1 /*
   2  * Copyright (c) 2004, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 
  24 package java.lang;
  25 
  26 import nsk.jvmti.scenarios.bcinstr.BI04.bi04t002a;
  27 
  28 /**
  29  * Class <code>Object</code> is the root of the class hierarchy.
  30  * Every class has <code>Object</code> as a superclass. All objects,
  31  * including arrays, implement the methods of this class.
  32  *
  33  * @author  unascribed
  34  * @version 1.67, 02/03/04
  35  * @see     java.lang.Class
  36  * @since   JDK1.0
  37  */
  38 public class Object {
  39 
  40     private static native void registerNatives();
  41     static {
  42         registerNatives();
  43     }
  44 
  45     /**
  46      * Returns the runtime class of an object. That <tt>Class</tt>
  47      * object is the object that is locked by <tt>static synchronized</tt>
  48      * methods of the represented class.
  49      *
  50      * @return The <code>java.lang.Class</code> object that represents
  51      *         the runtime class of the object.  The result is of type
  52      *         {@code Class<? extends X>} where X is the
  53      *         static type of the expression on which
  54      *         <code>getClass</code> is called.
  55      */
  56     public final native Class<? extends Object> getClass();
  57 
  58     /**
  59      * Returns a hash code value for the object. This method is
  60      * supported for the benefit of hashtables such as those provided by
  61      * <code>java.util.Hashtable</code>.
  62      * <p>
  63      * The general contract of <code>hashCode</code> is:
  64      * <ul>
  65      * <li>Whenever it is invoked on the same object more than once during
  66      *     an execution of a Java application, the <tt>hashCode</tt> method
  67      *     must consistently return the same integer, provided no information
  68      *     used in <tt>equals</tt> comparisons on the object is modified.
  69      *     This integer need not remain consistent from one execution of an
  70      *     application to another execution of the same application.
  71      * <li>If two objects are equal according to the <tt>equals(Object)</tt>
  72      *     method, then calling the <code>hashCode</code> method on each of
  73      *     the two objects must produce the same integer result.
  74      * <li>It is <em>not</em> required that if two objects are unequal
  75      *     according to the {@link java.lang.Object#equals(java.lang.Object)}
  76      *     method, then calling the <tt>hashCode</tt> method on each of the
  77      *     two objects must produce distinct integer results.  However, the
  78      *     programmer should be aware that producing distinct integer results
  79      *     for unequal objects may improve the performance of hashtables.
  80      * </ul>
  81      * <p>
  82      * As much as is reasonably practical, the hashCode method defined by
  83      * class <tt>Object</tt> does return distinct integers for distinct
  84      * objects. (This is typically implemented by converting the internal
  85      * address of the object into an integer, but this implementation
  86      * technique is not required by the
  87      * Java<font size="-2"><sup>TM</sup></font> programming language.)
  88      *
  89      * @return  a hash code value for this object.
  90      * @see     java.lang.Object#equals(java.lang.Object)
  91      * @see     java.util.Hashtable
  92      */
  93     public native int hashCode();
  94 
  95     /**
  96      * Indicates whether some other object is "equal to" this one.
  97      * <p>
  98      * The <code>equals</code> method implements an equivalence relation
  99      * on non-null object references:
 100      * <ul>
 101      * <li>It is <i>reflexive</i>: for any non-null reference value
 102      *     <code>x</code>, <code>x.equals(x)</code> should return
 103      *     <code>true</code>.
 104      * <li>It is <i>symmetric</i>: for any non-null reference values
 105      *     <code>x</code> and <code>y</code>, <code>x.equals(y)</code>
 106      *     should return <code>true</code> if and only if
 107      *     <code>y.equals(x)</code> returns <code>true</code>.
 108      * <li>It is <i>transitive</i>: for any non-null reference values
 109      *     <code>x</code>, <code>y</code>, and <code>z</code>, if
 110      *     <code>x.equals(y)</code> returns <code>true</code> and
 111      *     <code>y.equals(z)</code> returns <code>true</code>, then
 112      *     <code>x.equals(z)</code> should return <code>true</code>.
