/*
    * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.
    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    *
    * This code is free software; you can redistribute it and/or modify it
    * under the terms of the GNU General Public License version 2 only, as
    * published by the Free Software Foundation.  Oracle designates this
    * particular file as subject to the "Classpath" exception as provided
    * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package java.lang;
  import  java.io.*;
  import  java.util.*;
  
  /**
   * The {@code Throwable} class is the superclass of all errors and
   * exceptions in the Java language. Only objects that are instances of this
   * class (or one of its subclasses) are thrown by the Java Virtual Machine or
   * can be thrown by the Java {@code throw} statement. Similarly, only
   * this class or one of its subclasses can be the argument type in a
   * {@code catch} clause.
   *
   * For the purposes of compile-time checking of exceptions, {@code
   * Throwable} and any subclass of {@code Throwable} that is not also a
   * subclass of either {@link RuntimeException} or {@link Error} are
   * regarded as checked exceptions.
   *
   * <p>Instances of two subclasses, {@link java.lang.Error} and
   * {@link java.lang.Exception}, are conventionally used to indicate
   * that exceptional situations have occurred. Typically, these instances
   * are freshly created in the context of the exceptional situation so
   * as to include relevant information (such as stack trace data).
   *
   * <p>A throwable contains a snapshot of the execution stack of its
   * thread at the time it was created. It can also contain a message
   * string that gives more information about the error. Over time, a
   * throwable can {@linkplain Throwable#addSuppressed suppress} other
   * throwables from being propagated.  Finally, the throwable can also
   * contain a <i>cause</i>: another throwable that caused this
   * throwable to be constructed.  The recording of this causal information
   * is referred to as the <i>chained exception</i> facility, as the
   * cause can, itself, have a cause, and so on, leading to a "chain" of
   * exceptions, each caused by another.
   *
   * <p>One reason that a throwable may have a cause is that the class that
   * throws it is built atop a lower layered abstraction, and an operation on
   * the upper layer fails due to a failure in the lower layer.  It would be bad
   * design to let the throwable thrown by the lower layer propagate outward, as
   * it is generally unrelated to the abstraction provided by the upper layer.
   * Further, doing so would tie the API of the upper layer to the details of
   * its implementation, assuming the lower layer's exception was a checked
   * exception.  Throwing a "wrapped exception" (i.e., an exception containing a
   * cause) allows the upper layer to communicate the details of the failure to
   * its caller without incurring either of these shortcomings.  It preserves
   * the flexibility to change the implementation of the upper layer without
   * changing its API (in particular, the set of exceptions thrown by its
   * methods).
   *
   * <p>A second reason that a throwable may have a cause is that the method
   * that throws it must conform to a general-purpose interface that does not
   * permit the method to throw the cause directly.  For example, suppose
   * a persistent collection conforms to the {@link java.util.Collection
   * Collection} interface, and that its persistence is implemented atop
   * {@code java.io}.  Suppose the internals of the {@code add} method
   * can throw an {@link java.io.IOException IOException}.  The implementation
   * can communicate the details of the {@code IOException} to its caller
   * while conforming to the {@code Collection} interface by wrapping the
   * {@code IOException} in an appropriate unchecked exception.  (The
   * specification for the persistent collection should indicate that it is
   * capable of throwing such exceptions.)
   *
   * <p>A cause can be associated with a throwable in two ways: via a
   * constructor that takes the cause as an argument, or via the
   * {@link #initCause(Throwable)} method.  New throwable classes that
   * wish to allow causes to be associated with them should provide constructors
   * that take a cause and delegate (perhaps indirectly) to one of the
   * {@code Throwable} constructors that takes a cause.
   *
   * Because the {@code initCause} method is public, it allows a cause to be
   * associated with any throwable, even a "legacy throwable" whose
   * implementation predates the addition of the exception chaining mechanism to
   * {@code Throwable}.
   *
   * <p>By convention, class {@code Throwable} and its subclasses have two
  * constructors, one that takes no arguments and one that takes a
  * {@code String} argument that can be used to produce a detail message.
  * Further, those subclasses that might likely have a cause associated with
  * them should have two more constructors, one that takes a
  * {@code Throwable} (the cause), and one that takes a
  * {@code String} (the detail message) and a {@code Throwable} (the
  * cause).
  *
  * @author  unascribed
  * @author  Josh Bloch (Added exception chaining and programmatic access to
  *          stack trace in 1.4.)
  * @jls 11.2 Compile-Time Checking of Exceptions
  * @since JDK1.0
  */
 public class Throwable implements Serializable {
     /** use serialVersionUID from JDK 1.0.2 for interoperability */
     private static final long serialVersionUID = -3042686055658047285L;
 
