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</code> 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</code> statement. Similarly, only
35 * this class or one of its subclasses can be the argument type in a
36 * <code>catch</code> 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 * <tt>java.io</tt>. Suppose the internals of the <tt>add</tt> method
77 * can throw an {@link java.io.IOException IOException}. The implementation
78 * can communicate the details of the <tt>IOException</tt> to its caller
79 * while conforming to the <tt>Collection</tt> interface by wrapping the
80 * <tt>IOException</tt> 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 * <tt>Throwable</tt> 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 <tt>initCause</tt> 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 * <tt>Throwable</tt>. 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 <tt>Throwable</tt>
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 * <tt>initCause</tt> 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</code> and its subclasses have two
132 * constructors, one that takes no arguments and one that takes a
133 * <code>String</code> 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</code> (the cause), and one that takes a
137 * <code>String</code> (the detail message) and a <code>Throwable</code> (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 <tt>getStackTrace</tt>
145 * and <tt>printStackTrace</tt> 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 * <tt>FileNotFoundException</tt>, 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()}.
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 = Collections.emptyList();
204
205 /** Message for trying to suppress a null exception. */
206 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
207
208 /** Caption for labeling causative exception stack traces */
209 private static final String CAUSE_CAPTION = "Caused by: ";
210
211 /** Caption for labeling suppressed exception stack traces */
212 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
213
214 /**
215 * Constructs a new throwable with <code>null</code> as its detail message.
216 * The cause is not initialized, and may subsequently be initialized by a
217 * call to {@link #initCause}.
218 *
219 * <p>The {@link #fillInStackTrace()} method is called to initialize
220 * the stack trace data in the newly created throwable.
221 */
222 public Throwable() {
223 fillInStackTrace();
224 }
225
226 /**
227 * Constructs a new throwable with the specified detail message. The
228 * cause is not initialized, and may subsequently be initialized by
229 * a call to {@link #initCause}.
230 *
231 * <p>The {@link #fillInStackTrace()} method is called to initialize
232 * the stack trace data in the newly created throwable.
233 *
234 * @param message the detail message. The detail message is saved for
235 * later retrieval by the {@link #getMessage()} method.
236 */
237 public Throwable(String message) {
238 fillInStackTrace();
239 detailMessage = message;
240 }
241
242 /**
243 * Constructs a new throwable with the specified detail message and
244 * cause. <p>Note that the detail message associated with
245 * <code>cause</code> is <i>not</i> automatically incorporated in
246 * this throwable's detail message.
247 *
248 * <p>The {@link #fillInStackTrace()} method is called to initialize
249 * the stack trace data in the newly created throwable.
250 *
251 * @param message the detail message (which is saved for later retrieval
252 * by the {@link #getMessage()} method).
253 * @param cause the cause (which is saved for later retrieval by the
254 * {@link #getCause()} method). (A <tt>null</tt> value is
255 * permitted, and indicates that the cause is nonexistent or
256 * unknown.)
257 * @since 1.4
258 */
259 public Throwable(String message, Throwable cause) {
260 fillInStackTrace();
261 detailMessage = message;
262 this.cause = cause;
263 }
264
265 /**
266 * Constructs a new throwable with the specified cause and a detail
267 * message of <tt>(cause==null ? null : cause.toString())</tt> (which
268 * typically contains the class and detail message of <tt>cause</tt>).
269 * This constructor is useful for throwables that are little more than
270 * wrappers for other throwables (for example, {@link
271 * java.security.PrivilegedActionException}).
272 *
273 * <p>The {@link #fillInStackTrace()} method is called to initialize
274 * the stack trace data in the newly created throwable.
275 *
276 * @param cause the cause (which is saved for later retrieval by the
277 * {@link #getCause()} method). (A <tt>null</tt> value is
278 * permitted, and indicates that the cause is nonexistent or
279 * unknown.)
280 * @since 1.4
281 */
282 public Throwable(Throwable cause) {
283 fillInStackTrace();
284 detailMessage = (cause==null ? null : cause.toString());
285 this.cause = cause;
286 }
287
288 /**
289 * Returns the detail message string of this throwable.
290 *
291 * @return the detail message string of this <tt>Throwable</tt> instance
292 * (which may be <tt>null</tt>).
293 */
294 public String getMessage() {
295 return detailMessage;
296 }
297
298 /**
299 * Creates a localized description of this throwable.
300 * Subclasses may override this method in order to produce a
301 * locale-specific message. For subclasses that do not override this
302 * method, the default implementation returns the same result as
303 * <code>getMessage()</code>.
304 *
305 * @return The localized description of this throwable.
306 * @since JDK1.1
307 */
308 public String getLocalizedMessage() {
309 return getMessage();
310 }
311
312 /**
313 * Returns the cause of this throwable or <code>null</code> if the
314 * cause is nonexistent or unknown. (The cause is the throwable that
315 * caused this throwable to get thrown.)
