Throwable


1   /*
2    * @(#)Throwable.java   1.53 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.lang;
9   import  java.io.*;
10  
11  /**
12   * The <code>Throwable</code> class is the superclass of all errors and
13   * exceptions in the Java language. Only objects that are instances of this
14   * class (or one of its subclasses) are thrown by the Java Virtual Machine or
15   * can be thrown by the Java <code>throw</code> statement. Similarly, only
16   * this class or one of its subclasses can be the argument type in a
17   * <code>catch</code> clause.
18   * 
19   * <p>Instances of two subclasses, {@link java.lang.Error} and 
20   * {@link java.lang.Exception}, are conventionally used to indicate 
21   * that exceptional situations have occurred. Typically, these instances 
22   * are freshly created in the context of the exceptional situation so 
23   * as to include relevant information (such as stack trace data).
24   * 
25   * <p>A throwable contains a snapshot of the execution stack of its thread at
26   * the time it was created. It can also contain a message string that gives
27   * more information about the error. Finally, it can contain a <i>cause</i>:
28   * another throwable that caused this throwable to get thrown.  The cause
29   * facility is new in release 1.4.  It is also known as the <i>chained
30   * exception</i> facility, as the cause can, itself, have a cause, and so on,
31   * leading to a "chain" of exceptions, each caused by another.
32   *
33   * <p>One reason that a throwable may have a cause is that the class that
34   * throws it is built atop a lower layered abstraction, and an operation on
35   * the upper layer fails due to a failure in the lower layer.  It would be bad
36   * design to let the throwable thrown by the lower layer propagate outward, as
37   * it is generally unrelated to the abstraction provided by the upper layer.
38   * Further, doing so would tie the API of the upper layer to the details of
39   * its implementation, assuming the lower layer's exception was a checked
40   * exception.  Throwing a "wrapped exception" (i.e., an exception containing a
41   * cause) allows the upper layer to communicate the details of the failure to
42   * its caller without incurring either of these shortcomings.  It preserves
43   * the flexibility to change the implementation of the upper layer without
44   * changing its API (in particular, the set of exceptions thrown by its
45   * methods).
46   *
47   * <p>A second reason that a throwable may have a cause is that the method
48   * that throws it must conform to a general-purpose interface that does not
49   * permit the method to throw the cause directly.  For example, suppose
50   * a persistent collection conforms to the {@link java.util.Collection
51   * Collection} interface, and that its persistence is implemented atop
52   * <tt>java.io</tt>.  Suppose the internals of the <tt>put</tt> method 
53   * can throw an {@link java.io.IOException IOException}.  The implementation
54   * can communicate the details of the <tt>IOException</tt> to its caller
55   * while conforming to the <tt>Collection</tt> interface by wrapping the
56   * <tt>IOException</tt> in an appropriate unchecked exception.  (The
57   * specification for the persistent collection should indicate that it is
58   * capable of throwing such exceptions.)
59   *
60   * <p>A cause can be associated with a throwable in two ways: via a
61   * constructor that takes the cause as an argument, or via the
62   * {@link #initCause(Throwable)} method.  New throwable classes that
63   * wish to allow causes to be associated with them should provide constructors
64   * that take a cause and delegate (perhaps indirectly) to one of the
65   * <tt>Throwable</tt> constructors that takes a cause.  For example:
66   * <pre>
67   *     try {
68   *         lowLevelOp();
69   *     } catch (LowLevelException le) {
70   *         throw new HighLevelException(le);  // Chaining-aware constructor
71   *     }
72   * </pre>
73   * Because the <tt>initCause</tt> method is public, it allows a cause to be
74   * associated with any throwable, even a "legacy throwable" whose
75   * implementation predates the addition of the exception chaining mechanism to
76   * <tt>Throwable</tt>. For example:
77   * <pre>
78   *     try {
79   *         lowLevelOp();
80   *     } catch (LowLevelException le) {
81   *         throw (HighLevelException)
82                   new HighLevelException().initCause(le);  // Legacy constructor
83   *     }
84   * </pre>
85   *
86   * <p>Prior to release 1.4, there were many throwables that had their own
87   * non-standard exception chaining mechanisms (
88   * {@link ExceptionInInitializerError}, {@link ClassNotFoundException},
89   * {@link java.lang.reflect.UndeclaredThrowableException},
90   * {@link java.lang.reflect.InvocationTargetException}, 
91   * {@link java.io.WriteAbortedException},
92   * {@link java.security.PrivilegedActionException},
93   * {@link java.awt.print.PrinterIOException},
94   * {@link java.rmi.RemoteException} and
95   * {@link javax.naming.NamingException}).