     /**
      * Native code saves some indication of the stack backtrace in this slot.
      */
     private transient Object backtrace;
 
     /**
      * Specific details about the Throwable.  For example, for
      * {@code FileNotFoundException}, this contains the name of
      * the file that could not be found.
      *
      * @serial
      */
     private String detailMessage;
 
 
     /**
      * Holder class to defer initializing sentinel objects only used
      * for serialization.
      */
     private static class SentinelHolder {
         /**
          * {@linkplain #setStackTrace(StackTraceElement[]) Setting the
          * stack trace} to a one-element array containing this sentinel
          * value indicates future attempts to set the stack trace will be
          * ignored.  The sentinal is equal to the result of calling:<br>
          * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)}
          */
         public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL =
             new StackTraceElement("", "", null, Integer.MIN_VALUE);
 
         /**
          * Sentinel value used in the serial form to indicate an immutable
          * stack trace.
          */
         public static final StackTraceElement[] STACK_TRACE_SENTINEL =
             new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL};
     }
 
     /**
      * A shared value for an empty stack.
      */
     private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0];
 
     /*
      * To allow Throwable objects to be made immutable and safely
      * reused by the JVM, such as OutOfMemoryErrors, fields of
      * Throwable that are writable in response to user actions, cause,
      * stackTrace, and suppressedExceptions obey the following
      * protocol:
      *
      * 1) The fields are initialized to a non-null sentinel value
      * which indicates the value has logically not been set.
      *
      * 2) Writing a null to the field indicates further writes
      * are forbidden
      *
      * 3) The sentinel value may be replaced with another non-null
      * value.
      *
      * For example, implementations of the HotSpot JVM have
      * preallocated OutOfMemoryError objects to provide for better
      * diagnosability of that situation.  These objects are created
      * without calling the constructor for that class and the fields
      * in question are initialized to null.  To support this
      * capability, any new fields added to Throwable that require
      * being initialized to a non-null value require a coordinated JVM
      * change.
      */
 
     /**
      * The throwable that caused this throwable to get thrown, or null if this
      * throwable was not caused by another throwable, or if the causative
      * throwable is unknown.  If this field is equal to this throwable itself,
      * it indicates that the cause of this throwable has not yet been
      * initialized.
      *
      * @serial
      * @since 1.4
      */
     private Throwable cause = this;
 
     /**
      * The stack trace, as returned by {@link #getStackTrace()}.
      *
      * The field is initialized to a zero-length array.  A {@code
      * null} value of this field indicates subsequent calls to {@link
      * #setStackTrace(StackTraceElement[])} and {@link
      * #fillInStackTrace()} will be be no-ops.
      *
      * @serial
      * @since 1.4
      */
     private StackTraceElement[] stackTrace = UNASSIGNED_STACK;
 
     // Setting this static field introduces an acceptable
     // initialization dependency on a few java.util classes.
     private static final List<Throwable> SUPPRESSED_SENTINEL =
         Collections.unmodifiableList(new ArrayList<Throwable>(0));
 
     /**
      * The list of suppressed exceptions, as returned by {@link
      * #getSuppressed()}.  The list is initialized to a zero-element
      * unmodifiable sentinel list.  When a serialized Throwable is
      * read in, if the {@code suppressedExceptions} field points to a
      * zero-element list, the field is reset to the sentinel value.
      *
      * @serial
      * @since 1.7
      */
     private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL;
 
     /** Message for trying to suppress a null exception. */
     private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
 
     /** Message for trying to suppress oneself. */
     private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
 
     /** Caption  for labeling causative exception stack traces */
     private static final String CAUSE_CAPTION = "Caused by: ";
 
     /** Caption for labeling suppressed exception stack traces */
     private static final String SUPPRESSED_CAPTION = "Suppressed: ";
 
     /**
      * Constructs a new throwable with {@code null} as its detail message.
      * The cause is not initialized, and may subsequently be initialized by a
      * call to {@link #initCause}.
      *
      * <p>The {@link #fillInStackTrace()} method is called to initialize
      * the stack trace data in the newly created throwable.
      */
     public Throwable() {
         fillInStackTrace();
     }
 
     /**
      * Constructs a new throwable with the specified detail message.  The
      * cause is not initialized, and may subsequently be initialized by
      * a call to {@link #initCause}.
      *
      * <p>The {@link #fillInStackTrace()} method is called to initialize
      * the stack trace data in the newly created throwable.
      *
      * @param   message   the detail message. The detail message is saved for
      *          later retrieval by the {@link #getMessage()} method.
      */
     public Throwable(String message) {
         fillInStackTrace();
         detailMessage = message;
     }
 
