Throwable (Java SE 9 JDK 9 )()

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public class Throwable

 

  extends Object

  implements Serializable

 

  The 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 throw statement. Similarly, only

   this class or one of its subclasses can be the argument type in a

   catch clause.

   For the purposes of compile-time checking of exceptions,

   Throwable and any subclass of Throwable that is not also a

   subclass of either RuntimeException or Error are

   regarded as checked exceptions.

   Instances of two subclasses, Error and

   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 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 layers 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 Collection interface, and that its persistence is implemented atop

   java.io. Suppose the internals of the add method

   can throw an IOException. The implementation

   can communicate the details of the IOException to its caller

   while conforming to the Collection interface by wrapping the

   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

   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

   Throwable constructors that takes a cause.

   Because the 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

   Throwable.

   By convention, class Throwable and its subclasses have two

   constructors, one that takes no arguments and one that takes a

   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

   Throwable (the cause), and one that takes a

   String (the detail message) and a Throwable (the

   cause).

  Since:

  See Also:

  Serialized Form

  See The Java Language Specification:

  11.2 Compile-Time Checking of Exceptions

  
 

  Throwable (Stringmessage)

  Constructs a new throwable with the specified detail message.

  
protected

  Throwable (Stringmessage,

   Throwablecause,

   booleanenableSuppression,

   booleanwritableStackTrace)

  Constructs a new throwable with the specified detail message,

   cause, suppression enabled or

   disabled, and writable stack trace enabled or disabled.

  
 

  Throwable (Throwablecause)

  Constructs a new throwable with the specified cause and a detail

   message of (cause==null ? null : cause.toString()) (which

   typically contains the class and detail message of cause).

  
addSuppressed (Throwableexception)

  Appends the specified exception to the exceptions that were

   suppressed in order to deliver this exception.

  
Throwable[]

  getSuppressed ()

  Returns an array containing all of the exceptions that were

   suppressed, typically by the try-with-resources

   statement, in order to deliver this exception.

  


publicThrowable ()

 

  Constructs a new throwable with null as its detail message.

   The cause is not initialized, and may subsequently be initialized by a

   call to initCause(java.lang.Throwable).

   The fillInStackTrace() method is called to initialize

   the stack trace data in the newly created throwable.

  
Throwable

  

publicThrowable (Stringmessage)

 

  Constructs a new throwable with the specified detail message. The

   cause is not initialized, and may subsequently be initialized by

   a call to initCause(java.lang.Throwable).

   The fillInStackTrace() method is called to initialize

   the stack trace data in the newly created throwable.

  Parameters:

  message - the detail message. The detail message is saved for

   later retrieval by the getMessage() method.

  
Throwable

  

publicThrowable (Stringmessage,

 

   Throwablecause)

 

  Constructs a new throwable with the specified detail message and

   cause. Note that the detail message associated with

   cause is not automatically incorporated in

   this throwables detail message.

   The fillInStackTrace() method is called to initialize

   the stack trace data in the newly created throwable.

  Parameters:

  message - the detail message (which is saved for later retrieval

   by the getMessage() method).

  cause - the cause (which is saved for later retrieval by the

   getCause() method). (A null value is

   permitted, and indicates that the cause is nonexistent or

   unknown.)

  Since:

  
Throwable

  

publicThrowable (Throwablecause)

 

  Constructs a new throwable with the specified cause and a detail

   message of (cause==null ? null : cause.toString()) (which

   typically contains the class and detail message of cause).

   This constructor is useful for throwables that are little more than

   wrappers for other throwables (for example, PrivilegedActionException).

   The fillInStackTrace() method is called to initialize

   the stack trace data in the newly created throwable.

  Parameters:

  cause - the cause (which is saved for later retrieval by the

   getCause() method). (A null value is

   permitted, and indicates that the cause is nonexistent or

   unknown.)

  Since:

  
Throwable

  

protectedThrowable (Stringmessage,

 

   Throwablecause,

   booleanenableSuppression,

   booleanwritableStackTrace)

 

  Constructs a new throwable with the specified detail message,

   cause, suppression enabled or

   disabled, and writable stack trace enabled or disabled. If

   suppression is disabled, getSuppressed() for this object

   will return a zero-length array and calls to addSuppressed(java.lang.Throwable) 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 fillInStackTrace(), a null will be written to the

   stackTrace field, and subsequent calls to

   fillInStackTrace and setStackTrace(StackTraceElement[]) will not set the stack

   trace. If the writable stack trace is false, getStackTrace() will return a zero length array.

   Note that the other constructors of Throwable treat

   suppression as being enabled and the stack trace as being

   writable. Subclasses of 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.

  Parameters:

  message - the detail message.

  cause - the cause. (A null value is permitted,

   and indicates that the cause is nonexistent or unknown.)

  enableSuppression - whether or not suppression is enabled or disabled

  writableStackTrace - whether or not the stack trace should be

   writable

  Since:

  See Also:

  OutOfMemoryError,

  NullPointerException,

  ArithmeticException

  
getMessage

  

publicStringgetMessage ()

 

  Returns the detail message string of this throwable.

  Returns:

  the detail message string of this Throwable instance

   (which may be null).

  
getLocalizedMessage

  

publicStringgetLocalizedMessage ()

 

  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

   getMessage().

  Returns:

  The localized description of this throwable.

