1 /*
   2  * Copyright (c) 1994, 2006, 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.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang;
  27 import  java.io.*;
  28 import  java.util.*;
  29 
  30 /**
  31  * The {@code Throwable} class is the superclass of all errors and
  32  * exceptions in the Java language. Only objects that are instances of this
  33  * class (or one of its subclasses) are thrown by the Java Virtual Machine or
  34  * can be thrown by the Java {@code throw} statement. Similarly, only
  35  * this class or one of its subclasses can be the argument type in a
  36  * {@code catch} clause.
  37  *
  38  * For the purposes of compile-time checking of exceptions, {@code
  39  * Throwable} and any subclass of {@code Throwable} that is not also a
  40  * subclass of either {@link RuntimeException} or {@link Error} are
  41  * regarded as checked exceptions.
  42  *
  43  * <p>Instances of two subclasses, {@link java.lang.Error} and
  44  * {@link java.lang.Exception}, are conventionally used to indicate
  45  * that exceptional situations have occurred. Typically, these instances
  46  * are freshly created in the context of the exceptional situation so
  47  * as to include relevant information (such as stack trace data).
  48  *
  49  * <p>A throwable contains a snapshot of the execution stack of its thread at
  50  * the time it was created. It can also contain a message string that gives
  51  * more information about the error. Finally, it can contain a <i>cause</i>:
  52  * another throwable that caused this throwable to get thrown.  The cause
  53  * facility is new in release 1.4.  It is also known as the <i>chained
  54  * exception</i> facility, as the cause can, itself, have a cause, and so on,
  55  * leading to a "chain" of exceptions, each caused by another.
  56  *
  57  * <p>One reason that a throwable may have a cause is that the class that
  58  * throws it is built atop a lower layered abstraction, and an operation on
  59  * the upper layer fails due to a failure in the lower layer.  It would be bad
  60  * design to let the throwable thrown by the lower layer propagate outward, as
  61  * it is generally unrelated to the abstraction provided by the upper layer.
  62  * Further, doing so would tie the API of the upper layer to the details of
  63  * its implementation, assuming the lower layer's exception was a checked
  64  * exception.  Throwing a "wrapped exception" (i.e., an exception containing a
  65  * cause) allows the upper layer to communicate the details of the failure to
  66  * its caller without incurring either of these shortcomings.  It preserves
  67  * the flexibility to change the implementation of the upper layer without
  68  * changing its API (in particular, the set of exceptions thrown by its
  69  * methods).
  70  *
  71  * <p>A second reason that a throwable may have a cause is that the method
  72  * that throws it must conform to a general-purpose interface that does not
  73  * permit the method to throw the cause directly.  For example, suppose
  74  * a persistent collection conforms to the {@link java.util.Collection
  75  * Collection} interface, and that its persistence is implemented atop
  76  * {@code java.io}.  Suppose the internals of the {@code add} method
  77  * can throw an {@link java.io.IOException IOException}.  The implementation
  78  * can communicate the details of the {@code IOException} to its caller
  79  * while conforming to the {@code Collection} interface by wrapping the
  80  * {@code IOException} in an appropriate unchecked exception.  (The
  81  * specification for the persistent collection should indicate that it is
  82  * capable of throwing such exceptions.)
  83  *
  84  * <p>A cause can be associated with a throwable in two ways: via a
  85  * constructor that takes the cause as an argument, or via the
  86  * {@link #initCause(Throwable)} method.  New throwable classes that
  87  * wish to allow causes to be associated with them should provide constructors
  88  * that take a cause and delegate (perhaps indirectly) to one of the
  89  * {@code Throwable} constructors that takes a cause.  For example:
  90  * <pre>
  91  *     try {
  92  *         lowLevelOp();
  93  *     } catch (LowLevelException le) {
  94  *         throw new HighLevelException(le);  // Chaining-aware constructor
  95  *     }
  96  * </pre>
  97  * Because the {@code initCause} method is public, it allows a cause to be
  98  * associated with any throwable, even a "legacy throwable" whose
  99  * implementation predates the addition of the exception chaining mechanism to
 100  * {@code Throwable}. For example:
 101  * <pre>
 102  *     try {
 103  *         lowLevelOp();
 104  *     } catch (LowLevelException le) {
 105  *         throw (HighLevelException)
 106  *               new HighLevelException().initCause(le);  // Legacy constructor
 107  *     }
 108  * </pre>
 109  *
 110  * <p>Prior to release 1.4, there were many throwables that had their own
 111  * non-standard exception chaining mechanisms (
 112  * {@link ExceptionInInitializerError}, {@link ClassNotFoundException},
 113  * {@link java.lang.reflect.UndeclaredThrowableException},
 114  * {@link java.lang.reflect.InvocationTargetException},
 115  * {@link java.io.WriteAbortedException},
 116  * {@link java.security.PrivilegedActionException},
 117  * {@link java.awt.print.PrinterIOException},
 118  * {@link java.rmi.RemoteException} and
 119  * {@link javax.naming.NamingException}).