     /**
      * Constructs a new throwable with the specified detail message and
      * cause.  <p>Note that the detail message associated with
      * {@code cause} is <i>not</i> automatically incorporated in
      * this throwable's detail message.
      *
      * <p>The {@link #fillInStackTrace()} method is called to initialize
      * the stack trace data in the newly created throwable.
      *
      * @param  message the detail message (which is saved for later retrieval
      *         by the {@link #getMessage()} method).
      * @param  cause the cause (which is saved for later retrieval by the
      *         {@link #getCause()} method).  (A {@code null} value is
      *         permitted, and indicates that the cause is nonexistent or
      *         unknown.)
      * @since  1.4
      */
     public Throwable(String message, Throwable cause) {
         fillInStackTrace();
         detailMessage = message;
         this.cause = cause;
     }
 
     /**
      * Constructs a new throwable with the specified cause and a detail
      * message of {@code (cause==null ? null : cause.toString())} (which
      * typically contains the class and detail message of {@code cause}).
      * This constructor is useful for throwables that are little more than
      * wrappers for other throwables (for example, {@link
      * java.security.PrivilegedActionException}).
      *
      * <p>The {@link #fillInStackTrace()} method is called to initialize
      * the stack trace data in the newly created throwable.
      *
      * @param  cause the cause (which is saved for later retrieval by the
      *         {@link #getCause()} method).  (A {@code null} value is
      *         permitted, and indicates that the cause is nonexistent or
      *         unknown.)
      * @since  1.4
      */
     public Throwable(Throwable cause) {
         fillInStackTrace();
         detailMessage = (cause==null ? null : cause.toString());
         this.cause = cause;
     }
 
     /**
      * Constructs a new throwable with the specified detail message,
      * cause, {@linkplain #addSuppressed suppression} enabled or
      * disabled, and writable stack trace enabled or disabled.  If
      * suppression is disabled, {@link #getSuppressed} for this object
      * will return a zero-length array and calls to {@link
      * #addSuppressed} that would otherwise append an exception to the
      * suppressed list will have no effect.  If the writable stack
      * trace is false, this constructor will not call {@link
      * #fillInStackTrace()}, a {@code null} will be written to the
      * {@code stackTrace} field, and subsequent calls to {@code
      * fillInStackTrace} and {@link
      * #setStackTrace(StackTraceElement[])} will not set the stack
      * trace.  If the writable stack trace is false, {@link
      * #getStackTrace} will return a zero length array.
      *
      * <p>Note that the other constructors of {@code Throwable} treat
      * suppression as being enabled and the stack trace as being
      * writable.  Subclasses of {@code Throwable} should document any
      * conditions under which suppression is disabled and document
      * conditions under which the stack trace is not writable.
      * Disabling of suppression should only occur in exceptional
      * circumstances where special requirements exist, such as a
      * virtual machine reusing exception objects under low-memory
      * situations.  Circumstances where a given exception object is
      * repeatedly caught and rethrown, such as to implement control
      * flow between two sub-systems, is another situation where
      * immutable throwable objects would be appropriate.
      *
      * @param  message the detail message.
      * @param cause the cause.  (A {@code null} value is permitted,
      * and indicates that the cause is nonexistent or unknown.)
      * @param enableSuppression whether or not suppression is enabled or disabled
      * @param writableStackTrace whether or not the stack trace should be
      *                           writable
      *
      * @see OutOfMemoryError
      * @see NullPointerException
      * @see ArithmeticException
      * @since 1.7
      */
     protected Throwable(String message, Throwable cause,
                         boolean enableSuppression,
                         boolean writableStackTrace) {
         if (writableStackTrace) {
             fillInStackTrace();
         } else {
             stackTrace = null;
         }
         detailMessage = message;
         this.cause = cause;
         if (!enableSuppression)
             suppressedExceptions = null;
     }
 
     /**
      * Returns the detail message string of this throwable.
      *
      * @return  the detail message string of this {@code Throwable} instance
      *          (which may be {@code null}).
      */
     public String getMessage() {
         return detailMessage;
     }
 
     /**
      * Creates a localized description of this throwable.
      * Subclasses may override this method in order to produce a
      * locale-specific message.  For subclasses that do not override this
      * method, the default implementation returns the same result as
      * {@code getMessage()}.
      *
      * @return  The localized description of this throwable.
      * @since   JDK1.1
      */
     public String getLocalizedMessage() {
         return getMessage();
     }
 