  Since:

  
getCause

  

publicThrowablegetCause ()

 

  Returns the cause of this throwable or 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 Throwable, or that was set after

   creation with the 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 Throwable. Note that it is not

   necessary to override any of the PrintStackTrace methods,

   all of which invoke the getCause method to determine the

   cause of a throwable.

  Returns:

  the cause of this throwable or null if the

   cause is nonexistent or unknown.

  Since:

  
initCause

  

publicThrowableinitCause (Throwablecause)

 

  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 Throwable(Throwable) or

   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:

  

 

 

   try {

   lowLevelOp();

   } catch (LowLevelException le) {

   throw (HighLevelException)

   new HighLevelException().initCause(le); // Legacy constructor

  

 

  Parameters:

  cause - the cause (which is saved for later retrieval by the

   getCause() method). (A null value is

   permitted, and indicates that the cause is nonexistent or

   unknown.)

  Returns:

  a reference to this Throwable instance.

  Throws:

  IllegalArgumentException - if cause is this

   throwable. (A throwable cannot be its own cause.)

  IllegalStateException - if this throwable was

   created with Throwable(Throwable) or

   Throwable(String,Throwable), or this method has already

   been called on this throwable.

  Since:

  
toString

  

publicStringtoString ()

 

  Returns a short description of this throwable.

   The result is the concatenation of:

   the name of the class of this object

   ": " (a colon and a space)

   the result of invoking this objects getLocalizedMessage()

   method

   If getLocalizedMessage returns null, then just

   the class name is returned.

  Overrides:

  toStringin classObject

  Returns:

  a string representation of this throwable.

  


publicvoidprintStackTrace ()

 

  Prints this throwable and its backtrace to the

   standard error stream. This method prints a stack trace for this

   Throwable object on the error output stream that is

   the value of the field System.err. The first line of

   output contains the result of the toString() method for

   this object. Remaining lines represent data previously recorded by

   the method fillInStackTrace(). The format of this

   information depends on the implementation, but the following

   example may be regarded as typical:

  

 

 

   java.lang.NullPointerException

   at MyClass.mash(MyClass.java:9)

   at MyClass.crunch(MyClass.java:6)

   at MyClass.main(MyClass.java:3)

  

 

   This example was produced by running the program:

  

 

 

   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 "...".

   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

   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."

   An exception can have both a cause and one or more suppressed

   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. init (Resource2.java:45)

   ... 2 more

  

 

  
printStackTrace

  

publicvoidprintStackTrace (PrintStreams)

 

  Prints this throwable and its backtrace to the specified print stream.

  Parameters:

  s - PrintStream to use for output

  
printStackTrace

  

publicvoidprintStackTrace (PrintWriters)

 

  Prints this throwable and its backtrace to the specified

   print writer.

  Parameters:

  s - PrintWriter to use for output

  Since:

  
fillInStackTrace

  

publicThrowablefillInStackTrace ()

 

  Fills in the execution stack trace. This method records within this

   Throwable object information about the current state of

   the stack frames for the current thread.

   If the stack trace of this Throwable is not writable, calling this method has no effect.

  Returns:

  a reference to this Throwable instance.

  See Also:

  printStackTrace()

  
getStackTrace

  

publicStackTraceElement[]getStackTrace ()

 

  Provides programmatic access to the stack trace information printed by

   printStackTrace(). Returns an array of stack trace elements,

   each representing one stack frame. The zeroth element of the array

   (assuming the arrays 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 arrays 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

   printStackTrace. Writes to the returned array do not

   affect future calls to this method.

  Returns:

  an array of stack trace elements representing the stack trace

   pertaining to this throwable.

  Since:

  
setStackTrace

  

publicvoidsetStackTrace (StackTraceElement[]stackTrace)

 

  Sets the stack trace elements that will be returned by

   getStackTrace() and printed by 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 fillInStackTrace()

   when a throwable is constructed or deserialized when a throwable is

   read from a serialization stream.

   If the stack trace of this Throwable is not writable, calling this method has no effect other than

   validating its argument.

  Parameters:

  stackTrace - the stack trace elements to be associated with

   this 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 Throwables stack

   trace.

  Throws:

  NullPointerException - if stackTrace is

   null or if any of the elements of

   stackTrace are null

  Since:

  
addSuppressed

  

public finalvoidaddSuppressed (Throwableexception)

 

  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 try-with-resources statement.

   The suppression behavior is enabled unless disabled

   via a constructor. When suppression is disabled, this method does

   nothing other than to validate its argument.

   Note that when one exception 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 try block of a try-with-resources

   statement and the compiler-generated finally block

   which closes the resource.

   In these situations, only one of the thrown exceptions can be

   propagated. In the try-with-resources statement, when

   there are two such exceptions, the exception originating from

   the try block is propagated and the exception from the

   finally block is added to the list of exceptions

   suppressed by the exception from the 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.

  Parameters:

  exception - the exception to be added to the list of

   suppressed exceptions

  Throws:

  IllegalArgumentException - if exception is this

   throwable; a throwable cannot suppress itself.

  NullPointerException - if exception is null

  Since:

  
getSuppressed

  

public finalThrowable[]getSuppressed ()

 

  Returns an array containing all of the exceptions that were

   suppressed, typically by the try-with-resources

   statement, in order to deliver this exception.

   If no exceptions were suppressed or 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.

  Returns:

  an array containing all of the exceptions that were

   suppressed to deliver this exception.

  Since:

  
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