96   * All of these throwables have been retrofitted to 
97   * use the standard exception chaining mechanism, while continuing to
98   * implement their "legacy" chaining mechanisms for compatibility.
99   *
100  * <p>Further, as of release 1.4, many general purpose <tt>Throwable</tt>
101  * classes (for example {@link Exception}, {@link RuntimeException},
102  * {@link Error}) have been retrofitted with constructors that take
103  * a cause.  This was not strictly necessary, due to the existence of the
104  * <tt>initCause</tt> method, but it is more convenient and expressive to
105  * delegate to a constructor that takes a cause.
106  * 
107  * <p>By convention, class <code>Throwable</code> and its subclasses have two
108  * constructors, one that takes no arguments and one that takes a
109  * <code>String</code> argument that can be used to produce a detail message.
110  * Further, those subclasses that might likely have a cause associated with
111  * them should have two more constructors, one that takes a
112  * <code>Throwable</code> (the cause), and one that takes a
113  * <code>String</code> (the detail message) and a <code>Throwable</code> (the
114  * cause).
115  *
116  * <p>Also introduced in release 1.4 is the {@link #getStackTrace()} method,
117  * which allows programmatic access to the stack trace information that was
118  * previously available only in text form, via the various forms of the
119  * {@link #printStackTrace()} method.  This information has been added to the
120  * <i>serialized representation</i> of this class so <tt>getStackTrace</tt>
121  * and <tt>printStackTrace</tt> will operate properly on a throwable that
122  * was obtained by deserialization.
123  *
124  * @author  unascribed
125  * @author  Josh Bloch (Added exception chaining and programmatic access to
126  *          stack trace in 1.4.)
127  * @version 1.53, 12/19/03
128  * @since JDK1.0
129  */
130 public class Throwable implements Serializable {
131     /** use serialVersionUID from JDK 1.0.2 for interoperability */
132     private static final long serialVersionUID = -3042686055658047285L;
133 
134     /**
135      * Native code saves some indication of the stack backtrace in this slot.
136      */
137     private transient Object   backtrace; 
138 
139     /**
140      * Specific details about the Throwable.  For example, for
141      * <tt>FileNotFoundException</tt>, this contains the name of
142      * the file that could not be found.
143      *
144      * @serial
145      */
146     private String   detailMessage;
147 
148     /**
149      * The throwable that caused this throwable to get thrown, or null if this
150      * throwable was not caused by another throwable, or if the causative
151      * throwable is unknown.  If this field is equal to this throwable itself,
152      * it indicates that the cause of this throwable has not yet been
153      * initialized.
154      *
155      * @serial
156      * @since 1.4
157      */
158     private Throwable   cause = this;
159 
160     /**
161      * The stack trace, as returned by {@link #getStackTrace()}.
162      *
163      * @serial
164      * @since 1.4
165      */
166     private StackTraceElement  [] stackTrace;
167     /*
168      * This field is lazily initialized on first use or serialization and
169      * nulled out when fillInStackTrace is called.
170      */
171 
172     /**
173      * Constructs a new throwable with <code>null</code> as its detail message.
174      * The cause is not initialized, and may subsequently be initialized by a
175      * call to {@link #initCause}.
176      *
177      * <p>The {@link #fillInStackTrace()} method is called to initialize
178      * the stack trace data in the newly created throwable.
179      */
180     public Throwable() {
181         fillInStackTrace();
182     }
183 
184     /**
185      * Constructs a new throwable with the specified detail message.  The
186      * cause is not initialized, and may subsequently be initialized by
187      * a call to {@link #initCause}.
188      *
189      * <p>The {@link #fillInStackTrace()} method is called to initialize
190      * the stack trace data in the newly created throwable.
191      *
192      * @param   message   the detail message. The detail message is saved for 
193      *          later retrieval by the {@link #getMessage()} method.