     /**
      * Returns the cause of this throwable or {@code null} if the
      * cause is nonexistent or unknown.  (The cause is the throwable that
      * caused this throwable to get thrown.)
      *
      * <p>This implementation returns the cause that was supplied via one of
      * the constructors requiring a {@code Throwable}, or that was set after
      * creation with the {@link #initCause(Throwable)} method.  While it is
      * typically unnecessary to override this method, a subclass can override
      * it to return a cause set by some other means.  This is appropriate for
      * a "legacy chained throwable" that predates the addition of chained
      * exceptions to {@code Throwable}.  Note that it is <i>not</i>
      * necessary to override any of the {@code PrintStackTrace} methods,
      * all of which invoke the {@code getCause} method to determine the
      * cause of a throwable.
      *
      * @return  the cause of this throwable or {@code null} if the
      *          cause is nonexistent or unknown.
      * @since 1.4
      */
     public synchronized Throwable getCause() {
         return (cause==this ? null : cause);
     }
 
     /**
      * Initializes the <i>cause</i> of this throwable to the specified value.
      * (The cause is the throwable that caused this throwable to get thrown.)
      *
      * <p>This method can be called at most once.  It is generally called from
      * within the constructor, or immediately after creating the
      * throwable.  If this throwable was created
      * with {@link #Throwable(Throwable)} or
      * {@link #Throwable(String,Throwable)}, this method cannot be called
      * even once.
      *
      * <p>An example of using this method on a legacy throwable type
      * without other support for setting the cause is:
      *
      * <pre>
      * try {
      *     lowLevelOp();
      * } catch (LowLevelException le) {
      *     throw (HighLevelException)
      *           new HighLevelException().initCause(le); // Legacy constructor
      * }
      * </pre>
      *
      * @param  cause the cause (which is saved for later retrieval by the
      *         {@link #getCause()} method).  (A {@code null} value is
      *         permitted, and indicates that the cause is nonexistent or
      *         unknown.)
      * @return  a reference to this {@code Throwable} instance.
      * @throws IllegalArgumentException if {@code cause} is this
      *         throwable.  (A throwable cannot be its own cause.)
      * @throws IllegalStateException if this throwable was
      *         created with {@link #Throwable(Throwable)} or
      *         {@link #Throwable(String,Throwable)}, or this method has already
      *         been called on this throwable.
      * @since  1.4
      */
     public synchronized Throwable initCause(Throwable cause) {
         if (this.cause != this)
             throw new IllegalStateException("Can't overwrite cause");
         if (cause == this)
             throw new IllegalArgumentException("Self-causation not permitted");
         this.cause = cause;
         return this;
     }
 
     /**
      * Returns a short description of this throwable.
      * The result is the concatenation of:
      * <ul>
      * <li> the {@linkplain Class#getName() name} of the class of this object
      * <li> ": " (a colon and a space)
      * <li> the result of invoking this object's {@link #getLocalizedMessage}
      *      method
      * </ul>
      * If {@code getLocalizedMessage} returns {@code null}, then just
      * the class name is returned.
      *
      * @return a string representation of this throwable.
      */
     public String toString() {
         String s = getClass().getName();
         String message = getLocalizedMessage();
         return (message != null) ? (s + ": " + message) : s;
     }
 