 120  * All of these throwables have been retrofitted to
 121  * use the standard exception chaining mechanism, while continuing to
 122  * implement their "legacy" chaining mechanisms for compatibility.
 123  *
 124  * <p>Further, as of release 1.4, many general purpose {@code Throwable}
 125  * classes (for example {@link Exception}, {@link RuntimeException},
 126  * {@link Error}) have been retrofitted with constructors that take
 127  * a cause.  This was not strictly necessary, due to the existence of the
 128  * {@code initCause} method, but it is more convenient and expressive to
 129  * delegate to a constructor that takes a cause.
 130  *
 131  * <p>By convention, class {@code Throwable} and its subclasses have two
 132  * constructors, one that takes no arguments and one that takes a
 133  * {@code String} argument that can be used to produce a detail message.
 134  * Further, those subclasses that might likely have a cause associated with
 135  * them should have two more constructors, one that takes a
 136  * {@code Throwable} (the cause), and one that takes a
 137  * {@code String} (the detail message) and a {@code Throwable} (the
 138  * cause).
 139  *
 140  * <p>Also introduced in release 1.4 is the {@link #getStackTrace()} method,
 141  * which allows programmatic access to the stack trace information that was
 142  * previously available only in text form, via the various forms of the
 143  * {@link #printStackTrace()} method.  This information has been added to the
 144  * <i>serialized representation</i> of this class so {@code getStackTrace}
 145  * and {@code printStackTrace} will operate properly on a throwable that
 146  * was obtained by deserialization.
 147  *
 148  * @author  unascribed
 149  * @author  Josh Bloch (Added exception chaining and programmatic access to
 150  *          stack trace in 1.4.)
 151  * @jls3 11.2 Compile-Time Checking of Exceptions
 152  * @since JDK1.0
 153  */
 154 public class Throwable implements Serializable {
 155     /** use serialVersionUID from JDK 1.0.2 for interoperability */
 156     private static final long serialVersionUID = -3042686055658047285L;
 157 
 158     /**
 159      * Native code saves some indication of the stack backtrace in this slot.
 160      */
 161     private transient Object backtrace;
 162 
 163     /**
 164      * Specific details about the Throwable.  For example, for
 165      * {@code FileNotFoundException}, this contains the name of
 166      * the file that could not be found.
 167      *
 168      * @serial
 169      */
 170     private String detailMessage;
 171 
 172     /**
 173      * The throwable that caused this throwable to get thrown, or null if this
 174      * throwable was not caused by another throwable, or if the causative
 175      * throwable is unknown.  If this field is equal to this throwable itself,
 176      * it indicates that the cause of this throwable has not yet been
 177      * initialized.
 178      *
 179      * @serial
 180      * @since 1.4
 181      */
 182     private Throwable cause = this;
 183 
 184     /**
 185      * The stack trace, as returned by {@link #getStackTrace()}.
 186      *
 187      * @serial
 188      * @since 1.4
 189      */
 190     private StackTraceElement[] stackTrace;
 191     /*
 192      * This field is lazily initialized on first use or serialization and
 193      * nulled out when fillInStackTrace is called.
 194      */
 195 
 196     /**
 197      * The list of suppressed exceptions, as returned by
 198      * {@link #getSuppressedExceptions()}.
 199      *
 200      * @serial
 201      * @since 1.7
 202      */
 203     private List<Throwable> suppressedExceptions = null;
 204     /*
 205      * This field is lazily initialized when the first suppressed
 206      * exception is added.