316 *
317 * <p>This implementation returns the cause that was supplied via one of
318 * the constructors requiring a <tt>Throwable</tt>, or that was set after
319 * creation with the {@link #initCause(Throwable)} method. While it is
320 * typically unnecessary to override this method, a subclass can override
321 * it to return a cause set by some other means. This is appropriate for
322 * a "legacy chained throwable" that predates the addition of chained
323 * exceptions to <tt>Throwable</tt>. Note that it is <i>not</i>
324 * necessary to override any of the <tt>PrintStackTrace</tt> methods,
325 * all of which invoke the <tt>getCause</tt> method to determine the
326 * cause of a throwable.
327 *
328 * @return the cause of this throwable or <code>null</code> if the
329 * cause is nonexistent or unknown.
330 * @since 1.4
331 */
332 public Throwable getCause() {
333 return (cause==this ? null : cause);
334 }
335
336 /**
337 * Initializes the <i>cause</i> of this throwable to the specified value.
338 * (The cause is the throwable that caused this throwable to get thrown.)
339 *
340 * <p>This method can be called at most once. It is generally called from
341 * within the constructor, or immediately after creating the
342 * throwable. If this throwable was created
343 * with {@link #Throwable(Throwable)} or
344 * {@link #Throwable(String,Throwable)}, this method cannot be called
345 * even once.
346 *
347 * @param cause the cause (which is saved for later retrieval by the
348 * {@link #getCause()} method). (A <tt>null</tt> value is
349 * permitted, and indicates that the cause is nonexistent or
350 * unknown.)
351 * @return a reference to this <code>Throwable</code> instance.
352 * @throws IllegalArgumentException if <code>cause</code> is this
353 * throwable. (A throwable cannot be its own cause.)
354 * @throws IllegalStateException if this throwable was
355 * created with {@link #Throwable(Throwable)} or
356 * {@link #Throwable(String,Throwable)}, or this method has already
357 * been called on this throwable.
358 * @since 1.4
359 */
360 public synchronized Throwable initCause(Throwable cause) {
361 if (this.cause != this)
362 throw new IllegalStateException("Can't overwrite cause");
363 if (cause == this)
364 throw new IllegalArgumentException("Self-causation not permitted");
365 this.cause = cause;
366 return this;
367 }
368
369 /**
370 * Returns a short description of this throwable.
371 * The result is the concatenation of:
372 * <ul>
373 * <li> the {@linkplain Class#getName() name} of the class of this object
374 * <li> ": " (a colon and a space)
375 * <li> the result of invoking this object's {@link #getLocalizedMessage}
376 * method
377 * </ul>
378 * If <tt>getLocalizedMessage</tt> returns <tt>null</tt>, then just
379 * the class name is returned.
380 *
381 * @return a string representation of this throwable.
382 */
383 public String toString() {
384 String s = getClass().getName();
385 String message = getLocalizedMessage();
386 return (message != null) ? (s + ": " + message) : s;
387 }
388
389 /**
390 * Prints this throwable and its backtrace to the
391 * standard error stream. This method prints a stack trace for this
392 * <code>Throwable</code> object on the error output stream that is
393 * the value of the field <code>System.err</code>. The first line of
394 * output contains the result of the {@link #toString()} method for
395 * this object. Remaining lines represent data previously recorded by
396 * the method {@link #fillInStackTrace()}. The format of this
397 * information depends on the implementation, but the following
398 * example may be regarded as typical:
399 * <blockquote><pre>
400 * java.lang.NullPointerException
401 * at MyClass.mash(MyClass.java:9)
402 * at MyClass.crunch(MyClass.java:6)
403 * at MyClass.main(MyClass.java:3)
404 * </pre></blockquote>
405 * This example was produced by running the program:
406 * <pre>
407 * class MyClass {
408 * public static void main(String[] args) {
409 * crunch(null);
410 * }
411 * static void crunch(int[] a) {
412 * mash(a);
413 * }
418 * </pre>
419 * The backtrace for a throwable with an initialized, non-null cause
420 * should generally include the backtrace for the cause. The format
421 * of this information depends on the implementation, but the following
422 * example may be regarded as typical:
423 * <pre>
424 * HighLevelException: MidLevelException: LowLevelException
425 * at Junk.a(Junk.java:13)
426 * at Junk.main(Junk.java:4)
427 * Caused by: MidLevelException: LowLevelException
428 * at Junk.c(Junk.java:23)
429 * at Junk.b(Junk.java:17)
430 * at Junk.a(Junk.java:11)
431 * ... 1 more
432 * Caused by: LowLevelException
433 * at Junk.e(Junk.java:30)
434 * at Junk.d(Junk.java:27)
435 * at Junk.c(Junk.java:21)
436 * ... 3 more
437 * </pre>
438 * Note the presence of lines containing the characters <tt>"..."</tt>.
