Java Reference
In-Depth Information
20.7. Working with Files
The
java.io
package provides a number of classes that help you work
with files in the underlying system. The
File
stream classes allow you to
read from and write to files and the
FileDescriptor
class allows the sys-
tem to represent underlying file system resources as objects.
RandomAc-
cessFile
lets you deal with files as randomly accessed streams of bytes
or characters. Actual interaction with the local file system is through
the
File
class, which provides an abstraction of file pathnames, includ-
ing path component separators, and useful methods to manipulate file
names.
20.7.1.
File
Streams and
FileDescriptor
The
File
streams
FileInputStream
,
FileOutputStream
,
FileReader
, and
FileWriter
allow you to treat a file as a stream for input or output. Each
type is instantiated with one of three constructors:
•
A constructor that takes a
String
that is the name of the file.
•
A constructor that takes a
File
object that refers to the file (see
Section 20.7.3
on page
543
).
•
A constructor that takes a
FileDescriptor
object (see below).
If a file does not exist, the input streams will throw a
FileNotFoundExcep-
tion
. Accessing a file requires a security check and a
SecurityException
is
thrown if you do not have permission to access that filesee "
Security
" on
page
677
.
With a byte or character output stream, the first two constructor types
create the file if it does not exist, or truncate it if it does exist. You can
control truncation by using the overloaded forms of these two construct-
ors that take a second argument: a
boolean
that, if
true
, causes each in-
dividual write to append to the file. If this
boolean
is
false
, the file will be
