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## java.lang
Class Throwable

    java.lang.Object
      |
      +--java.lang.Throwable

All Implemented Interfaces:
  Serializable

Direct Known Subclasses:
  Error, Exception

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 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();
>          }

Since:
  JDK1.0
See Also:
  Serialized Form

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
`Throwable` | `fillInStackTrace()` Fills in the execution stack trace.
`String` | `getLocalizedMessage()` Creates a localized description of this `Throwable`.
`String` | `getMessage()` Returns the error message string of this throwable object.
`void` | `printStackTrace()` Prints this `Throwable` and its backtrace to the standard error stream.
`void` | `printStackTrace(PrintStream s)` Prints this `Throwable` and its backtrace to the specified print stream.
`void` | `printStackTrace(PrintWriter s)` Prints this `Throwable` and its backtrace to the specified print writer.
`String` | `toString()` Returns a short description of this throwable object.

Methods inherited from class java.lang.Object
`clone, equals, finalize, 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 `fillInStackTrace()` is called for this object.

### Throwable

    public Throwable(String message)

  Constructs a new `Throwable` with the specified error message. Also, the method `fillInStackTrace()` is called for this object.
  Parameters:
    `message` - the error message. The error message is saved for later retrieval by the `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.

### 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:
    JDK1.1

### 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 `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. 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[] argv) {
  >              crunch(null);
  >          }
  >          static void crunch(int[] a) {
  >              mash(a);
  >          }

  >          static void mash(int[] b) {
  >              System.out.println(b[0]);
  >          }
  >      }

  See Also:
    `System.err`

### 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:
    JDK1.1

### 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. This method is useful when an application is re-throwing an error or exception. For example:

  >          try {
  >              a = b / c;
  >          } catch(ArithmeticThrowable e) {
  >              a = Double.MAX_VALUE;
  >              throw e.fillInStackTrace();
  >          }

  Returns:
    this `Throwable` object.
  See Also:
    `printStackTrace()`

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