Java Reference
In-Depth Information
copy()
methodends(normallyorviaathrownexception),
fis
'sand
fos
's
close()
methodsarecalled,butintheoppositeordertowhichtheseresourceswerecreated(
fis
was created before
fos
). Hence,
fos.close()
is called before
fis.close()
.
Supposethat
fos.write(buffer, 0, n)
throwsan
IOException
instance.
Now suppose that the behind-the-scenes
fos.close()
method call results in a
thrown
IOException
instance.Thislatterexceptionissuppressed,andtheexception
thrownby
fos.write(buffer, 0, n)
istheexceptionthrownoutofthe
copy()
method.Thesuppressedexceptioncanberetrievedbycalling
Throwable
's
Throw-
able[] getSuppressed()
method, which I previously presented.
Note
Atry-with-resourcesstatementcanincludecatchandfinally.Theseblocksare
executed after all declared resources have been closed.
To take advantage of try-with-resources with your own classes, keep in mind that
a resource class must implement the
java.lang.AutoCloseable
interface or its
java.lang.Closeable
subinterface.Eachinterfaceprovidesa
close()
method
that performs the close operation.
Unlike
Closeable
's
close()
method, which is declared to throw only
IOEx-
ception
(orasubtype),
AutoCloseable
's
close()
methodisdeclaredtothrow
Exception
.Asaresult,classesthatimplement
AutoCloseable
,
Closeable
,or
asubinterfacecandeclaretheir
close()
methodstothrowanykindofexception.The
close()
method should be declared to throw a more specific exception, or (as with
java.util.Scanner
's
close()
method)tonotthrowanexceptionifthemethod
cannot fail.
Note
Implementationsof
Closeable
's
close()
methodare
idempotent
;subse-
quentcallsto
close()
havenoeffectontheresource.Incontrast,implementationsof
AutoCloseable
's
close()
methodarenotrequiredtobeidempotent,butmaking
them idempotent is recommended.
Assertions
Writingsourcecodeisnotaneasytask.Alltoooften,
bugs
(defects)areintroducedinto
the code. When a bug is not discovered before compiling the source code, it makes it
intoruntimecode,whichwillprobablyfailunexpectedly.Atthispoint,thecauseoffail-
ure can be very difficult to determine.
Developers often make assumptions about application correctness, and some deve-
lopers think that specifying comments that state their beliefs about what they think is
