Java Reference
In-Depth Information
C
HAPTER
S
UMMARY
1.
Exception handling enables a method to throw an exception to its caller.
2.
A Java
exception
is an instance of a class derived from
java.lang.Throwable
.
Java provides a number of predefined exception classes, such as
Error
,
Exception
,
RuntimeException
,
ClassNotFoundException
,
NullPointerException
,
and
ArithmeticException
. You can also define your own exception class by
extending
Exception
.
3.
Exceptions occur during the execution of a method.
RuntimeException
and
Error
are
unchecked exceptions
; all other exceptions are
checked
.
4.
When
declaring a method
, you have to declare a checked exception if the method
might throw it, thus telling the compiler what can go wrong.
5.
The keyword for declaring an exception is
throws
, and the keyword for throwing an
exception is
throw
.
6.
To invoke the method that declares checked exceptions, enclose it in a
try
statement.
When an exception occurs during the execution of the method, the
catch
block
catches and handles the exception.
7.
If an exception is not caught in the current method, it is passed to its caller. The
process is repeated until the exception is caught or passed to the
main
method.
8.
Various exception classes can be derived from a common superclass. If a
catch
block catches the exception objects of a superclass, it can also catch all the exception
objects of the subclasses of that superclass.
9.
The order in which exceptions are specified in a
catch
block is important. A compile
error will result if you specify an exception object of a class after an exception object
of the superclass of that class.
10.
When an exception occurs in a method, the method exits immediately if it does not
catch the exception. If the method is required to perform some task before exiting,
you can catch the exception in the method and then rethrow it to its caller.
11.
The code in the
finally
block is executed under all circumstances, regardless of
whether an exception occurs in the
try
block or whether an exception is caught if
it occurs.
12.
Exception handling separates error-handling code from normal programming tasks,
thus making programs easier to read and to modify.
13.
Exception handling should not be used to replace simple tests. You should perform
simple test using
if
statements whenever possible, and reserve exception handling
for dealing with situations that cannot be handled with
if
statements.
14.
The
File
class is used to obtain file properties and manipulate files. It does not con-
tain the methods for creating a file or for reading/writing data from/to a file.