194      */
195     public Throwable(String   message) {
196         fillInStackTrace();
197         detailMessage = message;
198     }
199 
200     /**
201      * Constructs a new throwable with the specified detail message and
202      * cause.  <p>Note that the detail message associated with
203      * <code>cause</code> is <i>not</i> automatically incorporated in
204      * this throwable's detail message.
205      *
206      * <p>The {@link #fillInStackTrace()} method is called to initialize
207      * the stack trace data in the newly created throwable.
208      *
209      * @param  message the detail message (which is saved for later retrieval
210      *         by the {@link #getMessage()} method).
211      * @param  cause the cause (which is saved for later retrieval by the
212      *         {@link #getCause()} method).  (A <tt>null</tt> value is
213      *         permitted, and indicates that the cause is nonexistent or
214      *         unknown.)
215      * @since  1.4
216      */
217     public Throwable(String   message, Throwable   cause) {
218         fillInStackTrace();
219         detailMessage = message;
220         this.cause = cause;
221     }
222 
223     /**
224      * Constructs a new throwable with the specified cause and a detail
225      * message of <tt>(cause==null ? null : cause.toString())</tt> (which
226      * typically contains the class and detail message of <tt>cause</tt>).
227      * This constructor is useful for throwables that are little more than
228      * wrappers for other throwables (for example, {@link
229      * java.security.PrivilegedActionException}).
230      *
231      * <p>The {@link #fillInStackTrace()} method is called to initialize
232      * the stack trace data in the newly created throwable.
233      *
234      * @param  cause the cause (which is saved for later retrieval by the
235      *         {@link #getCause()} method).  (A <tt>null</tt> value is
236      *         permitted, and indicates that the cause is nonexistent or
237      *         unknown.)
238      * @since  1.4
239      */
240     public Throwable(Throwable   cause) {
241         fillInStackTrace();
242         detailMessage = (cause==null ? null : cause.toString());
243         this.cause = cause;
244     }
245 
246     /**
247      * Returns the detail message string of this throwable.
248      *
249      * @return  the detail message string of this <tt>Throwable</tt> instance
250      *          (which may be <tt>null</tt>).
251      */
252     public String   getMessage() {
253         return detailMessage;
254     }
255 
256     /**
257      * Creates a localized description of this throwable.
258      * Subclasses may override this method in order to produce a
259      * locale-specific message.  For subclasses that do not override this
260      * method, the default implementation returns the same result as
261      * <code>getMessage()</code>.
262      *
263      * @return  The localized description of this throwable.
264      * @since   JDK1.1
265      */
266     public String   getLocalizedMessage() {
267         return getMessage();
268     }
269 
270     /**
271      * Returns the cause of this throwable or <code>null</code> if the
272      * cause is nonexistent or unknown.  (The cause is the throwable that
273      * caused this throwable to get thrown.)
274      *
275      * <p>This implementation returns the cause that was supplied via one of
276      * the constructors requiring a <tt>Throwable</tt>, or that was set after
277      * creation with the {@link #initCause(Throwable)} method.  While it is
278      * typically unnecessary to override this method, a subclass can override
279      * it to return a cause set by some other means.  This is appropriate for
280      * a "legacy chained throwable" that predates the addition of chained
281      * exceptions to <tt>Throwable</tt>.  Note that it is <i>not</i>
282      * necessary to override any of the <tt>PrintStackTrace</tt> methods,
283      * all of which invoke the <tt>getCause</tt> method to determine the
284      * cause of a throwable.
285      *
286      * @return  the cause of this throwable or <code>null</code> if the
287      *          cause is nonexistent or unknown.
288      * @since 1.4
289      */
290     public Throwable   getCause() {
291         return (cause==this ? null : cause);
292     }
293 
294     /**
295      * Initializes the <i>cause</i> of this throwable to the specified value.
296      * (The cause is the throwable that caused this throwable to get thrown.) 
297      *
298      * <p>This method can be called at most once.  It is generally called from 
299      * within the constructor, or immediately after creating the
300      * throwable.  If this throwable was created
301      * with {@link #Throwable(Throwable)} or
302      * {@link #Throwable(String,Throwable)}, this method cannot be called
303      * even once.
304      *
305      * @param  cause the cause (which is saved for later retrieval by the
306      *         {@link #getCause()} method).  (A <tt>null</tt> value is
307      *         permitted, and indicates that the cause is nonexistent or
308      *         unknown.)
