Java Reference
In-Depth Information
System.exit(1);
}
// Get the channel for the file
FileChannel outputChannel = outputFile.getChannel();
The
FileChannel
class implements all of the channel interfaces that we discussed in the previous
section, so any
FileChannel
object incorporates the methods we have seen for both reading and
writing a file. However, a
FileChannel
object obtained from a
FileOutputStream
object will not
be able to read from the file since the stream only permits output. Similarly, a
FileChannel
obtained
from a
FileInputStream
object can only read from the file. If you try to perform a read operation on
a file opened just for output, a
NonReadableChannelException
will be thrown. Attempting to write
to a file opened for input will result in a
NonWritableChannelException
being thrown.
Once you have obtained a reference to a file channel, you are ready to read from or write to the file, but
we need to learn a bit more about buffers before we can try that out.
Buffers
All the classes that define buffers have the abstract class
Buffer
as a base. The
Buffer
class therefore
defines the fundamental characteristics common to all buffers. A particular buffer can store a sequence of
elements of a given type, and an element can be of any primitive data type other than
boolean
. Thus, you
can create buffers to store
byte
values,
char
values,
short
values,
int
values,
long
values,
float
values,
or
double
values. The following classes in the
java.nio
package define these buffers:
Class
Description
ByteBuffer
A buffer that stores elements of type
byte
. You can also store the
binary values of any of the other primitive types in this buffer,
except for type
boolean
. Each binary value that you store will
occupy a number of bytes in the buffer determined by the type -
values of type
char
or
short
will occupy two bytes,
int
values will
occupy four bytes, and so on. Only buffers of this type can be used
in a file I/O operation.
CharBuffer
A buffer that only stores elements of type
char
.
ShortBuffer
A buffer that only stores elements of type
short
.
IntBuffer
A buffer that only stores elements of type
int
.
LongBuffer
A buffer that only stores elements of type
long
.
FloatBuffer
A buffer that only stores elements of type
float
.
DoubleBuffer
A buffer that only stores elements of type
double
.