 113      * <li>It is <i>consistent</i>: for any non-null reference values
 114      *     <code>x</code> and <code>y</code>, multiple invocations of
 115      *     <tt>x.equals(y)</tt> consistently return <code>true</code>
 116      *     or consistently return <code>false</code>, provided no
 117      *     information used in <code>equals</code> comparisons on the
 118      *     objects is modified.
 119      * <li>For any non-null reference value <code>x</code>,
 120      *     <code>x.equals(null)</code> should return <code>false</code>.
 121      * </ul>
 122      * <p>
 123      * The <tt>equals</tt> method for class <code>Object</code> implements
 124      * the most discriminating possible equivalence relation on objects;
 125      * that is, for any non-null reference values <code>x</code> and
 126      * <code>y</code>, this method returns <code>true</code> if and only
 127      * if <code>x</code> and <code>y</code> refer to the same object
 128      * (<code>x == y</code> has the value <code>true</code>).
 129      * <p>
 130      * Note that it is generally necessary to override the <tt>hashCode</tt>
 131      * method whenever this method is overridden, so as to maintain the
 132      * general contract for the <tt>hashCode</tt> method, which states
 133      * that equal objects must have equal hash codes.
 134      *
 135      * @param   obj   the reference object with which to compare.
 136      * @return  <code>true</code> if this object is the same as the obj
 137      *          argument; <code>false</code> otherwise.
 138      * @see     #hashCode()
 139      * @see     java.util.Hashtable
 140      */
 141     public boolean equals(Object obj) {
 142         bi04t002a.instrInvoke(bi04t002a.INSTR_EQUALS);
 143         return (this == obj);
 144     }
 145 
 146     /**
 147      * Creates and returns a copy of this object.  The precise meaning
 148      * of "copy" may depend on the class of the object. The general
 149      * intent is that, for any object <tt>x</tt>, the expression:
 150      * <blockquote>
 151      * <pre>
 152      * x.clone() != x</pre></blockquote>
 153      * will be true, and that the expression:
 154      * <blockquote>
 155      * <pre>
 156      * x.clone().getClass() == x.getClass()</pre></blockquote>
 157      * will be <tt>true</tt>, but these are not absolute requirements.
 158      * While it is typically the case that:
 159      * <blockquote>
 160      * <pre>
 161      * x.clone().equals(x)</pre></blockquote>
 162      * will be <tt>true</tt>, this is not an absolute requirement.
 163      * <p>
 164      * By convention, the returned object should be obtained by calling
 165      * <tt>super.clone</tt>.  If a class and all of its superclasses (except
 166      * <tt>Object</tt>) obey this convention, it will be the case that
 167      * <tt>x.clone().getClass() == x.getClass()</tt>.
 168      * <p>
 169      * By convention, the object returned by this method should be independent
 170      * of this object (which is being cloned).  To achieve this independence,
 171      * it may be necessary to modify one or more fields of the object returned
 172      * by <tt>super.clone</tt> before returning it.  Typically, this means
 173      * copying any mutable objects that comprise the internal "deep structure"
 174      * of the object being cloned and replacing the references to these
 175      * objects with references to the copies.  If a class contains only
 176      * primitive fields or references to immutable objects, then it is usually
 177      * the case that no fields in the object returned by <tt>super.clone</tt>
 178      * need to be modified.
 179      * <p>
 180      * The method <tt>clone</tt> for class <tt>Object</tt> performs a
 181      * specific cloning operation. First, if the class of this object does
 182      * not implement the interface <tt>Cloneable</tt>, then a
 183      * <tt>CloneNotSupportedException</tt> is thrown. Note that all arrays
 184      * are considered to implement the interface <tt>Cloneable</tt>.
 185      * Otherwise, this method creates a new instance of the class of this
 186      * object and initializes all its fields with exactly the contents of
 187      * the corresponding fields of this object, as if by assignment; the
 188      * contents of the fields are not themselves cloned. Thus, this method
 189      * performs a "shallow copy" of this object, not a "deep copy" operation.
 190      * <p>
 191      * The class <tt>Object</tt> does not itself implement the interface
 192      * <tt>Cloneable</tt>, so calling the <tt>clone</tt> method on an object
 193      * whose class is <tt>Object</tt> will result in throwing an
 194      * exception at run time.
