Java - File Input Output Concepts

Java - File Input / Output
Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

Topics
 Input/output
 File
 Directories
 The Stream Classes
 IO Stream Types
 Binary Versus Text Files
 Byte Streams - InputStreams
 Byte Streams - OutputStreams
 Character Streams - Reader
 Byte Streams - Writer
2Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

Input/output
 Java programs perform I/O through streams.
 A stream is an abstraction that either produces or
consumes information.
 A stream is a sequence of bytes (or data or objects) that
flow from a source to a destination.
 A stream is linked to a physical device by the Java I/O
system.
 Stream: an object that either,
 sends data to its destination (screen, file, etc.) or
 accepts data from a source (keyboard, file, etc.)
 acts as a transmission/exchange buffer between source and
destination
 Java implements streams (IO operations) within class
hierarchies defined in the java.io package.
https://docs.oracle.com/javase/7/docs/api/java/io/package-summary.html

File
 We begin our discussion with one of the most distinctive
I/O classes: File.
 Although most of the classes defined by java.io operate
on streams, the File class does not.
 It deals directly with files and the file system.
 That is, the File class does not specify how information is
retrieved from or stored in files; it describes the
properties of a file itself.
 A File object is used to obtain or manipulate the
information associated with a disk file, such as the
permissions, time, date, and directory path, and to
navigate subdirectory hierarchies.
 Files are a primary source and destination for data within
many programs. 4Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

File
 A directory in Java is treated simply as a File with one
additional property — a list of filenames that can be
examined by the list( ) method.
 The following constructors can be used to create File
objects:
 File(String directoryPath)
 File(String directoryPath, String filename)
 where, directoryPath is the path name of the file, filename is the
name of the file or subdirectory,
 File defines many methods that obtain the standard
properties of a File object.
 For example,
 getName( ) returns the name of the file,
 getParent( ) returns the name of the parent directory,
 and exists( ) returns true if the file exists, false if it does not.

File Properties

Directories
 A directory is a File that contains a list of other files and
directories.
 When you create a File object and it is a directory, the
isDirectory( ) method will return true.
 In this case, you can call list( ) on that object to extract
the list of other files and directories inside.

Directory Properties

The Stream Classes
 There are two type of stream:
 Input stream receives data from a source into a program.
 Output stream sends data to a destination from the
program.
 Standard input/output stream in Java is represented by
three fields of the System class : in, out and err.
Input Stream Output Stream
Reading:
open a stream
while more information
read information
close the stream
Writing:
open a stream
while more information
write information
close the stream 9Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

IO Stream Types
 Two main categories of streams in Java :
 Byte Streams –
 These provide a way to handle byte oriented
input/output operations.
 InputStream and OutputStream classes are at the
top of their hierarchy.
 Each of these abstract classes has several concrete
subclasses that handle the differences between
various devices, such as disk files, network
connections, and even memory buffers.
 Two of the most important are read( ) and write( ),
which, respectively, read and write bytes of data.

IO Stream Types
 Two main categories of streams in Java :
 Character Streams –
 These provide a way to handle character oriented
input/output operations.
 At the top are two abstract classes, Reader and
Writer
 They make use of Unicode and can be
internationalized.
 Two of the most important methods are read( ) and
write( ), which read and write characters of data,
respectively.
 These methods are overridden by derived stream
classes

Byte Stream Classes

Character Stream Classes

Binary Versus Text Files
 Binary files: the bits represent other types of encoded
information, such as executable instructions or numeric
data
 these files are easily read by the computer but not
humans
 they are not "printable" files
 actually, you can print them, but they will be
unintelligible
 Text files: the bits represent printable characters
 one byte per character for ASCII, the most common
code
 for example, Java source files are text files
 so is any file created with a "text editor"

Byte Streams - InputStreams
 InputStream is an abstract class that defines Java’s model
of streaming byte input.
 Most of the methods in this class will throw an IOException
on error conditions.
 Reading bytes:
 Used to read 8-bit bytes
 Classes of hierarchy of input stream classes
 Input Functions
 Reading bytes
 Closing streams
 Marking positions in stream
 Skipping in a stream
 Finding the number of bytes in a stream

Methods Defined by InputStream

InputStream – Subclass hierarchy
InputStream
AudioInputStream
FileInputStream
ObjectInputStream
SequenceInputStream
ByteArrayInputStream
PipedInputStream
FilterInputStream
A FileInputStream
obtains input bytes
from a file in a file
system.
An AudioInputStream is
an input stream with a
specified audio format
and length.
A ByteArrayInputStream
contains an internal
buffer that contains
bytes that may be read
from the stream.
A SequenceInputStream
represents the logical
concatenation of other
input streams.

Byte Streams - OutputStreams
 OutputStream is an abstract class that defines streaming
byte output.
 Most of the methods in this class return void and throw
 an IOException in the case of errors.
 Writing bytes:
 Classes of hierarchy of Outputstream classes
 Output Functions
 Writing bytes
 Closing streams
 Flushing streams

Methods Defined by OutputStream

OutputStream – Subclass hierarchy
FileOtputStream is an
output stream for
writing data to a File.
A ByteArrayInputStream
is a output stream in
which the data is
written into a byte
array.
OutputStream
FileOutputStream
ObjectOutputStream
ByteArrayOutputStream
PipeOutputStream
FilterOutputStream

FileInputStream

FileOutputStream

Character Streams - Reader
 Reader is an abstract class that defines Java’s model of
streaming character input.
 All of the methods in this class will throw an IOException
on error conditions.
 Reading character:
 Used to read characters from the files
 Classes of hierarchy of reader class
 Functions are similar to InputStream

Methods Defined by Reader

Reader – Subclass hierarchy
Reader
BufferedReader
InputStreamReader
StringReader
CharArrayReader
PipedReader
FilterReader

Byte Streams - Writer
 Writer is an abstract class that defines streaming character
output.
 All of the methods in this class throw an IOException
 in the case of errors.
 Writing characters:
 Classes of hierarchy of writer class
 Output Functions
 Writing bytes
 Closing streams
 Flushing streams

Methods Defined by Writer

Writer – Subclass hierarchy
Writer
BufferedWriter
OutputStreamWriter
StringWriter
CharArrayWriter
PipedWriter
FilterWriter
PrintWriter

FileReader

31
The End…
Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

Java - File Input Output Concepts

Recommended

More Related Content

What's hot (20)

Similar to Java - File Input Output Concepts (20)

More from Victer Paul (13)

Recently uploaded (20)

Java - File Input Output Concepts