java.lang
Class Throwable

java.lang.Object
  java.lang.Throwable

Direct Known Subclasses:

Error, Exception

public class Throwable
extends Object

The Throwable class is the superclass of all errors and exceptions in the Java language. Only objects that are instances of this class (or of 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, 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).

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 an error message.

A Throwable class 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.

Here is one example of catching an exception:

     try {
         int a[] = new int[2];
         a[4];
     } catch (ArrayIndexOutOfBoundsException e) {
         System.out.println("exception: " + e.getMessage());
         e.printStackTrace();
     }
 

RIM Implementation Note

Only uncaught exceptions have stack traces. The VM checks the current catch stack and if it finds anything that will catch the exception, it eliminates the stack trace to save time and memory. Any code in the current stack such as catch (Exception e) eliminates the stack trace.

If the exception is never caught, then the stack trace is generated.The stack trace is also generated if there is code such as catch (Throwable t).

Since:

JDK1.0

Constructor Summary

Throwable()
Constructs a new Throwable with null as its error message string.

Throwable(String message)
Constructs a new Throwable with the specified error message.

Method Summary
String	getMessage() Returns the error message string of this throwable object.
void	printStackTrace() Prints this Throwable and its backtrace to the standard error stream.
String	toString() Returns a short description of this throwable object.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Throwable

public Throwable()

Constructs a new Throwable with null as its error message string. Also, the method

Throwable

public Throwable(String message)

Constructs a new Throwable with the specified error message.

Parameters:

message - the error message. The error message is saved for later retrieval by the Throwable.getMessage() method.

Method Detail

getMessage

public String getMessage()

Returns the error message string of this throwable object.

Returns:

the error message string of this Throwable object if it was created with an error message string; or null if it was created with no error message.

toString

public String toString()

Returns a short description of this throwable object. If this Throwable object was created with an error 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 Throwable.getMessage() method for this object

If this Throwable object was created with no error message string, then the name of the actual class of this object 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.