439 * These lines indicate that the remainder of the stack trace for this
440 * exception matches the indicated number of frames from the bottom of the
441 * stack trace of the exception that was caused by this exception (the
442 * "enclosing" exception). This shorthand can greatly reduce the length
443 * of the output in the common case where a wrapped exception is thrown
444 * from same method as the "causative exception" is caught. The above
445 * example was produced by running the program:
446 * <pre>
447 * public class Junk {
448 * public static void main(String args[]) {
449 * try {
450 * a();
451 * } catch(HighLevelException e) {
452 * e.printStackTrace();
453 * }
454 * }
455 * static void a() throws HighLevelException {
456 * try {
457 * b();
458 * } catch(MidLevelException e) {
525 * </pre>
526 * Likewise, a suppressed exception can have a cause:
527 * <pre>
528 * Exception in thread "main" java.lang.Exception: Main block
529 * at Foo4.main(Foo4.java:6)
530 * Suppressed: Resource2$CloseFailException: Resource ID = 1
531 * at Resource2.close(Resource2.java:20)
532 * at Foo4.main(Foo4.java:5)
533 * Caused by: java.lang.Exception: Rats, you caught me
534 * at Resource2$CloseFailException.<init>(Resource2.java:45)
535 * ... 2 more
536 * </pre>
537 */
538 public void printStackTrace() {
539 printStackTrace(System.err);
540 }
541
542 /**
543 * Prints this throwable and its backtrace to the specified print stream.
544 *
545 * @param s <code>PrintStream</code> to use for output
546 */
547 public void printStackTrace(PrintStream s) {
548 printStackTrace(new WrappedPrintStream(s));
549 }
550
551 private void printStackTrace(PrintStreamOrWriter s) {
552 Set<Throwable> dejaVu = new HashSet<Throwable>();
553 dejaVu.add(this);
554
555 synchronized (s.lock()) {
556 // Print our stack trace
557 s.println(this);
558 StackTraceElement[] trace = getOurStackTrace();
559 for (StackTraceElement traceElement : trace)
560 s.println("\tat " + traceElement);
561
562 // Print suppressed exceptions, if any
563 for (Throwable se : suppressedExceptions)
564 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
565
566 // Print cause, if any
567 Throwable ourCause = getCause();
568 if (ourCause != null)
569 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
570 }
571 }
572
599 s.println(prefix + "\tat " + trace[i]);
600 if (framesInCommon != 0)
601 s.println(prefix + "\t... " + framesInCommon + " more");
602
603 // Print suppressed exceptions, if any
604 for (Throwable se : suppressedExceptions)
605 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
606 prefix +"\t", dejaVu);
607
608 // Print cause, if any
609 Throwable ourCause = getCause();
610 if (ourCause != null)
611 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
612 }
613 }
614
615 /**
616 * Prints this throwable and its backtrace to the specified
617 * print writer.
618 *
619 * @param s <code>PrintWriter</code> to use for output
620 * @since JDK1.1
621 */
622 public void printStackTrace(PrintWriter s) {
623 printStackTrace(new WrappedPrintWriter(s));
624 }
625
626 /**
627 * Wrapper class for PrintStream and PrintWriter to enable a single
628 * implementation of printStackTrace.
629 */
630 private abstract static class PrintStreamOrWriter {
631 /** Returns the object to be locked when using this StreamOrWriter */
632 abstract Object lock();
633
634 /** Prints the specified string as a line on this StreamOrWriter */
635 abstract void println(Object o);
636 }
637
638 private static class WrappedPrintStream extends PrintStreamOrWriter {
639 private final PrintStream printStream;
652 }
653
654 private static class WrappedPrintWriter extends PrintStreamOrWriter {
655 private final PrintWriter printWriter;
656
657 WrappedPrintWriter(PrintWriter printWriter) {
658 this.printWriter = printWriter;
659 }
660
661 Object lock() {
662 return printWriter;
663 }
664
665 void println(Object o) {
666 printWriter.println(o);
667 }
668 }
669
670 /**
671 * Fills in the execution stack trace. This method records within this
672 * <code>Throwable</code> object information about the current state of
673 * the stack frames for the current thread.
674 *
675 * @return a reference to this <code>Throwable</code> instance.
676 * @see java.lang.Throwable#printStackTrace()
677 */
678 public synchronized native Throwable fillInStackTrace();
679
680 /**
681 * Provides programmatic access to the stack trace information printed by
682 * {@link #printStackTrace()}. Returns an array of stack trace elements,
683 * each representing one stack frame. The zeroth element of the array
684 * (assuming the array's length is non-zero) represents the top of the
685 * stack, which is the last method invocation in the sequence. Typically,
686 * this is the point at which this throwable was created and thrown.
