Exception Handling: A Deeper Look - Java: How to Program Early Objects - page 467

performance and are unnecessary for the program's user. To do so, use the java com-
mand's -ea command-line option, as in
java -ea AssertTest
Software Engineering Observation 11.13
Users shouldn't encounter AssertionError s—these should be used only during program
development. For this reason, you shouldn't catch AssertionError s. Instread, allow the
program to terminate, so you can see the error message, then locate and fix the source of the
problem. You should not use assert to indicate runtime problems in production code (as we
did in Fig. 11.8 for demonstration purposes)—use the exception mechanism for this purpose.
11.12 try -with-Resources: Automatic Resource
Deallocation
Typically resource-release code should be placed in a finally block to ensure that a resource
is released, regardless of whether there were exceptions when the resource was used in the
corresponding try block. An alternative notation—the try -with-resources statement (in-
troduced in Java SE 7)—simplifies writing code in which you obtain one or more resourc-
es, use them in a try block and release them in a corresponding finally block. For
example, a file-processing application could process a file with a try -with-resources state-
ment to ensure that the file is closed properly when it's no longer needed—we demonstrate
this in Chapter 15. Each resource must be an object of a class that implements the Auto-
Closeable interface, and thus provides a close method. The general form of a try -with-
resources statement is
try ( ClassName theObject = new ClassName ())
{
// use theObject here
}
catch (Exception e)
{
// catch exceptions that occur while using the resource
}
where ClassName is a class that implements the AutoCloseable interface. This code creates
an object of type ClassName and uses it in the try block, then calls its close method to
release any resources used by the object. The try -with-resources statement implicitly calls
the theObject 's close method at the end of the try block . You can allocate multiple re-
sources in the parentheses following try by separating them with a semicolon ( ; ). You'll
see examples of the try -with-resources statement in Chapters 15 and 24.
11.13 Wrap-Up
In this chapter, you learned how to use exception handling to deal with errors. You learned
that exception handling enables you to remove error-handling code from the “main line”
of the program's execution. We showed how to use try blocks to enclose code that may
throw an exception, and how to use catch blocks to deal with exceptions that may arise.
You learned about the termination model of exception handling, which dictates that
after an exception is handled, program control does not return to the throw point. We dis-