42:I/O operations in JAVA

Learning Objectives
After completing this session, you will be able to:
‰  Define an I/O stream
‰  Identify the types of streams
‰  Explain the Stream class hierarchy
I/O Streams
‰  An I/O Stream represents an input source or an output destination.
‰  A stream can represent many different kinds of sources and destinations like disk files,
devices, other programs, a network socket, and memory arrays.
‰  Streams support many different kinds of data like simple bytes, primitive data types,
localized characters, and objects.
‰  Some streams simply pass on data, others manipulate and transform the data in
useful ways.
‰  No matter how they work internally, all streams present the same simple model to
programs that use them. A stream is a sequence of data.
Input Stream
A program uses an input stream to read data from a source, one item at a time.

 Output Stream
A program uses an output stream to write data to a destination, one item at time.

 General Stream Types
The general stream types are:
‰  Character and Byte Streams: Character streams are the streams that read and write
16-bit characters whereas Byte streams are the streams that read and write 8-bit
bytes.
‰  Input and Output Streams: Based on source or destination
‰  Node and Filter Streams: Whether the data on a stream is manipulated or transformed
or not.
Character and Byte Streams
‰  Byte streams:For binary data
‰  Root classes for byte streams:
oThe InputStream class
oThe OutputStream class
oBoth classes are abstract
‰  Character streams:For Unicode characters
‰  Root classes for character streams:
oThe Reader class
oThe Writer class
oBoth classes are abstract
Input and Output Streams
‰  Input or source streams: Can read from these streams
‰  Root classes of all input streams:
oThe InputStream class
oThe Reader class
‰  Output or sink (destination) streams: Can write to these streams
‰  Root classes of all output streams:
oThe OutputStream class
oThe Writer class
Node and Filter Streams
‰  Node streams (Data sink stream):Contain the basic functionality of reading or
writing from a specific location
‰  Types of node streams include files, memory, and pipes
‰  Filter streams (Processing stream):Layered onto node streams between threads or
processes
‰  For additional functionality like altering or managing data in the stream
‰  Adding layers to a node stream is called stream chaining
Streams
Streams are shown in the following diagram:

Tips and Tricks:
‰  How many bits are used torepresent Unicode, ASCII, UTF-16, and UTF-8 characters?
‰  What is the default character encoding of your platform?
Solution:
‰  Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set
uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using
8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.
‰  If you are running Java on English Windows platforms, then it is probably Cp1252. If
you are running Java on English Solaris platforms, then it is most likely 8859_1.
Summary
‰  The central building block of the Java I/O framework is the stream. “A stream is a
flowing sequence of characters”.
‰  In other words, a stream is usually considered to be an abstraction for the capability to
move bytes from a source to a sink.
‰  Input operations begin by openinga stream from the source and using a read()
method to obtain the data via the stream. Similarly, output operations begin by
opening a stream to the destination and using a write() method to send the data.
‰  The package named java.iocontains a set of input and output stream classes that can
be used to read and write data.
‰  The java.iopackage also provides specialized InputStream and OutputStream
subclasses that are used for specialized types of input and output.
‰  The InputStream class and OutputStream class are abstract superclasses that define
the behavior for sequential input and output streams in Java.
‰  Classes in java.iopackage are designed to be “chained” or “wrapped”. (This is a
common use of the decorator design pattern.)
Test Your Understanding
1.What is a ‘stream’?
2.Name some important input and output stream classes.
3.OutputStream and InputStreamclasses serve as the base classes for all byte stream
classes. Comment on this statement.