 207      *
 208      * OutOfMemoryError is preallocated in the VM for better OOM
 209      * diagnosability during VM initialization. Constructor can't
 210      * be not invoked. If a new field to be added in the future must
 211      * be initialized to non-null, it requires a synchronized VM change.
 212      */
 213 
 214     /** Message for trying to suppress a null exception. */
 215     private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
 216 
 217     /** Caption  for labeling causative exception stack traces */
 218     private static final String CAUSE_CAPTION = "Caused by: ";
 219 
 220     /** Caption for labeling suppressed exception stack traces */
 221     private static final String SUPPRESSED_CAPTION = "Suppressed: ";
 222 
 223     /**
 224      * Constructs a new throwable with {@code null} as its detail message.
 225      * The cause is not initialized, and may subsequently be initialized by a
 226      * call to {@link #initCause}.
 227      *
 228      * <p>The {@link #fillInStackTrace()} method is called to initialize
 229      * the stack trace data in the newly created throwable.
 230      */
 231     public Throwable() {
 232         fillInStackTrace();
 233     }
 234 
 235     /**
 236      * Constructs a new throwable with the specified detail message.  The
 237      * cause is not initialized, and may subsequently be initialized by
 238      * a call to {@link #initCause}.
 239      *
 240      * <p>The {@link #fillInStackTrace()} method is called to initialize
 241      * the stack trace data in the newly created throwable.
 242      *
 243      * @param   message   the detail message. The detail message is saved for
 244      *          later retrieval by the {@link #getMessage()} method.
 245      */
 246     public Throwable(String message) {
 247         fillInStackTrace();
 248         detailMessage = message;
 249     }
 250 
 251     /**
 252      * Constructs a new throwable with the specified detail message and
 253      * cause.  <p>Note that the detail message associated with
 254      * {@code cause} is <i>not</i> automatically incorporated in
 255      * this throwable's detail message.
 256      *
 257      * <p>The {@link #fillInStackTrace()} method is called to initialize
 258      * the stack trace data in the newly created throwable.
 259      *
 260      * @param  message the detail message (which is saved for later retrieval
 261      *         by the {@link #getMessage()} method).
 262      * @param  cause the cause (which is saved for later retrieval by the
 263      *         {@link #getCause()} method).  (A {@code null} value is
 264      *         permitted, and indicates that the cause is nonexistent or
 265      *         unknown.)
 266      * @since  1.4
 267      */
 268     public Throwable(String message, Throwable cause) {
 269         fillInStackTrace();
 270         detailMessage = message;
 271         this.cause = cause;
 272     }
 273 
 274     /**
 275      * Constructs a new throwable with the specified cause and a detail
 276      * message of {@code (cause==null ? null : cause.toString())} (which
 277      * typically contains the class and detail message of {@code cause}).
 278      * This constructor is useful for throwables that are little more than
 279      * wrappers for other throwables (for example, {@link
 280      * java.security.PrivilegedActionException}).
 281      *
 282      * <p>The {@link #fillInStackTrace()} method is called to initialize
 283      * the stack trace data in the newly created throwable.
 284      *
 285      * @param  cause the cause (which is saved for later retrieval by the
 286      *         {@link #getCause()} method).  (A {@code null} value is
 287      *         permitted, and indicates that the cause is nonexistent or
 288      *         unknown.)
 289      * @since  1.4
 290      */
 291     public Throwable(Throwable cause) {
 292         fillInStackTrace();
 293         detailMessage = (cause==null ? null : cause.toString());
 294         this.cause = cause;
 295     }
 296 
 297     /**
 298      * Returns the detail message string of this throwable.
 299      *
 300      * @return  the detail message string of this {@code Throwable} instance
 301      *          (which may be {@code null}).
 302      */
 303     public String getMessage() {
 304         return detailMessage;
 305     }
 306 
 307     /**
 308      * Creates a localized description of this throwable.
 309      * Subclasses may override this method in order to produce a
 310      * locale-specific message.  For subclasses that do not override this
 311      * method, the default implementation returns the same result as
 312      * {@code getMessage()}.
 313      *
 314      * @return  The localized description of this throwable.