     /**
      * Prints this throwable and its backtrace to the
      * standard error stream. This method prints a stack trace for this
      * {@code Throwable} object on the error output stream that is
      * the value of the field {@code System.err}. The first line of
      * output contains the result of the {@link #toString()} method for
      * this object.  Remaining lines represent data previously recorded by
      * the method {@link #fillInStackTrace()}. The format of this
      * information depends on the implementation, but the following
      * example may be regarded as typical:
      * <blockquote><pre>
      * java.lang.NullPointerException
      *         at MyClass.mash(MyClass.java:9)
      *         at MyClass.crunch(MyClass.java:6)
      *         at MyClass.main(MyClass.java:3)
      * </pre></blockquote>
      * This example was produced by running the program:
      * <pre>
      * class MyClass {
      *     public static void main(String[] args) {
      *         crunch(null);
      *     }
      *     static void crunch(int[] a) {
      *         mash(a);
      *     }
      *     static void mash(int[] b) {
      *         System.out.println(b[0]);
      *     }
      * }
      * </pre>
      * The backtrace for a throwable with an initialized, non-null cause
      * should generally include the backtrace for the cause.  The format
      * of this information depends on the implementation, but the following
      * example may be regarded as typical:
      * <pre>
      * HighLevelException: MidLevelException: LowLevelException
      *         at Junk.a(Junk.java:13)
      *         at Junk.main(Junk.java:4)
      * Caused by: MidLevelException: LowLevelException
      *         at Junk.c(Junk.java:23)
      *         at Junk.b(Junk.java:17)
      *         at Junk.a(Junk.java:11)
      *         ... 1 more
      * Caused by: LowLevelException
      *         at Junk.e(Junk.java:30)
      *         at Junk.d(Junk.java:27)
      *         at Junk.c(Junk.java:21)
      *         ... 3 more
      * </pre>
      * Note the presence of lines containing the characters {@code "..."}.
      * These lines indicate that the remainder of the stack trace for this
      * exception matches the indicated number of frames from the bottom of the
      * stack trace of the exception that was caused by this exception (the
      * "enclosing" exception).  This shorthand can greatly reduce the length
      * of the output in the common case where a wrapped exception is thrown
      * from same method as the "causative exception" is caught.  The above
      * example was produced by running the program:
      * <pre>
      * public class Junk {
      *     public static void main(String args[]) {
      *         try {
      *             a();
      *         } catch(HighLevelException e) {
      *             e.printStackTrace();
      *         }
      *     }
      *     static void a() throws HighLevelException {
      *         try {
      *             b();
      *         } catch(MidLevelException e) {
      *             throw new HighLevelException(e);
      *         }
      *     }
      *     static void b() throws MidLevelException {
      *         c();
      *     }
      *     static void c() throws MidLevelException {
      *         try {
      *             d();
      *         } catch(LowLevelException e) {
      *             throw new MidLevelException(e);
      *         }
      *     }
      *     static void d() throws LowLevelException {
      *        e();
      *     }
      *     static void e() throws LowLevelException {
      *         throw new LowLevelException();
      *     }
      * }
      *
      * class HighLevelException extends Exception {
      *     HighLevelException(Throwable cause) { super(cause); }
      * }
      *
      * class MidLevelException extends Exception {
      *     MidLevelException(Throwable cause)  { super(cause); }
      * }
      *
      * class LowLevelException extends Exception {
      * }
      * </pre>
      * As of release 7, the platform supports the notion of
      * <i>suppressed exceptions</i> (in conjunction with the {@code
      * try}-with-resources statement). Any exceptions that were
      * suppressed in order to deliver an exception are printed out
      * beneath the stack trace.  The format of this information
      * depends on the implementation, but the following example may be
      * regarded as typical:
      *
      * <pre>
      * Exception in thread "main" java.lang.Exception: Something happened
      *  at Foo.bar(Foo.java:10)
      *  at Foo.main(Foo.java:5)
      *  Suppressed: Resource$CloseFailException: Resource ID = 0
      *          at Resource.close(Resource.java:26)
      *          at Foo.bar(Foo.java:9)
      *          ... 1 more
      * </pre>
      * Note that the "... n more" notation is used on suppressed exceptions
      * just at it is used on causes. Unlike causes, suppressed exceptions are
      * indented beyond their "containing exceptions."
      *
      * <p>An exception can have both a cause and one or more suppressed
      * exceptions:
      * <pre>
      * Exception in thread "main" java.lang.Exception: Main block
      *  at Foo3.main(Foo3.java:7)
      *  Suppressed: Resource$CloseFailException: Resource ID = 2
      *          at Resource.close(Resource.java:26)
      *          at Foo3.main(Foo3.java:5)
      *  Suppressed: Resource$CloseFailException: Resource ID = 1
      *          at Resource.close(Resource.java:26)
      *          at Foo3.main(Foo3.java:5)
      * Caused by: java.lang.Exception: I did it
      *  at Foo3.main(Foo3.java:8)
      * </pre>
      * Likewise, a suppressed exception can have a cause:
      * <pre>
      * Exception in thread "main" java.lang.Exception: Main block
      *  at Foo4.main(Foo4.java:6)
      *  Suppressed: Resource2$CloseFailException: Resource ID = 1
      *          at Resource2.close(Resource2.java:20)
      *          at Foo4.main(Foo4.java:5)
      *  Caused by: java.lang.Exception: Rats, you caught me
      *          at Resource2$CloseFailException.<init>(Resource2.java:45)
      *          ... 2 more
      * </pre>
      */
     public void printStackTrace() {
         printStackTrace(System.err);
     }
 
     /**
      * Prints this throwable and its backtrace to the specified print stream.
      *
      * @param s {@code PrintStream} to use for output
      */
     public void printStackTrace(PrintStream s) {
         printStackTrace(new WrappedPrintStream(s));
     }
 
     private void printStackTrace(PrintStreamOrWriter s) {
         // Guard against malicious overrides of Throwable.equals by
         // using a Set with identity equality semantics.
         Set<Throwable> dejaVu =
             Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
         dejaVu.add(this);
 
         synchronized (s.lock()) {
             // Print our stack trace
             s.println(this);
             StackTraceElement[] trace = getOurStackTrace();
             for (StackTraceElement traceElement : trace)
                 s.println("\tat " + traceElement);
 
             // Print suppressed exceptions, if any
             for (Throwable se : getSuppressed())
                 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
 