687 * The last element of the array (assuming the array's length is non-zero)
688 * represents the bottom of the stack, which is the first method invocation
689 * in the sequence.
690 *
691 * <p>Some virtual machines may, under some circumstances, omit one
692 * or more stack frames from the stack trace. In the extreme case,
693 * a virtual machine that has no stack trace information concerning
694 * this throwable is permitted to return a zero-length array from this
695 * method. Generally speaking, the array returned by this method will
696 * contain one element for every frame that would be printed by
697 * <tt>printStackTrace</tt>.
698 *
699 * @return an array of stack trace elements representing the stack trace
700 * pertaining to this throwable.
701 * @since 1.4
702 */
703 public StackTraceElement[] getStackTrace() {
704 return getOurStackTrace().clone();
705 }
706
707 private synchronized StackTraceElement[] getOurStackTrace() {
708 // Initialize stack trace if this is the first call to this method
709 if (stackTrace == null) {
710 int depth = getStackTraceDepth();
711 stackTrace = new StackTraceElement[depth];
712 for (int i=0; i < depth; i++)
713 stackTrace[i] = getStackTraceElement(i);
714 }
715 return stackTrace;
716 }
717
718 /**
719 * Sets the stack trace elements that will be returned by
720 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
721 * and related methods.
722 *
723 * This method, which is designed for use by RPC frameworks and other
724 * advanced systems, allows the client to override the default
725 * stack trace that is either generated by {@link #fillInStackTrace()}
726 * when a throwable is constructed or deserialized when a throwable is
727 * read from a serialization stream.
728 *
729 * @param stackTrace the stack trace elements to be associated with
730 * this <code>Throwable</code>. The specified array is copied by this
731 * call; changes in the specified array after the method invocation
732 * returns will have no affect on this <code>Throwable</code>'s stack
733 * trace.
734 *
735 * @throws NullPointerException if <code>stackTrace</code> is
736 * <code>null</code>, or if any of the elements of
737 * <code>stackTrace</code> are <code>null</code>
738 *
739 * @since 1.4
740 */
741 public void setStackTrace(StackTraceElement[] stackTrace) {
742 StackTraceElement[] defensiveCopy = stackTrace.clone();
743 for (int i = 0; i < defensiveCopy.length; i++)
744 if (defensiveCopy[i] == null)
745 throw new NullPointerException("stackTrace[" + i + "]");
746
747 this.stackTrace = defensiveCopy;
748 }
749
750 /**
751 * Returns the number of elements in the stack trace (or 0 if the stack
752 * trace is unavailable).
753 *
754 * package-protection for use by SharedSecrets.
755 */
756 native int getStackTraceDepth();
757
758 /**
759 * Returns the specified element of the stack trace.
760 *
761 * package-protection for use by SharedSecrets.
762 *
763 * @param index index of the element to return.
764 * @throws IndexOutOfBoundsException if <tt>index < 0 ||
765 * index >= getStackTraceDepth() </tt>
766 */
767 native StackTraceElement getStackTraceElement(int index);
768
769 private void readObject(ObjectInputStream s)
770 throws IOException, ClassNotFoundException {
771 s.defaultReadObject(); // read in all fields
772 List<Throwable> suppressed = Collections.emptyList();
773 if (suppressedExceptions != null &&
774 !suppressedExceptions.isEmpty()) { // Copy Throwables to new list
775 suppressed = new ArrayList<Throwable>();
776 for(Throwable t : suppressedExceptions) {
777 if (t == null)
778 throw new NullPointerException(NULL_CAUSE_MESSAGE);
779 suppressed.add(t);
780 }
781 }
782 suppressedExceptions = suppressed;
783 }
784
785 private synchronized void writeObject(ObjectOutputStream s)
786 throws IOException
787 {
788 getOurStackTrace(); // Ensure that stackTrace field is initialized.
789 s.defaultWriteObject();
790 }
791
792 /**
793 * Adds the specified exception to the list of exceptions that
794 * were suppressed, typically by the automatic resource management
795 * statement, in order to deliver this exception.
796 *
797 * @param exception the exception to be added to the list of
798 * suppressed exceptions
799 * @throws NullPointerException if {@code exception} is null
800 * @since 1.7
801 */
802 public synchronized void addSuppressedException(Throwable exception) {
803 if (exception == null)
804 throw new NullPointerException(NULL_CAUSE_MESSAGE);
805
806 if (suppressedExceptions.size() == 0)
807 suppressedExceptions = new ArrayList<Throwable>();
808 suppressedExceptions.add(exception);
809 }
810
811 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
812
813 /**
814 * Returns an array containing all of the exceptions that were
815 * suppressed, typically by the automatic resource management
816 * statement, in order to deliver this exception.