309      * @return  a reference to this <code>Throwable</code> instance.
310      * @throws IllegalArgumentException if <code>cause</code> is this
311      *         throwable.  (A throwable cannot be its own cause.)
312      * @throws IllegalStateException if this throwable was
313      *         created with {@link #Throwable(Throwable)} or
314      *         {@link #Throwable(String,Throwable)}, or this method has already
315      *         been called on this throwable.
316      * @since  1.4
317      */
318     public synchronized Throwable   initCause(Throwable   cause) {
319         if (this.cause != this)
320             throw new IllegalStateException  ("Can't overwrite cause");
321         if (cause == this)
322             throw new IllegalArgumentException  ("Self-causation not permitted");
323         this.cause = cause;
324         return this;
325     }
326 
327     /**
328      * Returns a short description of this throwable.
329      * If this <code>Throwable</code> object was created with a non-null detail
330      * message string, then the result is the concatenation of three strings: 
331      * <ul>
332      * <li>The name of the actual class of this object 
333      * <li>": " (a colon and a space)
334      * <li>The result of the {@link #getMessage} method for this object 
335      * </ul>
336      * If this <code>Throwable</code> object was created with a <tt>null</tt>
337      * detail message string, then the name of the actual class of this object
338      * is returned. 
339      *
340      * @return a string representation of this throwable.
341      */
342     public String   toString() {
343         String   s = getClass().getName();
344         String   message = getLocalizedMessage();
345         return (message != null) ? (s + ": " + message) : s;
346     }
347 
348     /**
349      * Prints this throwable and its backtrace to the 
350      * standard error stream. This method prints a stack trace for this 
351      * <code>Throwable</code> object on the error output stream that is 
352      * the value of the field <code>System.err</code>. The first line of 
353      * output contains the result of the {@link #toString()} method for 
354      * this object.  Remaining lines represent data previously recorded by 
355      * the method {@link #fillInStackTrace()}. The format of this 
356      * information depends on the implementation, but the following 
357      * example may be regarded as typical: 
358      * <blockquote><pre>
359      * java.lang.NullPointerException
360      *         at MyClass.mash(MyClass.java:9)
361      *         at MyClass.crunch(MyClass.java:6)
362      *         at MyClass.main(MyClass.java:3)
363      * </pre></blockquote>
364      * This example was produced by running the program: 
365      * <pre>
366      * class MyClass {
367      *     public static void main(String[] args) {
368      *         crunch(null);
369      *     }
370      *     static void crunch(int[] a) {
371      *         mash(a);
372      *     }
373      *     static void mash(int[] b) {
374      *         System.out.println(b[0]);
375      *     }
376      * }
377      * </pre>
378      * The backtrace for a throwable with an initialized, non-null cause
379      * should generally include the backtrace for the cause.  The format
380      * of this information depends on the implementation, but the following
381      * example may be regarded as typical:
382      * <pre>
383      * HighLevelException: MidLevelException: LowLevelException
384      *         at Junk.a(Junk.java:13)
385      *         at Junk.main(Junk.java:4)
386      * Caused by: MidLevelException: LowLevelException
387      *         at Junk.c(Junk.java:23)
388      *         at Junk.b(Junk.java:17)
389      *         at Junk.a(Junk.java:11)
390      *         ... 1 more
391      * Caused by: LowLevelException
392      *         at Junk.e(Junk.java:30)
393      *         at Junk.d(Junk.java:27)
394      *         at Junk.c(Junk.java:21)
395      *         ... 3 more
396      * </pre>
397      * Note the presence of lines containing the characters <tt>"..."</tt>.