 195      *
 196      * @return     a clone of this instance.
 197      * @exception  CloneNotSupportedException  if the object's class does not
 198      *               support the <code>Cloneable</code> interface. Subclasses
 199      *               that override the <code>clone</code> method can also
 200      *               throw this exception to indicate that an instance cannot
 201      *               be cloned.
 202      * @see java.lang.Cloneable
 203      */
 204     protected native Object clone() throws CloneNotSupportedException;
 205 
 206     /**
 207      * Returns a string representation of the object. In general, the
 208      * <code>toString</code> method returns a string that
 209      * "textually represents" this object. The result should
 210      * be a concise but informative representation that is easy for a
 211      * person to read.
 212      * It is recommended that all subclasses override this method.
 213      * <p>
 214      * The <code>toString</code> method for class <code>Object</code>
 215      * returns a string consisting of the name of the class of which the
 216      * object is an instance, the at-sign character `<code>@</code>', and
 217      * the unsigned hexadecimal representation of the hash code of the
 218      * object. In other words, this method returns a string equal to the
 219      * value of:
 220      * <blockquote>
 221      * <pre>
 222      * getClass().getName() + '@' + Integer.toHexString(hashCode())
 223      * </pre></blockquote>
 224      *
 225      * @return  a string representation of the object.
 226      */
 227     public String toString() {
 228         bi04t002a.instrInvoke(bi04t002a.INSTR_TOSTRING);
 229         return getClass().getName() + "@" + Integer.toHexString(hashCode());
 230     }
 231 
 232     /**
 233      * Wakes up a single thread that is waiting on this object's
 234      * monitor. If any threads are waiting on this object, one of them
 235      * is chosen to be awakened. The choice is arbitrary and occurs at
 236      * the discretion of the implementation. A thread waits on an object's
 237      * monitor by calling one of the <code>wait</code> methods.
 238      * <p>
 239      * The awakened thread will not be able to proceed until the current
 240      * thread relinquishes the lock on this object. The awakened thread will
 241      * compete in the usual manner with any other threads that might be
 242      * actively competing to synchronize on this object; for example, the
 243      * awakened thread enjoys no reliable privilege or disadvantage in being
 244      * the next thread to lock this object.
 245      * <p>
 246      * This method should only be called by a thread that is the owner
 247      * of this object's monitor. A thread becomes the owner of the
 248      * object's monitor in one of three ways:
 249      * <ul>
 250      * <li>By executing a synchronized instance method of that object.
 251      * <li>By executing the body of a <code>synchronized</code> statement
 252      *     that synchronizes on the object.
 253      * <li>For objects of type <code>Class,</code> by executing a
 254      *     synchronized static method of that class.
 255      * </ul>
 256      * <p>
 257      * Only one thread at a time can own an object's monitor.
 258      *
 259      * @exception  IllegalMonitorStateException  if the current thread is not
 260      *               the owner of this object's monitor.
 261      * @see        java.lang.Object#notifyAll()
 262      * @see        java.lang.Object#wait()
 263      */
 264     public final native void notify();
 265 
 266     /**
 267      * Wakes up all threads that are waiting on this object's monitor. A
 268      * thread waits on an object's monitor by calling one of the
 269      * <code>wait</code> methods.
 270      * <p>
 271      * The awakened threads will not be able to proceed until the current
 272      * thread relinquishes the lock on this object. The awakened threads
 273      * will compete in the usual manner with any other threads that might
 274      * be actively competing to synchronize on this object; for example,
 275      * the awakened threads enjoy no reliable privilege or disadvantage in
 276      * being the next thread to lock this object.
 277      * <p>
 278      * This method should only be called by a thread that is the owner
 279      * of this object's monitor. See the <code>notify</code> method for a
 280      * description of the ways in which a thread can become the owner of
 281      * a monitor.
 282      *
 283      * @exception  IllegalMonitorStateException  if the current thread is not
 284      *               the owner of this object's monitor.
