Exception Handling - Java - page 486

Exception Object Characteristics
The two most important things about an exception object are its type (the exception class)
and a message that it carries in an instance variable of type String . This string can be recov-
ered with the accessor method getMessage . This string allows your code to send a message
along with an exception object, so that the catch block can use the message.

Programmer-Defined Exception Classes
You may define your own exception classes, but every such class must be a derived class of
an already existing exception class (either from one of the standard Java libraries or program-
mer defined).

GUIDELINES
• If you have no compelling reason to use any other class as the base class, use the
class Exception as the base class.
• You should define two (or more) constructors, as described later in this list.
• Your exception class inherits the method getMessage . Normally, you do not need to
add any other methods, but it is legal to do so.
• You should start each constructor definition with a call to the constructor of the base
class, such as the following:

super ("Sample Exception thrown!");

• You should include a no-argument constructor, in which case the call to super should
have a string argument that indicates what kind of exception it is. This string can then
be recovered by using the getMessage method.
• You should also include a constructor that takes a single string argument. In this
case, the string should be an argument in a call to super . That way, the string can be
recovered with a call to getMessage .
EXAMPLE
public class SampleException extends Exception
{
public SampleException()
{
super ("Sample Exception thrown!");
}

public SampleException(String message)
{
super (message);
}
}

extra code
on CD

The class SampleException is on the CD that comes with this text.