Class Throwable

Method Details

• getMessage

  public String getMessage()

  Returns the detail message string of this throwable.

  Returns:

  the detail message string of this Throwable instance (which may be null).

• getLocalizedMessage

  public String getLocalizedMessage()

  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:

  1.1

• getCause

  public Throwable getCause()

  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:

  1.4

• initCause

  public Throwable initCause(Throwable 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 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:

  1.4

• toString

  public String toString()

  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 object's getLocalizedMessage() method

  If getLocalizedMessage returns null, then just the class name is returned.

  Overrides:

  toString in class Object

  Returns:

  a string representation of this throwable.

• printStackTrace

  public void printStackTrace()

  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 as 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

  public void printStackTrace(PrintStream s)

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

  Parameters:

  s - PrintStream to use for output

• printStackTrace

  public void printStackTrace(PrintWriter s)

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

  Parameters:

  s - PrintWriter to use for output

  Since:

  1.1

• fillInStackTrace

  public Throwable fillInStackTrace()

  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

  public StackTraceElement[] 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 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 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:

  1.4

• setStackTrace

  public void setStackTrace(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 Throwable's stack trace.

  Throws:

  NullPointerException - if stackTrace is null or if any of the elements of stackTrace are null

  Since:

  1.4

• addSuppressed

  public final void addSuppressed(Throwable exception)

  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:

  1.7

• getSuppressed

  public final 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. 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:

  1.7