return getImage(new URL(url, name));
 232       }
 233     catch (MalformedURLException e)
 234       {
 235         return null;
 236       }
 237   }
 238
 239   /**
 240    * Returns an audio clip from the specified URL. This clip is not tied to
 241    * any particular applet.
 242    *
 243    * XXX Classpath does not yet implement this.
 244    *
 245    * @param url the URL of the audio clip
 246    * @return the retrieved audio clip
 247    * @throws NullPointerException if url is null
 248    * @see #getAudioClip(URL)
 249    * @since 1.2
 250    */
 251   public static final AudioClip newAudioClip(URL url)
 252   {
 253     // This requires an implementation of AudioClip in gnu.java.applet.
 254     throw new Error("Not implemented");
 255   }
 256
 257   /**
 258    * Returns an audio clip from the specified URL. Note that the clip is not
 259    * actually retrieved until the applet attempts to play it, so this method
 260    * returns immediately.
 261    *
 262    * @param url the URL of the audio clip
 263    * @return the retrieved audio clip
 264    * @throws NullPointerException if url is null
 265    */
 266   public AudioClip getAudioClip(URL url)
 267   {
 268     return getAppletContext().getAudioClip(url);
 269   }
 270
 271   /**
 272    * Returns an audio clip from the specified absolute URL, and relative path
 273    * from that URL.  Note that the clip is not actually retrieved until the
 274    * applet attempts to play it, so this method returns immediately. This
 275    * calls <code>getAudioClip(new URL(url, name))</code>, but if building
 276    * the new URL fails, this returns null.
 277    *
 278    * @param url the base URL of the audio clip
 279    * @param name the name of the clip relative to the URL
 280    * @return the retrieved audio clip, or null on failure
 281    * @see #getAudioClip(URL)
 282    */
 283   public AudioClip getAudioClip(URL url, String name)
 284   {
 285     try
 286       {
 287         return getAudioClip(new URL(url, name));
 288       }
 289     catch (MalformedURLException e)
 290       {
 291         return null;
 292       }
 293   }
 294
 295   /**
 296    * Returns a descriptive string with applet defined information.  The
 297    * implementation in this class returns <code>null</code>, so subclasses
 298    * must override to return information.
 299    *
 300    * @return a string describing the author, version, and applet copyright
 301    */
 302   public String getAppletInfo()
 303   {
 304     return null;
 305   }
 306
 307   /**
 308    * Returns the locale for this applet, if it has been set.  If no applet
 309    * specific locale has been set, the default locale is returned.
 310    *
 311    * @return the locale for this applet
 312    * @see Component#setLocale(Locale)
 313    * @since 1.1
 314    */
 315   public Locale getLocale()
 316   {
 317     return super.getLocale();
 318   }
 319
 320   /**
 321    * Returns a list of parameters this applet supports.  Each element of
 322    * the outer array is an array of three strings with the name of the
 323    * parameter, the data type or valid values, and a description.  This
 324    * method is optional and the default implementation returns null.
 325    *
 326    * @return the list of parameters supported by this applet
 327    */
 328   public String[][] getParameterInfo()
 329   {
 330     return null;
 331   }
 332
 333   /**
 334    * Loads and plays the audio clip pointed to by the specified URL. This does
 335    * nothing if the URL does not point to a valid audio clip.
 336    *
 337    * @param url the URL of the audio clip
 338    * @throws NullPointerException if url is null
 339    * @see #getAudioClip(URL)
 340    */
 341   public void play(URL url)
 342   {
 343     AudioClip ac = getAudioClip(url);
 344     try
 345       {
 346         ac.play();
 347       }
 348     catch (Exception ignored)
 349       {
 350       }
 351   }
 352
 353   /**
 354    * Loads and plays the audio clip pointed to by the specified absolute URL,
 355    * and relative path from that URL. This does nothing if the URL cannot be
 356    * constructed, or if it does not point to a valid audio clip.
