java::lang::Throwable Class Reference

The Throwable class is the superclass of all errors and exceptions in the Java language. More...

#include <java_lang_Throwable.h>

Inheritance diagram for java::lang::Throwable:

[legend]Collaboration diagram for java::lang::Throwable:

[legend]List of all members.

Public Types
enum	{   xmogDefaultFlags = xmog_base::GLOBAL, xmogMajorVersion = 3, xmogMinorVersion = 2, xmogPatchVersion = 9,   xmogBuildNumber = 2047 }
typedef ::xmog_java_array_template< ::java::lang::Throwable >	array1D
typedef ::xmog_java_array_template< ::xmog_java_array_template< ::java::lang::Throwable > >	array2D
Public Member Functions
virtual ::java::lang::Throwable	fillInStackTrace (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Fills in the execution stack trace.
virtual ::java::lang::Throwable	getCause (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns the cause of this throwable or null if the cause is nonexistent or unknown.
virtual ::java::lang::String	getLocalizedMessage (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Creates a localized description of this throwable.
virtual ::java::lang::String	getMessage (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns the detail message string of this throwable.
virtual ::java::lang::Throwable	initCause (const ::java::lang::Throwable &cause,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Initializes the cause of this throwable to the specified value.
virtual void	printStackTrace (const ::java::io::PrintWriter &s,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Prints this throwable and its backtrace to the specified print writer.
virtual void	printStackTrace (const ::java::io::PrintStream &s,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Prints this throwable and its backtrace to the specified print stream.
virtual void	printStackTrace (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Prints this throwable and its backtrace to the standard error stream.
	Throwable (const ::java::lang::Throwable &cause,::xmog_dummy _use_java_ctor,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	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).
	Throwable (const ::java::lang::String &message, const ::java::lang::Throwable &cause,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Constructs a new throwable with the specified detail message and cause.
	Throwable (::xmog_dummy _use_java_ctor,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Constructs a new throwable with null as its detail message.
	Throwable (const ::java::lang::String &message,::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Constructs a new throwable with the specified detail message.
virtual ::java::lang::String	toString (::xmog_localenv *p_xenv=NULL, xmog_flags f_xflags=xmogDefaultFlags)
	Returns a short description of this throwable.

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Detailed Description

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.

Instances of two subclasses, and , 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. Finally, it can contain a cause: another throwable that caused this throwable to get thrown. The cause facility is new in release 1.4. It is also known 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 Collection interface, and that its persistence is implemented atop java.io. Suppose the internals of the put 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 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. For example:

                 try {
                     lowLevelOp();
                 } catch (LowLevelException le) {
                     throw new HighLevelException(le);  // Chaining-aware constructor
                 }

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. For example:

                 try {
                     lowLevelOp();
                 } catch (LowLevelException le) {
                     throw (HighLevelException)
                             new HighLevelException().initCause(le);  // Legacy constructor
                 }

Prior to release 1.4, there were many throwables that had their own non-standard exception chaining mechanisms ( , , , , , , and ). As of release 1.4, all of these throwables have been retrofitted to use the standard exception chaining mechanism, while continuing to implement their "legacy" chaining mechanisms for compatibility.

Further, as of release 1.4, many general purpose Throwable classes (for example , , ) have been retrofitted with constructors that take a cause. This was not strictly necessary, due to the existence of the initCause method, but it is more convenient and expressive to delegate to a constructor that takes a cause.

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).

Also introduced in release 1.4 is the method, which allows programmatic access to the stack trace information that was previously available only in text form, via the various forms of the method. This information has been added to the serialized representation of this class so getStackTrace and printStackTrace will operate properly on a throwable that was obtained by deserialization.

Author:

unascribed

Josh Bloch (Added exception chaining and programmatic access to stack trace in 1.4.)