 285      * @see        java.lang.Object#notify()
 286      * @see        java.lang.Object#wait()
 287      */
 288     public final native void notifyAll();
 289 
 290     /**
 291      * Causes current thread to wait until either another thread invokes the
 292      * {@link java.lang.Object#notify()} method or the
 293      * {@link java.lang.Object#notifyAll()} method for this object, or a
 294      * specified amount of time has elapsed.
 295      * <p>
 296      * The current thread must own this object's monitor.
 297      * <p>
 298      * This method causes the current thread (call it <var>T</var>) to
 299      * place itself in the wait set for this object and then to relinquish
 300      * any and all synchronization claims on this object. Thread <var>T</var>
 301      * becomes disabled for thread scheduling purposes and lies dormant
 302      * until one of four things happens:
 303      * <ul>
 304      * <li>Some other thread invokes the <tt>notify</tt> method for this
 305      * object and thread <var>T</var> happens to be arbitrarily chosen as
 306      * the thread to be awakened.
 307      * <li>Some other thread invokes the <tt>notifyAll</tt> method for this
 308      * object.
 309      * <li>Some other thread {@link java.lang.Thread#interrupt() interrupts}
 310      * thread <var>T</var>.
 311      * <li>The specified amount of real time has elapsed, more or less.  If
 312      * <tt>timeout</tt> is zero, however, then real time is not taken into
 313      * consideration and the thread simply waits until notified.
 314      * </ul>
 315      * The thread <var>T</var> is then removed from the wait set for this
 316      * object and re-enabled for thread scheduling. It then competes in the
 317      * usual manner with other threads for the right to synchronize on the
 318      * object; once it has gained control of the object, all its
 319      * synchronization claims on the object are restored to the status quo
 320      * ante - that is, to the situation as of the time that the <tt>wait</tt>
 321      * method was invoked. Thread <var>T</var> then returns from the
 322      * invocation of the <tt>wait</tt> method. Thus, on return from the
 323      * <tt>wait</tt> method, the synchronization state of the object and of
 324      * thread <tt>T</tt> is exactly as it was when the <tt>wait</tt> method
 325      * was invoked.
 326      * <p>
 327      * A thread can also wake up without being notified, interrupted, or
 328      * timing out, a so-called <i>spurious wakeup</i>.  While this will rarely
 329      * occur in practice, applications must guard against it by testing for
 330      * the condition that should have caused the thread to be awakened, and
 331      * continuing to wait if the condition is not satisfied.  In other words,
 332      * waits should always occur in loops, like this one:
 333      * <pre>
 334      *     synchronized (obj) {
 335      *         while (&lt;condition does not hold&gt;)
 336      *             obj.wait(timeout);
 337      *         ... // Perform action appropriate to condition
 338      *     }
 339      * </pre>
 340      * (For more information on this topic, see Section 3.2.3 in Doug Lea's
 341      * "Concurrent Programming in Java (Second Edition)" (Addison-Wesley,
 342      * 2000), or Item 50 in Joshua Bloch's "Effective Java Programming
 343      * Language Guide" (Addison-Wesley, 2001).
 344      * <p>
 345      * If the current thread is
 346      * {@link java.lang.Thread#interrupt() interrupted} by another thread
 347      * while it is waiting, then an <tt>InterruptedException</tt> is thrown.
 348      * This exception is not thrown until the lock status of this object has
 349      * been restored as described above.
 350      * <p>
 351      * Note that the <tt>wait</tt> method, as it places the current thread
 352      * into the wait set for this object, unlocks only this object; any
 353      * other objects on which the current thread may be synchronized remain
 354      * locked while the thread waits.
 355      * <p>
 356      * This method should only be called by a thread that is the owner
 357      * of this object's monitor. See the <code>notify</code> method for a
 358      * description of the ways in which a thread can become the owner of
 359      * a monitor.
 360      *
 361      * @param      timeout   the maximum time to wait in milliseconds.
 362      * @exception  IllegalArgumentException      if the value of timeout is
 363      *               negative.
 364      * @exception  IllegalMonitorStateException  if the current thread is not
 365      *               the owner of the object's monitor.
 366      * @exception  InterruptedException if another thread interrupted the
 367      *             current thread before or while the current thread
 368      *             was waiting for a notification.  The <i>interrupted
 369      *             status</i> of the current thread is cleared when
 370      *             this exception is thrown.