817 *
818 * @return an array containing all of the exceptions that were
819 * suppressed to deliver this exception.
820 * @since 1.7
821 */
822 public Throwable[] getSuppressedExceptions() {
823 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
824 }
|
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()}.
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 = Collections.emptyList();
204
205 /** Message for trying to suppress a null exception. */
206 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
207
208 /** Caption for labeling causative exception stack traces */
209 private static final String CAUSE_CAPTION = "Caused by: ";
210
211 /** Caption for labeling suppressed exception stack traces */
212 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
213
214 /**
215 * Constructs a new throwable with {@code null} as its detail message.
216 * The cause is not initialized, and may subsequently be initialized by a
217 * call to {@link #initCause}.
218 *
219 * <p>The {@link #fillInStackTrace()} method is called to initialize
220 * the stack trace data in the newly created throwable.
221 */
222 public Throwable() {
223 fillInStackTrace();
224 }
225
226 /**
227 * Constructs a new throwable with the specified detail message. The
228 * cause is not initialized, and may subsequently be initialized by
229 * a call to {@link #initCause}.
230 *
231 * <p>The {@link #fillInStackTrace()} method is called to initialize
232 * the stack trace data in the newly created throwable.
233 *
234 * @param message the detail message. The detail message is saved for
235 * later retrieval by the {@link #getMessage()} method.
236 */
237 public Throwable(String message) {
238 fillInStackTrace();
239 detailMessage = message;
240 }
241
242 /**
243 * Constructs a new throwable with the specified detail message and
244 * cause. <p>Note that the detail message associated with
245 * {@code cause} is <i>not</i> automatically incorporated in
246 * this throwable's detail message.
247 *
248 * <p>The {@link #fillInStackTrace()} method is called to initialize
249 * the stack trace data in the newly created throwable.
250 *
251 * @param message the detail message (which is saved for later retrieval
252 * by the {@link #getMessage()} method).
253 * @param cause the cause (which is saved for later retrieval by the
254 * {@link #getCause()} method). (A {@code null} value is
255 * permitted, and indicates that the cause is nonexistent or
256 * unknown.)
257 * @since 1.4
258 */
259 public Throwable(String message, Throwable cause) {
260 fillInStackTrace();
261 detailMessage = message;
262 this.cause = cause;
263 }
264
265 /**
266 * Constructs a new throwable with the specified cause and a detail
267 * message of {@code (cause==null ? null : cause.toString())} (which
268 * typically contains the class and detail message of {@code cause}).
269 * This constructor is useful for throwables that are little more than
270 * wrappers for other throwables (for example, {@link
271 * java.security.PrivilegedActionException}).
272 *
273 * <p>The {@link #fillInStackTrace()} method is called to initialize
274 * the stack trace data in the newly created throwable.
275 *
276 * @param cause the cause (which is saved for later retrieval by the
277 * {@link #getCause()} method). (A {@code null} value is
278 * permitted, and indicates that the cause is nonexistent or
279 * unknown.)
280 * @since 1.4
281 */
282 public Throwable(Throwable cause) {
283 fillInStackTrace();
284 detailMessage = (cause==null ? null : cause.toString());
285 this.cause = cause;
286 }
287
288 /**
289 * Returns the detail message string of this throwable.
290 *
291 * @return the detail message string of this {@code Throwable} instance
292 * (which may be {@code null}).
293 */
294 public String getMessage() {
295 return detailMessage;
296 }
297
298 /**
299 * Creates a localized description of this throwable.
300 * Subclasses may override this method in order to produce a
301 * locale-specific message. For subclasses that do not override this
302 * method, the default implementation returns the same result as
303 * {@code getMessage()}.
304 *
305 * @return The localized description of this throwable.
306 * @since JDK1.1
307 */
308 public String getLocalizedMessage() {
309 return getMessage();
310 }
311
312 /**
313 * Returns the cause of this throwable or {@code null} if the
314 * cause is nonexistent or unknown. (The cause is the throwable that
315 * caused this throwable to get thrown.)
316 *
317 * <p>This implementation returns the cause that was supplied via one of
318 * the constructors requiring a {@code Throwable}, or that was set after
319 * creation with the {@link #initCause(Throwable)} method. While it is
320 * typically unnecessary to override this method, a subclass can override
321 * it to return a cause set by some other means. This is appropriate for
322 * a "legacy chained throwable" that predates the addition of chained
323 * exceptions to {@code Throwable}. Note that it is <i>not</i>
324 * necessary to override any of the {@code PrintStackTrace} methods,
325 * all of which invoke the {@code getCause} method to determine the
326 * cause of a throwable.
327 *
328 * @return the cause of this throwable or {@code null} if the
329 * cause is nonexistent or unknown.