             // Print cause, if any
             Throwable ourCause = getCause();
             if (ourCause != null)
                 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
         }
     }
 
     /**
      * Print our stack trace as an enclosed exception for the specified
      * stack trace.
      */
     private void printEnclosedStackTrace(PrintStreamOrWriter s,
                                          StackTraceElement[] enclosingTrace,
                                          String caption,
                                          String prefix,
                                          Set<Throwable> dejaVu) {
         assert Thread.holdsLock(s.lock());
         if (dejaVu.contains(this)) {
             s.println("\t[CIRCULAR REFERENCE:" + this + "]");
         } else {
             dejaVu.add(this);
             // Compute number of frames in common between this and enclosing trace
             StackTraceElement[] trace = getOurStackTrace();
             int m = trace.length - 1;
             int n = enclosingTrace.length - 1;
             while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
                 m--; n--;
             }
             int framesInCommon = trace.length - 1 - m;
 
             // Print our stack trace
             s.println(prefix + caption + this);
             for (int i = 0; i <= m; i++)
                 s.println(prefix + "\tat " + trace[i]);
             if (framesInCommon != 0)
                 s.println(prefix + "\t... " + framesInCommon + " more");
 
             // Print suppressed exceptions, if any
             for (Throwable se : getSuppressed())
                 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
                                            prefix +"\t", dejaVu);
 
             // Print cause, if any
             Throwable ourCause = getCause();
             if (ourCause != null)
                 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
         }
     }
 
     /**
      * Prints this throwable and its backtrace to the specified
      * print writer.
      *
      * @param s {@code PrintWriter} to use for output
      * @since   JDK1.1
      */
     public void printStackTrace(PrintWriter s) {
         printStackTrace(new WrappedPrintWriter(s));
     }
 
     /**
      * Wrapper class for PrintStream and PrintWriter to enable a single
      * implementation of printStackTrace.
      */
     private abstract static class PrintStreamOrWriter {
         /** Returns the object to be locked when using this StreamOrWriter */
         abstract Object lock();
 
         /** Prints the specified string as a line on this StreamOrWriter */
         abstract void println(Object o);
     }
 
     private static class WrappedPrintStream extends PrintStreamOrWriter {
         private final PrintStream printStream;
 
         WrappedPrintStream(PrintStream printStream) {
             this.printStream = printStream;
         }
 
         Object lock() {
             return printStream;
         }
 
         void println(Object o) {
             printStream.println(o);
         }
     }
 
     private static class WrappedPrintWriter extends PrintStreamOrWriter {
         private final PrintWriter printWriter;
 
         WrappedPrintWriter(PrintWriter printWriter) {
             this.printWriter = printWriter;
         }
 
         Object lock() {
             return printWriter;
         }
 
         void println(Object o) {
             printWriter.println(o);
         }
     }
 
     /**
      * Fills in the execution stack trace. This method records within this
      * {@code Throwable} object information about the current state of
      * the stack frames for the current thread.
      *
      * <p>If the stack trace of this {@code Throwable} {@linkplain
      * Throwable#Throwable(String, Throwable, boolean, boolean) is not
      * writable}, calling this method has no effect.
      *
      * @return  a reference to this {@code Throwable} instance.
      * @see     java.lang.Throwable#printStackTrace()
      */
     public synchronized Throwable fillInStackTrace() {
         if (stackTrace != null ||
             backtrace != null /* Out of protocol state */ ) {
             fillInStackTrace(0);
             stackTrace = UNASSIGNED_STACK;
         }
         return this;
     }
 
     private native Throwable fillInStackTrace(int dummy);
 
     /**
      * Provides programmatic access to the stack trace information printed by
      * {@link #printStackTrace()}.  Returns an array of stack trace elements,
      * each representing one stack frame.  The zeroth element of the array
      * (assuming the array's length is non-zero) represents the top of the
      * stack, which is the last method invocation in the sequence.  Typically,
      * this is the point at which this throwable was created and thrown.
      * The last element of the array (assuming the array's length is non-zero)
      * represents the bottom of the stack, which is the first method invocation
      * in the sequence.
      *
      * <p>Some virtual machines may, under some circumstances, omit one
      * or more stack frames from the stack trace.  In the extreme case,
      * a virtual machine that has no stack trace information concerning
      * this throwable is permitted to return a zero-length array from this
      * method.  Generally speaking, the array returned by this method will
      * contain one element for every frame that would be printed by
      * {@code printStackTrace}.  Writes to the returned array do not
      * affect future calls to this method.
      *
      * @return an array of stack trace elements representing the stack trace
      *         pertaining to this throwable.
      * @since  1.4
      */
     public StackTraceElement[] getStackTrace() {
         return getOurStackTrace().clone();
     }
 
     private synchronized StackTraceElement[] getOurStackTrace() {
         // Initialize stack trace field with information from
         // backtrace if this is the first call to this method
         if (stackTrace == UNASSIGNED_STACK ||
             (stackTrace == null && backtrace != null) /* Out of protocol state */) {
             int depth = getStackTraceDepth();
             stackTrace = new StackTraceElement[depth];
             for (int i=0; i < depth; i++)
                 stackTrace[i] = getStackTraceElement(i);
         } else if (stackTrace == null) {
             return UNASSIGNED_STACK;
         }
         return stackTrace;
     }
 