 315      * @since   JDK1.1
 316      */
 317     public String getLocalizedMessage() {
 318         return getMessage();
 319     }
 320 
 321     /**
 322      * Returns the cause of this throwable or {@code null} if the
 323      * cause is nonexistent or unknown.  (The cause is the throwable that
 324      * caused this throwable to get thrown.)
 325      *
 326      * <p>This implementation returns the cause that was supplied via one of
 327      * the constructors requiring a {@code Throwable}, or that was set after
 328      * creation with the {@link #initCause(Throwable)} method.  While it is
 329      * typically unnecessary to override this method, a subclass can override
 330      * it to return a cause set by some other means.  This is appropriate for
 331      * a "legacy chained throwable" that predates the addition of chained
 332      * exceptions to {@code Throwable}.  Note that it is <i>not</i>
 333      * necessary to override any of the {@code PrintStackTrace} methods,
 334      * all of which invoke the {@code getCause} method to determine the
 335      * cause of a throwable.
 336      *
 337      * @return  the cause of this throwable or {@code null} if the
 338      *          cause is nonexistent or unknown.
 339      * @since 1.4
 340      */
 341     public synchronized Throwable getCause() {
 342         return (cause==this ? null : cause);
 343     }
 344 
 345     /**
 346      * Initializes the <i>cause</i> of this throwable to the specified value.
 347      * (The cause is the throwable that caused this throwable to get thrown.)
 348      *
 349      * <p>This method can be called at most once.  It is generally called from
 350      * within the constructor, or immediately after creating the
 351      * throwable.  If this throwable was created
 352      * with {@link #Throwable(Throwable)} or
 353      * {@link #Throwable(String,Throwable)}, this method cannot be called
 354      * even once.
 355      *
 356      * @param  cause the cause (which is saved for later retrieval by the
 357      *         {@link #getCause()} method).  (A {@code null} value is
 358      *         permitted, and indicates that the cause is nonexistent or
 359      *         unknown.)
 360      * @return  a reference to this {@code Throwable} instance.
 361      * @throws IllegalArgumentException if {@code cause} is this
 362      *         throwable.  (A throwable cannot be its own cause.)
 363      * @throws IllegalStateException if this throwable was
 364      *         created with {@link #Throwable(Throwable)} or
 365      *         {@link #Throwable(String,Throwable)}, or this method has already
 366      *         been called on this throwable.
 367      * @since  1.4
 368      */
 369     public synchronized Throwable initCause(Throwable cause) {
 370         if (this.cause != this)
 371             throw new IllegalStateException("Can't overwrite cause");
 372         if (cause == this)
 373             throw new IllegalArgumentException("Self-causation not permitted");
 374         this.cause = cause;
 375         return this;
 376     }
 377 
 378     /**
 379      * Returns a short description of this throwable.
 380      * The result is the concatenation of:
 381      * <ul>
 382      * <li> the {@linkplain Class#getName() name} of the class of this object
 383      * <li> ": " (a colon and a space)
 384      * <li> the result of invoking this object's {@link #getLocalizedMessage}
 385      *      method
 386      * </ul>
 387      * If {@code getLocalizedMessage} returns {@code null}, then just
 388      * the class name is returned.
 389      *
 390      * @return a string representation of this throwable.
