/*

  * 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

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  */

 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);

     }

 }