Java Reference
In-Depth Information
your program should handle exceptions of these types. An important subclass of
Excep-
tion
is
RuntimeException
, which is used to represent various common types of run-time
errors.
Exception Handling Fundamentals
Java exception handling is managed via five keywords:
try
,
catch
,
throw
,
throws
, and
fi-
nally
. They form an interrelated subsystem in which the use of one implies the use of an-
other. Throughout the course of this chapter, each keyword is examined in detail. However,
it is useful at the outset to have a general understanding of the role each plays in exception
handling. Briefly, here is how they work.
Program statements that you want to monitor for exceptions are contained within a
try
block. If an exception occurs within the
try
block, it is
thrown
. Your code can catch this
exception using
catch
and handle it in some rational manner. System-generated exceptions
are automatically thrown by the Java run-time system. To manually throw an exception,
use the keyword
throw
. In some cases, an exception that is thrown out of a method must
be specified as such by a
throws
clause. Any code that absolutely must be executed upon
exiting from a
try
block is put in a
finally
block.
Ask the Expert
Q
:
Just to be sure, could you review the conditions that cause an exception to be
generated?
A
:
Exceptions are generated in three different ways. First, the Java Virtual Machine can
generate an exception in response to some internal error which is beyond your con-
trol. Normally, your program won't handle these types of exceptions. Second, stand-
ard exceptions, such as those corresponding to divide-by-zero or array index out-of-
bounds, are generated by errors in program code. You need to handle these excep-
tions. Third, you can manually generate an exception by using the
throw
statement.
No matter how an exception is generated, it is handled in the same way.
Using try and catch
