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C H A P T E R

The Package

java.io

I

NPUT and output in Jav

The P

a is or

ackage java.io

ganized around the concept of streams. A stream

is a sequence of items, usually 8 bit bytes, read or written over the course of time.

In the

java.io

 package, all input is done through subclasses of the abstract

class

InputStream

, and all output is done through subclasses of the abstract class

OutputStream

. The one exception to this rule is the class

RandomAccessFile

,

which handles files that allow random access and perhaps intermixed reading and

writing of the file.

For an input stream, the source of data might be a file, a

String

, an array of

bytes, or bytes written to an output stream (typically by another thread). There are

also  filter input streams  that take data from another input stream and transform

or augment the data before delivering it as input. For example, a

LineNumberInputStream

passes bytes through verbatim but counts line termina 

tors as they are read.

For an output stream, the sink of data might be a file, an array of bytes, or a

buffer to be read as an input stream (typically by another thread). There are also

 filter output streams  that transform or augment data before writing it to some

other output stream.

An instance of class

File

 represents a path name (a string) that might identify

a particular file within a file system. Certain operations on the file system, such as

renaming and deleting files, are done by this class rather than through streams.

An instance of class

FileDescriptor

 represents an abstract indication of a

particular file within a file system; such file descriptors are created internally by

the Java I/O system.

There are two interfaces,

DataInput

 and

DataOutput

, that support the trans 

fer of data other than bytes or characters, such as long integers, floating point

numbers and strings. The class

DataInputStream

 implements

DataInput

; the

class

DataOutputStream

 implements

DataOutput

; and

RandomAccessFile

implements both

DataInput

 and

DataOutput

.

The class

StreamTokenizer

 provides some simple support for parsing bytes

or characters from an input stream into tokens such as identifiers, numbers, and

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