 357    *
 358    * @param url the base URL of the audio clip
 359    * @param name the name of the audio clip relative to the URL
 360    * @see #getAudioClip(URL, String)
 361    * @see #play(URL)
 362    */
 363   public void play(URL url, String name)
 364   {
 365     try
 366       {
 367         getAudioClip(url, name).play();
 368       }
 369     catch (Exception ignored)
 370       {
 371       }
 372   }
 373
 374   /**
 375    * This method is called when the applet is first loaded, before start().
 376    * The default implementation does nothing; override to do any one-time
 377    * initialization.
 378    *
 379    * @see #start()
 380    * @see #stop()
 381    * @see #destroy()
 382    */
 383   public void init()
 384   {
 385   }
 386
 387   /**
 388    * This method is called when the applet should start running.  This is
 389    * normally each time a web page containing it is loaded.  The default
 390    * implemention does nothing; override for your applet to be useful.
 391    *
 392    * @see #init()
 393    * @see #stop()
 394    * @see #destroy()
 395    */
 396   public void start()
 397   {
 398   }
 399
 400   /**
 401    * This method is called when the applet should stop running.  This is
 402    * normally when the next web page is loaded.  The default implementation
 403    * does nothing; override for your applet to stop using resources when
 404    * it is no longer visible, but may be restarted soon.
 405    *
 406    * @see #init()
 407    * @see #start()
 408    * @see #destroy()
 409    */
 410   public void stop()
 411   {
 412   }
 413
 414   /**
 415    * This method is called when the applet is being unloaded.  The default
 416    * implementation does nothing; override for your applet to clean up
 417    * resources on exit.
 418    *
 419    * @see #init()
 420    * @see #start()
 421    * @see #stop()
 422    */
 423   public void destroy()
 424   {
 425   }
 426
 427   /**
 428    * Gets the AccessibleContext associated with this applet, creating one if
 429    * necessary. This always returns an instance of {@link AccessibleApplet}.
 430    *
 431    * @return the accessibility context of this applet
 432    * @since 1.3
 433    */
 434   public AccessibleContext getAccessibleContext()
 435   {
 436     if (accessibleContext == null)
 437       accessibleContext = new AccessibleApplet();
 438     return accessibleContext;
 439   }
 440
 441   /**
 442    * Read an applet from an object stream. This checks for a headless
 443    * environment, then does the normal read.
 444    *
 445    * @param s the stream to read from
 446    * @throws ClassNotFoundException if a class is not found
 447    * @throws IOException if deserialization fails
 448    * @throws HeadlessException if this is a headless environment
 449    * @see GraphicsEnvironment#isHeadless()
 450    * @since 1.4
 451    */
 452   private void readObject(ObjectInputStream s)
 453     throws ClassNotFoundException, IOException
 454   {
 455     if (GraphicsEnvironment.isHeadless())
 456       throw new HeadlessException();
 457     s.defaultReadObject();
 458   }
 459
 460   /**
 461    * This class provides accessibility support for Applets, and is the
 462    * runtime type returned by {@link #getAccessibleContext()}.
 463    *
 464    * @author Eric Blake <ebb9@email.byu.edu>
 465    * @since 1.3
 466    */
 467   protected class AccessibleApplet extends AccessibleAWTPanel
 468   {
 469     /**
 470      * Compatible with JDK 1.4+.
 471      */
 472     private static final long serialVersionUID = 8127374778187708896L;
 473
 474     /**
 475      * The default constructor.
 476      */
 477     protected AccessibleApplet()
 478     {
 479     }
 480
 481     /**
 482      * Get the role of this accessible object, a frame.
 483      *
 484      * @return the role of the object
 485      * @see AccessibleRole#FRAME
 486      */
 487     public AccessibleRole getAccessibleRole()
 488     {
 489       return AccessibleRole.FRAME;
 490     }
 491
 492     /**
 493      * Get the state set of this accessible object. In addition to the default
 494      * states of a Component, the applet can also be active.
 495      *
 496      * @return the role of the object
 497      * @see AccessibleState
 498      */
 499     public AccessibleStateSet getAccessibleStateSet()
 500     {
 501       AccessibleStateSet s = super.getAccessibleStateSet();
 502       if (isActive())
 503         s.add(AccessibleState.ACTIVE);
 504       return s;
 505     }
 506   } // class AccessibleApplet
 507 } // class Applet