     /**
      * Sets the stack trace elements that will be returned by
      * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
      * and related methods.
      *
      * This method, which is designed for use by RPC frameworks and other
      * advanced systems, allows the client to override the default
      * stack trace that is either generated by {@link #fillInStackTrace()}
      * when a throwable is constructed or deserialized when a throwable is
      * read from a serialization stream.
      *
      * <p>If the stack trace of this {@code Throwable} {@linkplain
      * Throwable#Throwable(String, Throwable, boolean, boolean) is not
      * writable}, calling this method has no effect other than
      * validating its argument.
      *
      * @param   stackTrace the stack trace elements to be associated with
      * this {@code Throwable}.  The specified array is copied by this
      * call; changes in the specified array after the method invocation
      * returns will have no affect on this {@code Throwable}'s stack
      * trace.
      *
      * @throws NullPointerException if {@code stackTrace} is
      *         {@code null} or if any of the elements of
      *         {@code stackTrace} are {@code null}
      *
      * @since  1.4
      */
     public void setStackTrace(StackTraceElement[] stackTrace) {
         // Validate argument
         StackTraceElement[] defensiveCopy = stackTrace.clone();
         for (int i = 0; i < defensiveCopy.length; i++) {
             if (defensiveCopy[i] == null)
                 throw new NullPointerException("stackTrace[" + i + "]");
         }
 
         synchronized (this) {
             if (this.stackTrace == null && // Immutable stack
                 backtrace == null) // Test for out of protocol state
                 return;
             this.stackTrace = defensiveCopy;
         }
     }
 
     /**
      * Returns the number of elements in the stack trace (or 0 if the stack
      * trace is unavailable).
      *
      * package-protection for use by SharedSecrets.
      */
     native int getStackTraceDepth();
 
     /**
      * Returns the specified element of the stack trace.
      *
      * package-protection for use by SharedSecrets.
      *
      * @param index index of the element to return.
      * @throws IndexOutOfBoundsException if {@code index < 0 ||
      *         index >= getStackTraceDepth() }
      */
     native StackTraceElement getStackTraceElement(int index);
 
     /**
      * Reads a {@code Throwable} from a stream, enforcing
      * well-formedness constraints on fields.  Null entries and
      * self-pointers are not allowed in the list of {@code
      * suppressedExceptions}.  Null entries are not allowed for stack
      * trace elements.  A null stack trace in the serial form results
      * in a zero-length stack element array. A single-element stack
      * trace whose entry is equal to {@code new StackTraceElement("",
      * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code
      * stackTrace} field.
      *
      * Note that there are no constraints on the value the {@code
      * cause} field can hold; both {@code null} and {@code this} are
      * valid values for the field.
      */
     private void readObject(ObjectInputStream s)
         throws IOException, ClassNotFoundException {
         s.defaultReadObject();     // read in all fields
         if (suppressedExceptions != null) {
             List<Throwable> suppressed = null;
             if (suppressedExceptions.isEmpty()) {
                 // Use the sentinel for a zero-length list
                 suppressed = SUPPRESSED_SENTINEL;
             } else { // Copy Throwables to new list
                 suppressed = new ArrayList<>(1);
                 for (Throwable t : suppressedExceptions) {
                     // Enforce constraints on suppressed exceptions in
                     // case of corrupt or malicious stream.
                     if (t == null)
                         throw new NullPointerException(NULL_CAUSE_MESSAGE);
                     if (t == this)
                         throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
                     suppressed.add(t);
                 }
             }
             suppressedExceptions = suppressed;
         } // else a null suppressedExceptions field remains null
 