 391      */
 392     public String toString() {
 393         String s = getClass().getName();
 394         String message = getLocalizedMessage();
 395         return (message != null) ? (s + ": " + message) : s;
 396     }
 397 
 398     /**
 399      * Prints this throwable and its backtrace to the
 400      * standard error stream. This method prints a stack trace for this
 401      * {@code Throwable} object on the error output stream that is
 402      * the value of the field {@code System.err}. The first line of
 403      * output contains the result of the {@link #toString()} method for
 404      * this object.  Remaining lines represent data previously recorded by
 405      * the method {@link #fillInStackTrace()}. The format of this
 406      * information depends on the implementation, but the following
 407      * example may be regarded as typical:
 408      * <blockquote><pre>
 409      * java.lang.NullPointerException
 410      *         at MyClass.mash(MyClass.java:9)
 411      *         at MyClass.crunch(MyClass.java:6)
 412      *         at MyClass.main(MyClass.java:3)
 413      * </pre></blockquote>
 414      * This example was produced by running the program:
 415      * <pre>
 416      * class MyClass {
 417      *     public static void main(String[] args) {
 418      *         crunch(null);
 419      *     }
 420      *     static void crunch(int[] a) {
 421      *         mash(a);
 422      *     }
 423      *     static void mash(int[] b) {
 424      *         System.out.println(b[0]);
 425      *     }
 426      * }
 427      * </pre>
 428      * The backtrace for a throwable with an initialized, non-null cause
 429      * should generally include the backtrace for the cause.  The format
 430      * of this information depends on the implementation, but the following
 431      * example may be regarded as typical:
 432      * <pre>
 433      * HighLevelException: MidLevelException: LowLevelException
 434      *         at Junk.a(Junk.java:13)
 435      *         at Junk.main(Junk.java:4)
 436      * Caused by: MidLevelException: LowLevelException
 437      *         at Junk.c(Junk.java:23)
 438      *         at Junk.b(Junk.java:17)
 439      *         at Junk.a(Junk.java:11)
 440      *         ... 1 more
 441      * Caused by: LowLevelException
 442      *         at Junk.e(Junk.java:30)
 443      *         at Junk.d(Junk.java:27)
 444      *         at Junk.c(Junk.java:21)
 445      *         ... 3 more
 446      * </pre>
 447      * Note the presence of lines containing the characters {@code "..."}.
 448      * These lines indicate that the remainder of the stack trace for this
 449      * exception matches the indicated number of frames from the bottom of the
 450      * stack trace of the exception that was caused by this exception (the
 451      * "enclosing" exception).  This shorthand can greatly reduce the length
 452      * of the output in the common case where a wrapped exception is thrown
 453      * from same method as the "causative exception" is caught.  The above
 454      * example was produced by running the program:
 455      * <pre>
 456      * public class Junk {
 457      *     public static void main(String args[]) {
 458      *         try {
 459      *             a();
 460      *         } catch(HighLevelException e) {
 461      *             e.printStackTrace();
 462      *         }
 463      *     }
 464      *     static void a() throws HighLevelException {
 465      *         try {
 466      *             b();
 467      *         } catch(MidLevelException e) {
 468      *             throw new HighLevelException(e);
 469      *         }
 470      *     }
 471      *     static void b() throws MidLevelException {
 472      *         c();
 473      *     }
 474      *     static void c() throws MidLevelException {
 475      *         try {
 476      *             d();
 477      *         } catch(LowLevelException e) {
 478      *             throw new MidLevelException(e);
 479      *         }
 480      *     }
 481      *     static void d() throws LowLevelException {
 482      *        e();
 483      *     }
 484      *     static void e() throws LowLevelException {
 485      *         throw new LowLevelException();
 486      *     }
 487      * }
 488      *
 489      * class HighLevelException extends Exception {
 490      *     HighLevelException(Throwable cause) { super(cause); }
 491      * }
 492      *
 493      * class MidLevelException extends Exception {
 494      *     MidLevelException(Throwable cause)  { super(cause); }
 495      * }
 496      *
 497      * class LowLevelException extends Exception {
 498      * }
 499      * </pre>
 500      * As of release 7, the platform supports the notion of
 501      * <i>suppressed exceptions</i> (in conjunction with the {@code
 502      * try}-with-resources statement). Any exceptions that were
 503      * suppressed in order to deliver an exception are printed out
 504      * beneath the stack trace.  The format of this information
 505      * depends on the implementation, but the following example may be
 506      * regarded as typical:
 507      *
 508      * <pre>
 509      * Exception in thread "main" java.lang.Exception: Something happened
 510      *  at Foo.bar(Foo.java:10)
 511      *  at Foo.main(Foo.java:5)
 512      *  Suppressed: Resource$CloseFailException: Resource ID = 0
 513      *          at Resource.close(Resource.java:26)
 514      *          at Foo.bar(Foo.java:9)
 515      *          ... 1 more
 516      * </pre>
 517      * Note that the "... n more" notation is used on suppressed exceptions
 518      * just at it is used on causes. Unlike causes, suppressed exceptions are
 519      * indented beyond their "containing exceptions."
