Java Reference
In-Depth Information
11.1
Introduction
11.2
Example: Divide by Zero without
Exception Handling
11.3
Example: Handling
ArithmeticException
s and
InputMismatchException
s
11.4
When to Use Exception Handling
11.5
Java Exception Hierarchy
11.6
finally
Block
11.7
Stack Unwinding and Obtaining
Information from an Exception Object
11.8
Chained Exceptions
11.9
Declaring New Exception Types
11.10
Preconditions and Postconditions
11.11
Assertions
11.12
try
-with-Resources: Automatic
Resource Deallocation
11.13
Wrap-Up
Summary | Self-Review Exercises | Answers to Self-Review Exercises | Exercises
As you know from Chapter 7, an exception is an indication of a problem that occurs during
a program's execution. Exception handling enables you to create applications that can re-
solve (or handle) exceptions. In many cases, handling an exception allows a program to
continute executing as if no problem had been encountered. The features presented in this
chapter help you write
robust
and
fault-tolerant
programs that can deal with problems and
continue executing or
terminate gracefully
. Java exception handling is based in part on the
work of Andrew Koenig and Bjarne Stroustrup.
1
First, we demonstrate basic exception-handling techniques by handling an exception
that occurs when a method attempts to divide an integer by zero. Next, we introduce sev-
eral classes at the top of Java's exception-handling class hierarchy. As you'll see, only classes
that extend
Throwable
(package
java.lang
) directly or indirectly can be used with excep-
tion handling. We then show how to use
chained exceptions
—when you invoke a method
that indicates an exception, you can throw another exception and chain the original one
to the new one. This enables you to add application-specific information to the orginal
exception. Next, we introduce
preconditions
and
postconditions
, which must be true when
your methods are called and when they return, respectively. We then present
assertions
,
which you can use at development time to help debug your code. We also discuss two
exception-handling features that were introduced in Java SE 7—catching multiple excep-
tions with one catch handler and the new
try
-with-resources statement that automatically
releases a resource after it's used in the
try
block.
This chapter focuses on the exception-handling concepts and presents several
mechanical examples that demonstrate various features. As you'll see in later chapters,
many Java APIs methods throw exceptions that we handle in our code. Figure 11.1 shows
some of the exception types you've already seen and others you'll learn about.
1.
A. Koenig and B. Stroustrup, “Exception Handling for C++ (revised),”
Proceedings of the Usenix C++
Conference
, pp. 149-176, San Francisco, April 1990.