         /*
          * For zero-length stack traces, use a clone of
          * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to
          * allow identity comparison against UNASSIGNED_STACK in
          * getOurStackTrace.  The identity of UNASSIGNED_STACK in
          * stackTrace indicates to the getOurStackTrace method that
          * the stackTrace needs to be constructed from the information
          * in backtrace.
          */
         if (stackTrace != null) {
             if (stackTrace.length == 0) {
                 stackTrace = UNASSIGNED_STACK.clone();
             }  else if (stackTrace.length == 1 &&
                         // Check for the marker of an immutable stack trace
                         SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) {
                 stackTrace = null;
             } else { // Verify stack trace elements are non-null.
                 for(StackTraceElement ste : stackTrace) {
                     if (ste == null)
                         throw new NullPointerException("null StackTraceElement in serial stream. ");
                 }
             }
         } else {
             // A null stackTrace field in the serial form can result
             // from an exception serialized without that field in
             // older JDK releases; treat such exceptions as having
             // empty stack traces.
             stackTrace = UNASSIGNED_STACK.clone();
         }
     }
 
     /**
      * Write a {@code Throwable} object to a stream.
      *
      * A {@code null} stack trace field is represented in the serial
      * form as a one-element array whose element is equal to {@code
      * new StackTraceElement("", "", null, Integer.MIN_VALUE)}.
      */
     private synchronized void writeObject(ObjectOutputStream s)
         throws IOException {
         // Ensure that the stackTrace field is initialized to a
         // non-null value, if appropriate.  As of JDK 7, a null stack
         // trace field is a valid value indicating the stack trace
         // should not be set.
         getOurStackTrace();
 
         StackTraceElement[] oldStackTrace = stackTrace;
         try {
             if (stackTrace == null)
                 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL;
             s.defaultWriteObject();
         } finally {
             stackTrace = oldStackTrace;
         }
     }
 
     /**
      * Appends the specified exception to the exceptions that were
      * suppressed in order to deliver this exception. This method is
      * thread-safe and typically called (automatically and implicitly)
      * by the {@code try}-with-resources statement.
      *
      * <p>The suppression behavior is enabled <em>unless</em> disabled
      * {@linkplain #Throwable(String, Throwable, boolean, boolean) via
      * a constructor}.  When suppression is disabled, this method does
      * nothing other than to validate its argument.
      *
      * <p>Note that when one exception {@linkplain
      * #initCause(Throwable) causes} another exception, the first
      * exception is usually caught and then the second exception is
      * thrown in response.  In other words, there is a causal
      * connection between the two exceptions.
      *
      * In contrast, there are situations where two independent
      * exceptions can be thrown in sibling code blocks, in particular
      * in the {@code try} block of a {@code try}-with-resources
      * statement and the compiler-generated {@code finally} block
      * which closes the resource.
      *
      * In these situations, only one of the thrown exceptions can be
      * propagated.  In the {@code try}-with-resources statement, when
      * there are two such exceptions, the exception originating from
      * the {@code try} block is propagated and the exception from the
      * {@code finally} block is added to the list of exceptions
      * suppressed by the exception from the {@code try} block.  As an
      * exception unwinds the stack, it can accumulate multiple
      * suppressed exceptions.
      *
      * <p>An exception may have suppressed exceptions while also being
      * caused by another exception.  Whether or not an exception has a
      * cause is semantically known at the time of its creation, unlike
      * whether or not an exception will suppress other exceptions
      * which is typically only determined after an exception is
      * thrown.
      *
      * <p>Note that programmer written code is also able to take
      * advantage of calling this method in situations where there are
      * multiple sibling exceptions and only one can be propagated.
      *
      * @param exception the exception to be added to the list of
      *        suppressed exceptions
      * @throws IllegalArgumentException if {@code exception} is this
      *         throwable; a throwable cannot suppress itself.
      * @throws NullPointerException if {@code exception} is {@code null}
      * @since 1.7
      */
     public final synchronized void addSuppressed(Throwable exception) {
         if (exception == this)
             throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
 
         if (exception == null)
             throw new NullPointerException(NULL_CAUSE_MESSAGE);
 
         if (suppressedExceptions == null) // Suppressed exceptions not recorded
             return;
 
         if (suppressedExceptions == SUPPRESSED_SENTINEL)
             suppressedExceptions = new ArrayList<>(1);
 
         suppressedExceptions.add(exception);
     }
 
     private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
 
     /**
      * Returns an array containing all of the exceptions that were
      * suppressed, typically by the {@code try}-with-resources
      * statement, in order to deliver this exception.
      *
      * If no exceptions were suppressed or {@linkplain
      * #Throwable(String, Throwable, boolean, boolean) suppression is
      * disabled}, an empty array is returned.  This method is
      * thread-safe.  Writes to the returned array do not affect future
      * calls to this method.
      *
      * @return an array containing all of the exceptions that were
      *         suppressed to deliver this exception.
      * @since 1.7
      */
     public final synchronized Throwable[] getSuppressed() {
         if (suppressedExceptions == SUPPRESSED_SENTINEL ||
             suppressedExceptions == null)
             return EMPTY_THROWABLE_ARRAY;
         else
             return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
     }
 }