398      * These lines indicate that the remainder of the stack trace for this
399      * exception matches the indicated number of frames from the bottom of the
400      * stack trace of the exception that was caused by this exception (the
401      * "enclosing" exception).  This shorthand can greatly reduce the length
402      * of the output in the common case where a wrapped exception is thrown
403      * from same method as the "causative exception" is caught.  The above
404      * example was produced by running the program:
405      * <pre>
406      * public class Junk {
407      *     public static void main(String args[]) { 
408      *         try {
409      *             a();
410      *         } catch(HighLevelException e) {
411      *             e.printStackTrace();
412      *         }
413      *     }
414      *     static void a() throws HighLevelException {
415      *         try {
416      *             b();
417      *         } catch(MidLevelException e) {
418      *             throw new HighLevelException(e);
419      *         }
420      *     }
421      *     static void b() throws MidLevelException {
422      *         c();
423      *     }   
424      *     static void c() throws MidLevelException {
425      *         try {
426      *             d();
427      *         } catch(LowLevelException e) {
428      *             throw new MidLevelException(e);
429      *         }
430      *     }
431      *     static void d() throws LowLevelException { 
432      *        e();
433      *     }
434      *     static void e() throws LowLevelException {
435      *         throw new LowLevelException();
436      *     }
437      * }
438      *
439      * class HighLevelException extends Exception {
440      *     HighLevelException(Throwable cause) { super(cause); }
441      * }
442      *
443      * class MidLevelException extends Exception {
444      *     MidLevelException(Throwable cause)  { super(cause); }
445      * }
446      * 
447      * class LowLevelException extends Exception {
448      * }
449      * </pre>
450      */
451     public void printStackTrace() { 
452         printStackTrace(System.err);
453     }
454 
455     /**
456      * Prints this throwable and its backtrace to the specified print stream.
457      *
458      * @param s <code>PrintStream</code> to use for output
459      */
460     public void printStackTrace(PrintStream s) {
461         synchronized (s) {
462             s.println(this);
463             StackTraceElement  [] trace = getOurStackTrace();
464             for (int i=0; i < trace.length; i++)
465                 s.println("\tat " + trace[i]);
466 
467             Throwable   ourCause = getCause();
468             if (ourCause != null)
469                 ourCause.printStackTraceAsCause(s, trace);
470         }
471     }
472 
473     /**
474      * Print our stack trace as a cause for the specified stack trace.
475      */
476     private void printStackTraceAsCause(PrintStream s,
477                                         StackTraceElement  [] causedTrace)
478     {
479         // assert Thread.holdsLock(s);
480 
481         // Compute number of frames in common between this and caused
482         StackTraceElement  [] trace = getOurStackTrace();
483         int m = trace.length-1, n = causedTrace.length-1;
484         while (m >= 0 && n >=0 && trace[m].equals(causedTrace[n])) {
485             m--; n--;
486         }
487         int framesInCommon = trace.length - 1 - m;
488 
489         s.println("Caused by: " + this);
490         for (int i=0; i <= m; i++)
491             s.println("\tat " + trace[i]);
492         if (framesInCommon != 0)
493             s.println("\t... " + framesInCommon + " more");
494 
495         // Recurse if we have a cause
496         Throwable   ourCause = getCause();
497         if (ourCause != null)
498             ourCause.printStackTraceAsCause(s, trace);
499     }
500 
501     /**
502      * Prints this throwable and its backtrace to the specified
503      * print writer.
504      *
505      * @param s <code>PrintWriter</code> to use for output
506      * @since   JDK1.1
507      */
508     public void printStackTrace(PrintWriter s) { 
509         synchronized (s) {
510             s.println(this);
511             StackTraceElement  [] trace = getOurStackTrace();
512             for (int i=0; i < trace.length; i++)
513                 s.println("\tat " + trace[i]);
514 
515             Throwable   ourCause = getCause();
516             if (ourCause != null)
517                 ourCause.printStackTraceAsCause(s, trace);
518         }
519     }
520 
521     /**
522      * Print our stack trace as a cause for the specified stack trace.
523      */
524     private void printStackTraceAsCause(PrintWriter s,
525                                         StackTraceElement  [] causedTrace)
526     {
527         // assert Thread.holdsLock(s);
528 
529         // Compute number of frames in common between this and caused
530         StackTraceElement  [] trace = getOurStackTrace();
531         int m = trace.length-1, n = causedTrace.length-1;
532         while (m >= 0 && n >=0 && trace[m].equals(causedTrace[n])) {
533             m--; n--;
534         }
535         int framesInCommon = trace.length - 1 - m;
536 
537         s.println("Caused by: " + this);
538         for (int i=0; i <= m; i++)
539             s.println("\tat " + trace[i]);
540         if (framesInCommon != 0)
541             s.println("\t... " + framesInCommon + " more");
542 
543         // Recurse if we have a cause
544         Throwable   ourCause = getCause();
545         if (ourCause != null)
546             ourCause.printStackTraceAsCause(s, trace);
547     }
548 
549     /**
550      * Fills in the execution stack trace. This method records within this 
551      * <code>Throwable</code> object information about the current state of 
552      * the stack frames for the current thread.