330 * @since 1.4
331 */
332 public Throwable getCause() {
333 return (cause==this ? null : cause);
334 }
335
336 /**
337 * Initializes the <i>cause</i> of this throwable to the specified value.
338 * (The cause is the throwable that caused this throwable to get thrown.)
339 *
340 * <p>This method can be called at most once. It is generally called from
341 * within the constructor, or immediately after creating the
342 * throwable. If this throwable was created
343 * with {@link #Throwable(Throwable)} or
344 * {@link #Throwable(String,Throwable)}, this method cannot be called
345 * even once.
346 *
347 * @param cause the cause (which is saved for later retrieval by the
348 * {@link #getCause()} method). (A {@code null} value is
349 * permitted, and indicates that the cause is nonexistent or
350 * unknown.)
351 * @return a reference to this {@code Throwable} instance.
352 * @throws IllegalArgumentException if {@code cause} is this
353 * throwable. (A throwable cannot be its own cause.)
354 * @throws IllegalStateException if this throwable was
355 * created with {@link #Throwable(Throwable)} or
356 * {@link #Throwable(String,Throwable)}, or this method has already
357 * been called on this throwable.
358 * @since 1.4
359 */
360 public synchronized Throwable initCause(Throwable cause) {
361 if (this.cause != this)
362 throw new IllegalStateException("Can't overwrite cause");
363 if (cause == this)
364 throw new IllegalArgumentException("Self-causation not permitted");
365 this.cause = cause;
366 return this;
367 }
368
369 /**
370 * Returns a short description of this throwable.
371 * The result is the concatenation of:
372 * <ul>
373 * <li> the {@linkplain Class#getName() name} of the class of this object
374 * <li> ": " (a colon and a space)
375 * <li> the result of invoking this object's {@link #getLocalizedMessage}
376 * method
377 * </ul>
378 * If {@code getLocalizedMessage} returns {@code null}, then just
379 * the class name is returned.
380 *
381 * @return a string representation of this throwable.
382 */
383 public String toString() {
384 String s = getClass().getName();
385 String message = getLocalizedMessage();
386 return (message != null) ? (s + ": " + message) : s;
387 }
388
389 /**
390 * Prints this throwable and its backtrace to the
391 * standard error stream. This method prints a stack trace for this
392 * {@code Throwable} object on the error output stream that is
393 * the value of the field {@code System.err}. The first line of
394 * output contains the result of the {@link #toString()} method for
395 * this object. Remaining lines represent data previously recorded by
396 * the method {@link #fillInStackTrace()}. The format of this
397 * information depends on the implementation, but the following
398 * example may be regarded as typical:
399 * <blockquote><pre>
400 * java.lang.NullPointerException
401 * at MyClass.mash(MyClass.java:9)
402 * at MyClass.crunch(MyClass.java:6)
403 * at MyClass.main(MyClass.java:3)
404 * </pre></blockquote>
405 * This example was produced by running the program:
406 * <pre>
407 * class MyClass {
408 * public static void main(String[] args) {
409 * crunch(null);
410 * }
411 * static void crunch(int[] a) {
412 * mash(a);
413 * }
418 * </pre>
419 * The backtrace for a throwable with an initialized, non-null cause
420 * should generally include the backtrace for the cause. The format
421 * of this information depends on the implementation, but the following
422 * example may be regarded as typical:
423 * <pre>
424 * HighLevelException: MidLevelException: LowLevelException
425 * at Junk.a(Junk.java:13)
426 * at Junk.main(Junk.java:4)
427 * Caused by: MidLevelException: LowLevelException
428 * at Junk.c(Junk.java:23)
429 * at Junk.b(Junk.java:17)
430 * at Junk.a(Junk.java:11)
431 * ... 1 more
432 * Caused by: LowLevelException
433 * at Junk.e(Junk.java:30)
434 * at Junk.d(Junk.java:27)
435 * at Junk.c(Junk.java:21)
436 * ... 3 more
437 * </pre>
438 * Note the presence of lines containing the characters {@code "..."}.
439 * These lines indicate that the remainder of the stack trace for this
440 * exception matches the indicated number of frames from the bottom of the
441 * stack trace of the exception that was caused by this exception (the
442 * "enclosing" exception). This shorthand can greatly reduce the length
443 * of the output in the common case where a wrapped exception is thrown
444 * from same method as the "causative exception" is caught. The above
445 * example was produced by running the program:
446 * <pre>
447 * public class Junk {
448 * public static void main(String args[]) {
449 * try {
450 * a();
451 * } catch(HighLevelException e) {
452 * e.printStackTrace();
453 * }
454 * }
455 * static void a() throws HighLevelException {
456 * try {
457 * b();
458 * } catch(MidLevelException e) {
525 * </pre>
526 * Likewise, a suppressed exception can have a cause:
527 * <pre>
528 * Exception in thread "main" java.lang.Exception: Main block
529 * at Foo4.main(Foo4.java:6)
530 * Suppressed: Resource2$CloseFailException: Resource ID = 1
531 * at Resource2.close(Resource2.java:20)
532 * at Foo4.main(Foo4.java:5)
533 * Caused by: java.lang.Exception: Rats, you caught me
534 * at Resource2$CloseFailException.<init>(Resource2.java:45)
535 * ... 2 more
536 * </pre>
537 */
538 public void printStackTrace() {
539 printStackTrace(System.err);
540 }
541
542 /**
543 * Prints this throwable and its backtrace to the specified print stream.
