While this
advice may seem obvious, it is violated often enough that it bears repeating.
When the designers of an API declare a method to throw an exception, they are
trying to tell you something. Don’t ignore it! It is easy to ignore exceptions
by surrounding a method invocation with a try
statement
with an empty catch block:
// Empty catch block ignores exception - Highly
suspect!
try {
...
} catch (SomeException e) {
}
An empty catch block defeats the purpose of exceptions, which is to
force you to handle exceptional conditions. Ignoring an exception is analogous
to ignoring a fire alarm—and turning it off so no one else gets a chance to see
if there’s a real fire. You may get away with it, or the results may be
disastrous. Whenever you see an empty catch
block,
alarm bells should go off in your head. At the very least, the catch block should contain a comment explaining why
it is appropriate to ignore the exception.
An example of
the sort of situation where it might be appropriate to ignore an exception is
when closing a FileInputStream. You haven’t
changed the state of the file, so there’s no need to perform any recovery
action, and you’ve already read the information that you need from the file, so
there’s no reason to abort the operation in progress. Even in this case, it is
wise to log the exception, so that you can investigate the matter if these
exceptions happen often.
The advice in
this item applies equally to checked and unchecked exceptions. Whether an
exception represents a predictable exceptional condition or a programming
error, ignoring it with an empty catch
block
will result in a program that continues silently in the face of error. The
program might then fail at an arbitrary time in the future, at a point in the
code that bears no apparent relation to the source of the problem. Properly
handling an exception can avert failure entirely. Merely letting an exception
propagate outward can at least cause the program to fail swiftly, preserving
information to aid in debugging the failure.
Reference: Effective Java 2nd Edition by Joshua Bloch
