Java Reference
In-Depth Information
When you create your own classes or write programs, exceptions are likely to occur. As
you have seen, Java provides a substantial number of exception classes to deal with these
situations. However, it does not provide all the exception classes you will ever need.
Therefore, Java enables programmers to create exception classes to handle the exceptions
not covered by Java's exception classes or to handle their own exceptions. This section
describes how to create your own exception classes.
Java's mechanism to process the exceptions you define is the same as that for built-in
exceptions. However, you must
throw your own exceptions using the
throw
statement.
The exception class that you define extends either the
class
Exception
or one of
its subclasses. Also, a subclass of the
class
Exception
is either a predefined class or
a user-defined class. In other words, if you have created an exception class, you can
define other exception classes by extending the definition of the exception class you
created.
Typically, constructors are the only methods that you include when you define your own
exception class. Because the exception class you define is a subclass of an existing
exception class, either built-in or user-defined, the exception class that you define inherits
the members of the superclass. Therefore, objects of the exception classes can use the
public
members of the superclasses.
Because the
class
Exception
is derived from the
class
Throwable
, it inherits the
methods
getMessage
and
toString
of the
class
Throwable
. These methods are
public
, so they are also inherited by the subclasses of the
class
Exception
.
EXAMPLE 11-12
This example shows how to create your own division by the zero exception class.
public class
MyDivisionByZeroException
extends
Exception
{
public
MyDivisionByZeroException()
{
super
("Cannot divide by zero");
}
public
MyDivisionByZeroException(String strMessage)
{
super
(strMessage);
}
}
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