 520      *
 521      * <p>An exception can have both a cause and one or more suppressed
 522      * exceptions:
 523      * <pre>
 524      * Exception in thread "main" java.lang.Exception: Main block
 525      *  at Foo3.main(Foo3.java:7)
 526      *  Suppressed: Resource$CloseFailException: Resource ID = 2
 527      *          at Resource.close(Resource.java:26)
 528      *          at Foo3.main(Foo3.java:5)
 529      *  Suppressed: Resource$CloseFailException: Resource ID = 1
 530      *          at Resource.close(Resource.java:26)
 531      *          at Foo3.main(Foo3.java:5)
 532      * Caused by: java.lang.Exception: I did it
 533      *  at Foo3.main(Foo3.java:8)
 534      * </pre>
 535      * Likewise, a suppressed exception can have a cause:
 536      * <pre>
 537      * Exception in thread "main" java.lang.Exception: Main block
 538      *  at Foo4.main(Foo4.java:6)
 539      *  Suppressed: Resource2$CloseFailException: Resource ID = 1
 540      *          at Resource2.close(Resource2.java:20)
 541      *          at Foo4.main(Foo4.java:5)
 542      *  Caused by: java.lang.Exception: Rats, you caught me
 543      *          at Resource2$CloseFailException.<init>(Resource2.java:45)
 544      *          ... 2 more
 545      * </pre>
 546      */
 547     public void printStackTrace() {
 548         printStackTrace(System.err);
 549     }
 550 
 551     /**
 552      * Prints this throwable and its backtrace to the specified print stream.
 553      *
 554      * @param s {@code PrintStream} to use for output
 555      */
 556     public void printStackTrace(PrintStream s) {
 557         printStackTrace(new WrappedPrintStream(s));
 558     }
 559 
 560     private void printStackTrace(PrintStreamOrWriter s) {
 561         // Guard against malicious overrides of Throwable.equals by
 562         // using a Set with identity equality semantics.
 563         Set<Throwable> dejaVu =
 564             Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
 565         dejaVu.add(this);
 566 
 567         synchronized (s.lock()) {
 568             // Print our stack trace
 569             s.println(this);
 570             StackTraceElement[] trace = getOurStackTrace();
 571             for (StackTraceElement traceElement : trace)
 572                 s.println("\tat " + traceElement);
 573 
 574             // Print suppressed exceptions, if any
 575             for (Throwable se : getSuppressedExceptions())
 576                 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
 577 
 578             // Print cause, if any
 579             Throwable ourCause = getCause();
 580             if (ourCause != null)
 581                 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
 582         }
 583     }
 584 
 585     /**
 586      * Print our stack trace as an enclosed exception for the specified
 587      * stack trace.
 588      */
 589     private void printEnclosedStackTrace(PrintStreamOrWriter s,
 590                                          StackTraceElement[] enclosingTrace,
 591                                          String caption,
 592                                          String prefix,
 593                                          Set<Throwable> dejaVu) {
 594         assert Thread.holdsLock(s.lock());
 595         if (dejaVu.contains(this)) {
 596             s.println("\t[CIRCULAR REFERENCE:" + this + "]");
 597         } else {
 598             dejaVu.add(this);
 599             // Compute number of frames in common between this and enclosing trace
 600             StackTraceElement[] trace = getOurStackTrace();
 601             int m = trace.length - 1;
 602             int n = enclosingTrace.length - 1;
 603             while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
 604                 m--; n--;
 605             }
 606             int framesInCommon = trace.length - 1 - m;
 607 
 608             // Print our stack trace
 609             s.println(prefix + caption + this);
 610             for (int i = 0; i <= m; i++)
 611                 s.println(prefix + "\tat " + trace[i]);
 612             if (framesInCommon != 0)
 613                 s.println(prefix + "\t... " + framesInCommon + " more");
 614 
 615             // Print suppressed exceptions, if any
 616             for (Throwable se : getSuppressedExceptions())
 617                 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
 618                                            prefix +"\t", dejaVu);
 619 
 620             // Print cause, if any
 621             Throwable ourCause = getCause();
 622             if (ourCause != null)
 623                 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
 624         }
 625     }
 626 
 627     /**
 628      * Prints this throwable and its backtrace to the specified
 629      * print writer.
