Exception Objects

Here is a try/catch structure:

try
{
  // statements, some of which might throw an exception
}

catch ( SomeExceptionType ex )
{
  // statements to handle this type of exception
}

....  // perhaps more catch blocks

....  // perhaps a finally block

When a catch{} block receives control (ie. starts execution) it has a reference to an object of class Exception (or a subclass of Exception). The specific class of the object depends on what exception was thrown. An exception will be caught if its class or an ancestor class is in the list of catch{} blocks.

When an exception event occurs while a program is running, the Java run time system takes over, creates an Exception object to represent the event. Information about the event is put in the object. If the exception arose inside a try{} block, the Java run time system sends the Exceptioncatch{} block (if there is one).

Exception objects are actual Java objects. They have member data and member methods, including:

• public void printStackTrace()
  • Print a stack trace ― a list that shows the sequence of method calls up to this exception.
• public String getMessage()
  • Return a string that may describe what went wrong.

A catch{} block can use these methods to write an informative error message to the monitor.

int[] value = new int[10];