544 *
545 * @param s {@code PrintStream} to use for output
546 */
547 public void printStackTrace(PrintStream s) {
548 printStackTrace(new WrappedPrintStream(s));
549 }
550
551 private void printStackTrace(PrintStreamOrWriter s) {
552 // Guard against malicious overrides of Throwable.equals by
553 // using a Set with identity equality semantics.
554 Set<Throwable> dejaVu =
555 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
556 dejaVu.add(this);
557
558 synchronized (s.lock()) {
559 // Print our stack trace
560 s.println(this);
561 StackTraceElement[] trace = getOurStackTrace();
562 for (StackTraceElement traceElement : trace)
563 s.println("\tat " + traceElement);
564
565 // Print suppressed exceptions, if any
566 for (Throwable se : suppressedExceptions)
567 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
568
569 // Print cause, if any
570 Throwable ourCause = getCause();
571 if (ourCause != null)
572 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
573 }
574 }
575
602 s.println(prefix + "\tat " + trace[i]);
603 if (framesInCommon != 0)
604 s.println(prefix + "\t... " + framesInCommon + " more");
605
606 // Print suppressed exceptions, if any
607 for (Throwable se : suppressedExceptions)
608 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
609 prefix +"\t", dejaVu);
610
611 // Print cause, if any
612 Throwable ourCause = getCause();
613 if (ourCause != null)
614 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
615 }
616 }
617
618 /**
619 * Prints this throwable and its backtrace to the specified
620 * print writer.
621 *
622 * @param s {@code PrintWriter} to use for output
623 * @since JDK1.1
624 */
625 public void printStackTrace(PrintWriter s) {
626 printStackTrace(new WrappedPrintWriter(s));
627 }
628
629 /**
630 * Wrapper class for PrintStream and PrintWriter to enable a single
631 * implementation of printStackTrace.
632 */
633 private abstract static class PrintStreamOrWriter {
634 /** Returns the object to be locked when using this StreamOrWriter */
635 abstract Object lock();
636
637 /** Prints the specified string as a line on this StreamOrWriter */
638 abstract void println(Object o);
639 }
640
641 private static class WrappedPrintStream extends PrintStreamOrWriter {
642 private final PrintStream printStream;
655 }
656
657 private static class WrappedPrintWriter extends PrintStreamOrWriter {
658 private final PrintWriter printWriter;
659
660 WrappedPrintWriter(PrintWriter printWriter) {
661 this.printWriter = printWriter;
662 }
663
664 Object lock() {
665 return printWriter;
666 }
667
668 void println(Object o) {
669 printWriter.println(o);
670 }
671 }
672
673 /**
674 * Fills in the execution stack trace. This method records within this
675 * {@code Throwable} object information about the current state of
676 * the stack frames for the current thread.
677 *
678 * @return a reference to this {@code Throwable} instance.
679 * @see java.lang.Throwable#printStackTrace()
680 */
681 public synchronized native Throwable fillInStackTrace();
682
683 /**
684 * Provides programmatic access to the stack trace information printed by
685 * {@link #printStackTrace()}. Returns an array of stack trace elements,
686 * each representing one stack frame. The zeroth element of the array
687 * (assuming the array's length is non-zero) represents the top of the
688 * stack, which is the last method invocation in the sequence. Typically,
689 * this is the point at which this throwable was created and thrown.
690 * The last element of the array (assuming the array's length is non-zero)
691 * represents the bottom of the stack, which is the first method invocation
692 * in the sequence.
693 *
694 * <p>Some virtual machines may, under some circumstances, omit one
695 * or more stack frames from the stack trace. In the extreme case,
696 * a virtual machine that has no stack trace information concerning
697 * this throwable is permitted to return a zero-length array from this
698 * method. Generally speaking, the array returned by this method will
699 * contain one element for every frame that would be printed by
700 * {@code printStackTrace}.
701 *
702 * @return an array of stack trace elements representing the stack trace
703 * pertaining to this throwable.