 630      *
 631      * @param s {@code PrintWriter} to use for output
 632      * @since   JDK1.1
 633      */
 634     public void printStackTrace(PrintWriter s) {
 635         printStackTrace(new WrappedPrintWriter(s));
 636     }
 637 
 638     /**
 639      * Wrapper class for PrintStream and PrintWriter to enable a single
 640      * implementation of printStackTrace.
 641      */
 642     private abstract static class PrintStreamOrWriter {
 643         /** Returns the object to be locked when using this StreamOrWriter */
 644         abstract Object lock();
 645 
 646         /** Prints the specified string as a line on this StreamOrWriter */
 647         abstract void println(Object o);
 648     }
 649 
 650     private static class WrappedPrintStream extends PrintStreamOrWriter {
 651         private final PrintStream printStream;
 652 
 653         WrappedPrintStream(PrintStream printStream) {
 654             this.printStream = printStream;
 655         }
 656 
 657         Object lock() {
 658             return printStream;
 659         }
 660 
 661         void println(Object o) {
 662             printStream.println(o);
 663         }
 664     }
 665 
 666     private static class WrappedPrintWriter extends PrintStreamOrWriter {
 667         private final PrintWriter printWriter;
 668 
 669         WrappedPrintWriter(PrintWriter printWriter) {
 670             this.printWriter = printWriter;
 671         }
 672 
 673         Object lock() {
 674             return printWriter;
 675         }
 676 
 677         void println(Object o) {
 678             printWriter.println(o);
 679         }
 680     }
 681 
 682     /**
 683      * Fills in the execution stack trace. This method records within this
 684      * {@code Throwable} object information about the current state of
 685      * the stack frames for the current thread.
 686      *
 687      * @return  a reference to this {@code Throwable} instance.
 688      * @see     java.lang.Throwable#printStackTrace()
 689      */
 690     public synchronized native Throwable fillInStackTrace();
 691 
 692     /**
 693      * Provides programmatic access to the stack trace information printed by
 694      * {@link #printStackTrace()}.  Returns an array of stack trace elements,
 695      * each representing one stack frame.  The zeroth element of the array
 696      * (assuming the array's length is non-zero) represents the top of the
 697      * stack, which is the last method invocation in the sequence.  Typically,
 698      * this is the point at which this throwable was created and thrown.
 699      * The last element of the array (assuming the array's length is non-zero)
 700      * represents the bottom of the stack, which is the first method invocation
 701      * in the sequence.
 702      *
 703      * <p>Some virtual machines may, under some circumstances, omit one
 704      * or more stack frames from the stack trace.  In the extreme case,
 705      * a virtual machine that has no stack trace information concerning
 706      * this throwable is permitted to return a zero-length array from this
 707      * method.  Generally speaking, the array returned by this method will
 708      * contain one element for every frame that would be printed by
 709      * {@code printStackTrace}.
 710      *
 711      * @return an array of stack trace elements representing the stack trace
 712      *         pertaining to this throwable.
 713      * @since  1.4
 714      */
 715     public StackTraceElement[] getStackTrace() {
 716         return getOurStackTrace().clone();
 717     }
 718 
 719     private synchronized StackTraceElement[] getOurStackTrace() {
 720         // Initialize stack trace if this is the first call to this method
 721         if (stackTrace == null) {
 722             int depth = getStackTraceDepth();
 723             stackTrace = new StackTraceElement[depth];
 724             for (int i=0; i < depth; i++)
 725                 stackTrace[i] = getStackTraceElement(i);
 726         }
 727         return stackTrace;
 728     }
 729 
 730     /**
 731      * Sets the stack trace elements that will be returned by
 732      * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
 733      * and related methods.
 734      *
 735      * This method, which is designed for use by RPC frameworks and other
 736      * advanced systems, allows the client to override the default
 737      * stack trace that is either generated by {@link #fillInStackTrace()}
 738      * when a throwable is constructed or deserialized when a throwable is
 739      * read from a serialization stream.
 740      *
 741      * @param   stackTrace the stack trace elements to be associated with
 742      * this {@code Throwable}.  The specified array is copied by this
 743      * call; changes in the specified array after the method invocation
 744      * returns will have no affect on this {@code Throwable}'s stack
 745      * trace.
