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). + * + *
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 cause: another throwable that caused this + * throwable to be constructed. The recording of this causal information + * is referred to as the chained exception facility, as the + * cause can, itself, have a cause, and so on, leading to a "chain" of + * exceptions, each caused by another. + * + *
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). + * + *
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.) + * + *
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}. + * + *
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: 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}.
+ *
+ * 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. Note that the detail message associated with
+ * {@code cause} is not automatically incorporated in
+ * this throwable's detail message.
+ *
+ * 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}).
+ *
+ * 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.
+ *
+ * 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.)
+ *
+ * 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 not
+ * 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 cause of this throwable to the specified value.
+ * (The cause is the throwable that caused this throwable to get thrown.)
+ *
+ * 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.
+ *
+ * An example of using this method on a legacy throwable type
+ * without other support for setting the cause is:
+ *
+ * An exception can have both a cause and one or more suppressed
+ * exceptions:
+ * 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.
+ *
+ * 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.
+ *
+ * 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 The suppression behavior is enabled unless disabled
+ * {@linkplain #Throwable(String, Throwable, boolean, boolean) via
+ * a constructor}. When suppression is disabled, this method does
+ * nothing other than to validate its argument.
+ *
+ * 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.
+ *
+ * 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.
+ *
+ * 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);
+ }
+}
+ * {@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
+ * try {
+ * lowLevelOp();
+ * } catch (LowLevelException le) {
+ * throw (HighLevelException)
+ * new HighLevelException().initCause(le); // Legacy constructor
+ * }
+ *
+ *
+ * @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:
+ *
+ *
+ * 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:
+ *
+ * This example was produced by running the program:
+ *
+ * java.lang.NullPointerException
+ * at MyClass.mash(MyClass.java:9)
+ * at MyClass.crunch(MyClass.java:6)
+ * at MyClass.main(MyClass.java:3)
+ *
+ * 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]);
+ * }
+ * }
+ *
+ * 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:
+ *
+ * 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
+ *
+ * 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:
+ *
+ * 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 {
+ * }
+ *
+ * As of release 7, the platform supports the notion of
+ * suppressed exceptions (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:
+ *
+ *
+ * Exception in thread "main" java.lang.Exception: Something happened
+ * at Foo.bar(Foo.java:10)
+ * at Foo.main(Foo.java:5)
+ * Suppressed: Resource$CloseFailException: Resource ID = 0
+ * at Resource.close(Resource.java:26)
+ * at Foo.bar(Foo.java:9)
+ * ... 1 more
+ *
+ * Note that the "... n more" notation is used on suppressed exceptions
+ * just at it is used on causes. Unlike causes, suppressed exceptions are
+ * indented beyond their "containing exceptions."
+ *
+ *
+ * Exception in thread "main" java.lang.Exception: Main block
+ * at Foo3.main(Foo3.java:7)
+ * Suppressed: Resource$CloseFailException: Resource ID = 2
+ * at Resource.close(Resource.java:26)
+ * at Foo3.main(Foo3.java:5)
+ * Suppressed: Resource$CloseFailException: Resource ID = 1
+ * at Resource.close(Resource.java:26)
+ * at Foo3.main(Foo3.java:5)
+ * Caused by: java.lang.Exception: I did it
+ * at Foo3.main(Foo3.java:8)
+ *
+ * Likewise, a suppressed exception can have a cause:
+ *
+ * Exception in thread "main" java.lang.Exception: Main block
+ * at Foo4.main(Foo4.java:6)
+ * Suppressed: Resource2$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.
+ */
+ 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