553      *
554      * @return  a reference to this <code>Throwable</code> instance.
555      * @see     java.lang.Throwable#printStackTrace()
556      */
557     public synchronized native Throwable   fillInStackTrace();
558 
559     /**
560      * Provides programmatic access to the stack trace information printed by
561      * {@link #printStackTrace()}.  Returns an array of stack trace elements,
562      * each representing one stack frame.  The zeroth element of the array
563      * (assuming the array's length is non-zero) represents the top of the
564      * stack, which is the last method invocation in the sequence.  Typically,
565      * this is the point at which this throwable was created and thrown.
566      * The last element of the array (assuming the array's length is non-zero)
567      * represents the bottom of the stack, which is the first method invocation
568      * in the sequence.
569      *
570      * <p>Some virtual machines may, under some circumstances, omit one
571      * or more stack frames from the stack trace.  In the extreme case,
572      * a virtual machine that has no stack trace information concerning
573      * this throwable is permitted to return a zero-length array from this
574      * method.  Generally speaking, the array returned by this method will
575      * contain one element for every frame that would be printed by
576      * <tt>printStackTrace</tt>.
577      *
578      * @return an array of stack trace elements representing the stack trace
579      *         pertaining to this throwable.
580      * @since  1.4
581      */
582     public StackTraceElement  [] getStackTrace() {
583         return (StackTraceElement  []) getOurStackTrace().clone();
584     }
585 
586     private synchronized StackTraceElement  [] getOurStackTrace() {
587         // Initialize stack trace if this is the first call to this method
588         if (stackTrace == null) {
589             int depth = getStackTraceDepth();
590             stackTrace = new StackTraceElement  [depth];
591             for (int i=0; i < depth; i++)
592                 stackTrace[i] = getStackTraceElement(i);
593         }
594         return stackTrace;
595     }
596 
597     /**
598      * Sets the stack trace elements that will be returned by
599      * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
600      * and related methods.
601      *
602      * This method, which is designed for use by RPC frameworks and other
603      * advanced systems, allows the client to override the default
604      * stack trace that is either generated by {@link #fillInStackTrace()}
605      * when a throwable is constructed or deserialized when a throwable is
606      * read from a serialization stream.
607      *
608      * @param   stackTrace the stack trace elements to be associated with
609      * this <code>Throwable</code>.  The specified array is copied by this
610      * call; changes in the specified array after the method invocation
611      * returns will have no affect on this <code>Throwable</code>'s stack
612      * trace.
613      *
614      * @throws NullPointerException if <code>stackTrace</code> is
615      *         <code>null</code>, or if any of the elements of
616      *         <code>stackTrace</code> are <code>null</code>
617      *
618      * @since  1.4
619      */
620     public void setStackTrace(StackTraceElement  [] stackTrace) {
621         StackTraceElement  [] defensiveCopy =
622             (StackTraceElement  []) stackTrace.clone();
623         for (int i = 0; i < defensiveCopy.length; i++)
624             if (defensiveCopy[i] == null)
625                 throw new NullPointerException  ("stackTrace[" + i + "]");
626 
627         this.stackTrace = defensiveCopy;
628     }
629 
630     /**
631      * Returns the number of elements in the stack trace (or 0 if the stack
632      * trace is unavailable).
633      */
634     private native int getStackTraceDepth();
635 
636     /**
637      * Returns the specified element of the stack trace.
638      *
639      * @param index index of the element to return.
640      * @throws IndexOutOfBoundsException if <tt>index %lt; 0 ||
641      *         index &gt;= getStackTraceDepth() </tt>
642      */
643     private native StackTraceElement   getStackTraceElement(int index);
644 
645     private synchronized void writeObject(java.io.ObjectOutputStream   s)
646         throws IOException
647     {
648         getOurStackTrace();  // Ensure that stackTrace field is initialized.
649         s.defaultWriteObject();
650     }
651 }
652
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