 746      *
 747      * @throws NullPointerException if {@code stackTrace} is
 748      *         {@code null}, or if any of the elements of
 749      *         {@code stackTrace} are {@code null}
 750      *
 751      * @since  1.4
 752      */
 753     public void setStackTrace(StackTraceElement[] stackTrace) {
 754         StackTraceElement[] defensiveCopy = stackTrace.clone();
 755         for (int i = 0; i < defensiveCopy.length; i++)
 756             if (defensiveCopy[i] == null)
 757                 throw new NullPointerException("stackTrace[" + i + "]");
 758 
 759         synchronized (this) {
 760             this.stackTrace = defensiveCopy;
 761         }
 762     }
 763 
 764     /**
 765      * Returns the number of elements in the stack trace (or 0 if the stack
 766      * trace is unavailable).
 767      *
 768      * package-protection for use by SharedSecrets.
 769      */
 770     native int getStackTraceDepth();
 771 
 772     /**
 773      * Returns the specified element of the stack trace.
 774      *
 775      * package-protection for use by SharedSecrets.
 776      *
 777      * @param index index of the element to return.
 778      * @throws IndexOutOfBoundsException if {@code index < 0 ||
 779      *         index >= getStackTraceDepth() }
 780      */
 781     native StackTraceElement getStackTraceElement(int index);
 782 
 783     private void readObject(ObjectInputStream s)
 784         throws IOException, ClassNotFoundException {
 785         s.defaultReadObject();     // read in all fields
 786         List<Throwable> suppressed = null;
 787         if (suppressedExceptions != null &&
 788             !suppressedExceptions.isEmpty()) { // Copy Throwables to new list
 789             suppressed = new ArrayList<Throwable>();
 790             for (Throwable t : suppressedExceptions) {
 791                 if (t == null)
 792                     throw new NullPointerException(NULL_CAUSE_MESSAGE);
 793                 suppressed.add(t);
 794             }
 795         }
 796         suppressedExceptions = suppressed;
 797     }
 798 
 799     private synchronized void writeObject(ObjectOutputStream s)
 800         throws IOException
 801     {
 802         getOurStackTrace();  // Ensure that stackTrace field is initialized.
 803         s.defaultWriteObject();
 804     }
 805 
 806     /**
 807      * Adds the specified exception to the list of exceptions that
 808      * were suppressed, typically by the {@code try}-with-resources
 809      * statement, in order to deliver this exception.
 810      *
 811      * <p>Note that when one exception {@linkplain
 812      * #initCause(Throwable) causes} another exception, the first
 813      * exception is usually caught and then the second exception is
 814      * thrown in response.  In contrast, when one exception suppresses
 815      * another, two exceptions are thrown in sibling code blocks, such
 816      * as in a {@code try} block and in its {@code finally} block, and
 817      * control flow can only continue with one exception so the second
 818      * is recorded as a suppressed exception of the first.
 819      *
 820      * @param exception the exception to be added to the list of
 821      *        suppressed exceptions
 822      * @throws NullPointerException if {@code exception} is null
 823      * @throws IllegalArgumentException if {@code exception} is this
 824      *         throwable; a throwable cannot suppress itself.
 825      * @since 1.7
 826      */
 827     public synchronized void addSuppressedException(Throwable exception) {
 828         if (exception == null)
 829             throw new NullPointerException(NULL_CAUSE_MESSAGE);
 830         if (exception == this)
 831             throw new IllegalArgumentException("Self-suppression not permitted");
 832 
 833         if (suppressedExceptions == null)
 834             suppressedExceptions = new ArrayList<Throwable>();
 835         suppressedExceptions.add(exception);
 836     }
 837 
 838     private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
 839 
 840     /**
 841      * Returns an array containing all of the exceptions that were
 842      * suppressed, typically by the {@code try}-with-resources
 843      * statement, in order to deliver this exception.
 844      *
 845      * @return an array containing all of the exceptions that were
 846      *         suppressed to deliver this exception.
 847      * @since 1.7
 848      */
 849     public synchronized Throwable[] getSuppressedExceptions() {
 850         if (suppressedExceptions == null)
 851             return EMPTY_THROWABLE_ARRAY;
 852         else
 853             return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
 854     }
 855 }