704 * @since 1.4
705 */
706 public StackTraceElement[] getStackTrace() {
707 return getOurStackTrace().clone();
708 }
709
710 private synchronized StackTraceElement[] getOurStackTrace() {
711 // Initialize stack trace if this is the first call to this method
712 if (stackTrace == null) {
713 int depth = getStackTraceDepth();
714 stackTrace = new StackTraceElement[depth];
715 for (int i=0; i < depth; i++)
716 stackTrace[i] = getStackTraceElement(i);
717 }
718 return stackTrace;
719 }
720
721 /**
722 * Sets the stack trace elements that will be returned by
723 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
724 * and related methods.
725 *
726 * This method, which is designed for use by RPC frameworks and other
727 * advanced systems, allows the client to override the default
728 * stack trace that is either generated by {@link #fillInStackTrace()}
729 * when a throwable is constructed or deserialized when a throwable is
730 * read from a serialization stream.
731 *
732 * @param stackTrace the stack trace elements to be associated with
733 * this {@code Throwable}. The specified array is copied by this
734 * call; changes in the specified array after the method invocation
735 * returns will have no affect on this {@code Throwable}'s stack
736 * trace.
737 *
738 * @throws NullPointerException if {@code stackTrace} is
739 * {@code null}, or if any of the elements of
740 * {@code stackTrace} are {@code null}
741 *
742 * @since 1.4
743 */
744 public void setStackTrace(StackTraceElement[] stackTrace) {
745 StackTraceElement[] defensiveCopy = stackTrace.clone();
746 for (int i = 0; i < defensiveCopy.length; i++)
747 if (defensiveCopy[i] == null)
748 throw new NullPointerException("stackTrace[" + i + "]");
749
750 this.stackTrace = defensiveCopy;
751 }
752
753 /**
754 * Returns the number of elements in the stack trace (or 0 if the stack
755 * trace is unavailable).
756 *
757 * package-protection for use by SharedSecrets.
758 */
759 native int getStackTraceDepth();
760
761 /**
762 * Returns the specified element of the stack trace.
763 *
764 * package-protection for use by SharedSecrets.
765 *
766 * @param index index of the element to return.
767 * @throws IndexOutOfBoundsException if {@code index < 0 ||
768 * index >= getStackTraceDepth() }
769 */
770 native StackTraceElement getStackTraceElement(int index);
771
772 private void readObject(ObjectInputStream s)
773 throws IOException, ClassNotFoundException {
774 s.defaultReadObject(); // read in all fields
775 List<Throwable> suppressed = Collections.emptyList();
776 if (suppressedExceptions != null &&
777 !suppressedExceptions.isEmpty()) { // Copy Throwables to new list
778 suppressed = new ArrayList<Throwable>();
779 for(Throwable t : suppressedExceptions) {
780 if (t == null)
781 throw new NullPointerException(NULL_CAUSE_MESSAGE);
782 suppressed.add(t);
783 }
784 }
785 suppressedExceptions = suppressed;
786 }
787
788 private synchronized void writeObject(ObjectOutputStream s)
789 throws IOException
790 {
791 getOurStackTrace(); // Ensure that stackTrace field is initialized.
792 s.defaultWriteObject();
793 }
794
795 /**
796 * Adds the specified exception to the list of exceptions that
797 * were suppressed, typically by the automatic resource management
798 * statement, in order to deliver this exception.
799 *
800 * <p>Note that when one exception {@linkplain
801 * #initCause(Throwable) causes} another exception, the first
802 * exception is usually caught and then the second exception is
803 * thrown in response. In contrast, when when one exception
804 * suppresses another, two exceptions are thrown in sibling code
805 * blocks, such as in a {@code try} block and in its {@code
806 * finally} block, and control flow can only continue with one
807 * exception so the second is recorded as a suppressed exception
808 * of the first.
809 *
810 * @param exception the exception to be added to the list of
811 * suppressed exceptions
812 * @throws NullPointerException if {@code exception} is null
813 * @throws IllegalArgumentException if {@code exception} is this
814 * throwable; a throwable cannot suppress itself.
815 * @since 1.7
816 */
817 public synchronized void addSuppressedException(Throwable exception) {
818 if (exception == null)
819 throw new NullPointerException(NULL_CAUSE_MESSAGE);
820 if (exception == this)
821 throw new IllegalArgumentException("Self-suppression not permitted");
822
823 if (suppressedExceptions.size() == 0)
824 suppressedExceptions = new ArrayList<Throwable>();
825 suppressedExceptions.add(exception);
826 }
827
828 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
829
830 /**
831 * Returns an array containing all of the exceptions that were
832 * suppressed, typically by the automatic resource management
833 * statement, in order to deliver this exception.
834 *
835 * @return an array containing all of the exceptions that were
836 * suppressed to deliver this exception.
837 * @since 1.7
838 */
839 public Throwable[] getSuppressedExceptions() {
840 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
841 }
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