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Constructor & Destructor Documentation

java::lang::Throwable::Throwable (  const ::java::lang::String &  message, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Constructs a new throwable with the specified detail message. The cause is not initialized, and may subsequently be initialized by a call to . The 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 method. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL.

java::lang::Throwable::Throwable (  ::xmog_dummy  _use_java_ctor, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Constructs a new throwable with null as its detail message. The cause is not initialized, and may subsequently be initialized by a call to . The method is called to initialize the stack trace data in the newly created throwable. Parameters: _use_java_ctor  indicates that you want to delegate to a Java constructor whose natural proxy conflicts with a C++ requirement. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL.

java::lang::Throwable::Throwable (  const ::java::lang::String &  message, const ::java::lang::Throwable &  cause, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

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 throwable's detail message. The 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 method). cause  the cause (which is saved for later retrieval by the method). (A null value is permitted, and indicates that the cause is nonexistent or unknown.) p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL.

java::lang::Throwable::Throwable (  const ::java::lang::Throwable &  cause, ::xmog_dummy  _use_java_ctor, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

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, ). The method is called to initialize the stack trace data in the newly created throwable. Parameters: cause  a reference to an outer class instance. _use_java_ctor  indicates that you want to delegate to a Java constructor whose natural proxy conflicts with a C++ requirement. p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL.

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Member Function Documentation

virtual ::java::lang::Throwable java::lang::Throwable::fillInStackTrace (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

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. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: a reference to this Throwable instance.

virtual ::java::lang::Throwable java::lang::Throwable::getCause (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

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 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. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: the cause of this throwable or null if the cause is nonexistent or unknown. Reimplemented in java::lang::reflect::InvocationTargetException, and javax::naming::NamingException.

virtual ::java::lang::String java::lang::Throwable::getLocalizedMessage (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

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(). Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: The localized description of this throwable.

virtual ::java::lang::String java::lang::Throwable::getMessage (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Returns the detail message string of this throwable. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: the detail message string of this Throwable instance (which may be null).

virtual ::java::lang::Throwable java::lang::Throwable::initCause (  const ::java::lang::Throwable &  cause, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

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 or , this method cannot be called even once. Parameters: cause  the cause (which is saved for later retrieval by the method). (A null value is permitted, and indicates that the cause is nonexistent or unknown.) p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: a reference to this Throwable instance. Reimplemented in javax::naming::NamingException.

virtual void java::lang::Throwable::printStackTrace (  const ::java::io::PrintWriter &  s, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

Prints this throwable and its backtrace to the specified print writer. Parameters: s  PrintWriter to use for output p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns:

virtual void java::lang::Throwable::printStackTrace (  const ::java::io::PrintStream &  s, ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

Prints this throwable and its backtrace to the specified print stream. Parameters: s  PrintStream to use for output p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns:

virtual void java::lang::Throwable::printStackTrace (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )  [virtual]

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 method for this object. Remaining lines represent data previously recorded by the method . The format of this information depends on the implementation, but the following example may be regarded as typical: <blockquote> java.lang.NullPointerException at MyClass.mash(MyClass.java:9) at MyClass.crunch(MyClass.java:6) at MyClass.main(MyClass.java:3) </blockquote> 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 { } Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns:

virtual ::java::lang::String java::lang::Throwable::toString (  ::xmog_localenv *  p_xenv = NULL, xmog_flags  f_xflags = xmogDefaultFlags )

Returns a short description of this throwable. If this Throwable object was created with a non-null detail message string, then the result is the concatenation of three strings: The name of the actual class of this object ": " (a colon and a space) The result of the method for this object If this Throwable object was created with a null detail message string, then the name of the actual class of this object is returned. Parameters: p_xenv  the local call environment. The default value is NULL. f_xflags  the flags that allow control over the reference type and other internal matters. The default value is xmog_base::GLOBAL. Returns: a string representation of this throwable. Reimplemented from java::lang::Object. Reimplemented in javax::naming::NamingException.

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The documentation for this class was generated from the following file:

• java_lang_Throwable.h

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