 371      * @see        java.lang.Object#notify()
 372      * @see        java.lang.Object#notifyAll()
 373      */
 374     public final void wait(long timeoutMillis) throws InterruptedException {
 375         wait0(timeoutMillis);
 376     }
 377 
 378     /**
 379      * Causes current thread to wait until another thread invokes the
 380      * {@link java.lang.Object#notify()} method or the
 381      * {@link java.lang.Object#notifyAll()} method for this object, or
 382      * some other thread interrupts the current thread, or a certain
 383      * amount of real time has elapsed.
 384      * <p>
 385      * This method is similar to the <code>wait</code> method of one
 386      * argument, but it allows finer control over the amount of time to
 387      * wait for a notification before giving up. The amount of real time,
 388      * measured in nanoseconds, is given by:
 389      * <blockquote>
 390      * <pre>
 391      * 1000000*timeout+nanos</pre></blockquote>
 392      * <p>
 393      * In all other respects, this method does the same thing as the
 394      * method {@link #wait(long)} of one argument. In particular,
 395      * <tt>wait(0, 0)</tt> means the same thing as <tt>wait(0)</tt>.
 396      * <p>
 397      * The current thread must own this object's monitor. The thread
 398      * releases ownership of this monitor and waits until either of the
 399      * following two conditions has occurred:
 400      * <ul>
 401      * <li>Another thread notifies threads waiting on this object's monitor
 402      *     to wake up either through a call to the <code>notify</code> method
 403      *     or the <code>notifyAll</code> method.
 404      * <li>The timeout period, specified by <code>timeout</code>
 405      *     milliseconds plus <code>nanos</code> nanoseconds arguments, has
 406      *     elapsed.
 407      * </ul>
 408      * <p>
 409      * The thread then waits until it can re-obtain ownership of the
 410      * monitor and resumes execution.
 411      * <p>
 412      * As in the one argument version, interrupts and spurious wakeups are
 413      * possible, and this method should always be used in a loop:
 414      * <pre>
 415      *     synchronized (obj) {
 416      *         while (&lt;condition does not hold&gt;)
 417      *             obj.wait(timeout, nanos);
 418      *         ... // Perform action appropriate to condition
 419      *     }
 420      * </pre>
 421      * This method should only be called by a thread that is the owner
 422      * of this object's monitor. See the <code>notify</code> method for a
 423      * description of the ways in which a thread can become the owner of
 424      * a monitor.
 425      *
 426      * @param      timeout   the maximum time to wait in milliseconds.
 427      * @param      nanos      additional time, in nanoseconds range
 428      *                       0-999999.
 429      * @exception  IllegalArgumentException      if the value of timeout is
 430      *                      negative or the value of nanos is
 431      *                      not in the range 0-999999.
 432      * @exception  IllegalMonitorStateException  if the current thread is not
 433      *               the owner of this object's monitor.
 434      * @exception  InterruptedException if another thread interrupted the
 435      *             current thread before or while the current thread
 436      *             was waiting for a notification.  The <i>interrupted
 437      *             status</i> of the current thread is cleared when
 438      *             this exception is thrown.
 439      */
 440     public final void wait(long timeout, int nanos) throws InterruptedException {
 441 
 442         bi04t002a.instrInvoke(bi04t002a.INSTR_WAIT_JI);
 443 
 444         if (timeout < 0) {
 445             throw new IllegalArgumentException("timeout value is negative");
 446         }
 447 
 448         if (nanos < 0 || nanos > 999999) {
 449             throw new IllegalArgumentException(
 450                                 "nanosecond timeout value out of range");
 451         }
 452 
 453             if (nanos >= 500000 || (nanos != 0 && timeout == 0)) {
 454                 timeout++;
 455             }
 456 
 457             wait(timeout);
 458     }
 459 
 460     // final modifier so method not in vtable
 461     private final native void wait0(long timeoutMillis) throws InterruptedException;
 462 
 463     /**
 464      * Causes current thread to wait until another thread invokes the
 465      * {@link java.lang.Object#notify()} method or the
 466      * {@link java.lang.Object#notifyAll()} method for this object.
 467      * In other words, this method behaves exactly as if it simply
 468      * performs the call <tt>wait(0)</tt>.
 469      * <p>
 470      * The current thread must own this object's monitor. The thread
 471      * releases ownership of this monitor and waits until another thread
 472      * notifies threads waiting on this object's monitor to wake up
 473      * either through a call to the <code>notify</code> method or the
 474      * <code>notifyAll</code> method. The thread then waits until it can
 475      * re-obtain ownership of the monitor and resumes execution.
 476      * <p>
 477      * As in the one argument version, interrupts and spurious wakeups are
 478      * possible, and this method should always be used in a loop:
 479      * <pre>
 480      *     synchronized (obj) {
 481      *         while (&lt;condition does not hold&gt;)
 482      *             obj.wait();
 483      *         ... // Perform action appropriate to condition
 484      *     }
 485      * </pre>
 486      * This method should only be called by a thread that is the owner
 487      * of this object's monitor. See the <code>notify</code> method for a
 488      * description of the ways in which a thread can become the owner of
 489      * a monitor.
 490      *
 491      * @exception  IllegalMonitorStateException  if the current thread is not
 492      *               the owner of the object's monitor.
 493      * @exception  InterruptedException if another thread interrupted the
 494      *             current thread before or while the current thread
 495      *             was waiting for a notification.  The <i>interrupted
 496      *             status</i> of the current thread is cleared when
 497      *             this exception is thrown.
 498      * @see        java.lang.Object#notify()
 499      * @see        java.lang.Object#notifyAll()
 500      */
 501     public final void wait() throws InterruptedException {
 502         bi04t002a.instrInvoke(bi04t002a.INSTR_WAIT);
 503         wait(0);
 504     }
 505 
 506     /**
 507      * Called by the garbage collector on an object when garbage collection
 508      * determines that there are no more references to the object.
 509      * A subclass overrides the <code>finalize</code> method to dispose of
 510      * system resources or to perform other cleanup.
 511      * <p>
 512      * The general contract of <tt>finalize</tt> is that it is invoked
 513      * if and when the Java<font size="-2"><sup>TM</sup></font> virtual
 514      * machine has determined that there is no longer any
 515      * means by which this object can be accessed by any thread that has
 516      * not yet died, except as a result of an action taken by the
 517      * finalization of some other object or class which is ready to be
 518      * finalized. The <tt>finalize</tt> method may take any action, including
 519      * making this object available again to other threads; the usual purpose
 520      * of <tt>finalize</tt>, however, is to perform cleanup actions before
 521      * the object is irrevocably discarded. For example, the finalize method
 522      * for an object that represents an input/output connection might perform
 523      * explicit I/O transactions to break the connection before the object is
 524      * permanently discarded.
 525      * <p>
 526      * The <tt>finalize</tt> method of class <tt>Object</tt> performs no
 527      * special action; it simply returns normally. Subclasses of
 528      * <tt>Object</tt> may override this definition.
 529      * <p>
 530      * The Java programming language does not guarantee which thread will
 531      * invoke the <tt>finalize</tt> method for any given object. It is
 532      * guaranteed, however, that the thread that invokes finalize will not
 533      * be holding any user-visible synchronization locks when finalize is
 534      * invoked. If an uncaught exception is thrown by the finalize method,
 535      * the exception is ignored and finalization of that object terminates.
 536      * <p>
 537      * After the <tt>finalize</tt> method has been invoked for an object, no
 538      * further action is taken until the Java virtual machine has again
 539      * determined that there is no longer any means by which this object can
 540      * be accessed by any thread that has not yet died, including possible
 541      * actions by other objects or classes which are ready to be finalized,
 542      * at which point the object may be discarded.
 543      * <p>
 544      * The <tt>finalize</tt> method is never invoked more than once by a Java
 545      * virtual machine for any given object.
 546      * <p>
 547      * Any exception thrown by the <code>finalize</code> method causes
 548      * the finalization of this object to be halted, but is otherwise
 549      * ignored.
 550      *
 551      * @throws Throwable the <code>Exception</code> raised by this method
 552      */
 553     protected void finalize() throws Throwable { }
 554 
 555 }