UNIT:6

FILE HANDLING
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TOPICS TO BE COVERED
 6.1 Stream classes, class hierarchy, useful I/O
classes, creation of text file, reading and writing
text files

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 INTRODUCTION

When we use variables and array for storing data inside the
programs. We face two Problems:

1) The data is lost either when a variable goes out of scope or when
the program is terminated. The storage is temporary.

2) It is difficult to handle large volumes of data using variables and

arrays.

 We can overcome these problems by storing data into secondary

storage devices. We can store data using concept of files. Data
stored in file is often called persistent data.

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 A file is collection of related records placed area on the disk. A
record is composed of several fields. Field is a group of
characters.

 Storing and managing data using file is known as file

processing which includes tasks such as creating files,
updating files and manipulation of data.

 Reading and writing of data in a file can be done at the level of

bytes or characters or fields depending on the requirement of
application.java provides capabilities to read and write class
object directly.

 The process of reading and writing objects is called

serialization.

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CONCEPT OF STREAM
 In file processing, input refers to the flow of data into a program
and output means the flow of data out of a program.

 Input to a program may come from the keyboard, mouse,

memory, disk a network or another program.

 Output from a program may go to the screen, printer, memory

disk, network or another program.

 Input and output share certain common characteristics like

unidirectional movement of data, treating data as a sequence of
bytes or characters and support to sequential access to data.

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 Java uses concept of stream to represent ordered sequence
of data, a common characteristics shared by all
input/output devices.

 A stream presents uniform, easy to use, object oriented

interface between the program and the input/output
devices.

 A stream in java is a path along which data flows (like pipe

along which water flows). It has source (of data) and
destination (for that data).

 Both the source and destination may be physical devices or

programs or other streams in same program

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 The concept of sending data from one stream to another has
made streams in java a powerful tool for file processing.

 We can build a complex file processing sequence using a

series of simple stream operation.

 This feature is used to filter data along the pipeline of

streams so that we obtain data in desired format.

 Java stream classified into basic type as follow:

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 Stream

Input Stream Output Stream

Input stream: it extracts (i.e. reads) data from the source (file) and sends it
to the program.

Output stream: it takes data from the program and sends (i.e. writes) it to
the destination (file).

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 Input stream
Reads
source Program

(a) Reading data into a program

Output stream
Writes
Program Destination

(b) Writing data to a destination

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 keyboard
standard input
stream

CPU

standardout
put stream MEM

monitor
terminal file
console input
stream
LOAD
READ HDD
What does information travel across?

Streams files

file output
stream
SAVE10
WRITE
STREAM CLASSES
The java.io package contains a large number of stream classes
that provide capabilities for processing all types of data.

The classes may be categorized into two groups based on the

data type on which they operate.

1. Byte stream classes that provides support for handling I/O

operations on bytes.

2. Character stream classes that provide support for managing

I/O operation on characters

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 These groups may further be classified based on their functions.

 Byte stream and character stream classes contain specialized

classes to deal with input and output operations independently on
various type of devices.

 We can also cross-group the streams based on the type of source

or destination they from or write to.

 The source (or destination) may be memory, a file or a pipe.

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1) Byte stream classes
 Byte stream classes have been designed to provide functional
features for creating and manipulating streams and files reading
and writing bytes.

 Since the steams are unidirectional, they can transmit bytes in

only one direction and, therefore, Java provides two kinds of byte
stream classes:
1) input stream classes
2) output stream classes.

Input Stream Classes

 Input stream classes that are used to read 8-bit bytes include
super class known as InputStream and a number of subclasses
for supporting various input-related functions.
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 The super class InputStream is an abstract class, and,
therefore, we cannot create instances of this class.

 Rahter,we must use the subclasses that inherit from this

class.

 The InputStream class defines method for performing input

functions such as
 Reading bytes
 Closing streams
 Marking position in streams
 Skipping ahead in a stream
 Finding the number of bytes in a stream
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 Method Description
1 read() Reads a byte from the input stream

2 read(byte b[]) Reads an array of bytes into b

3 read(byte b[],int n,int m) Reads m bytes into b starting from
nth byte

4 available() Gives number of bytes available in

the input

5 skip(n) Skips over n bytes from the input

stream

6 reset() Goes back to the beginning of the

stream
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7 close() Closes the input stream.

 Note that the class DataInputStream extends
FilterInputStream and implements the interface DataInput.

 Therefore, the DataInputStream class implements the methods

described in DataInput in addition to using the method of
InputStream class.

 The DataInput interface contains the following method.

 readShort()
 readInt()
 readLong()
 readFloat()
 readUTF()
 readDouble()
 readLine()
 readChar()
 readBoolean() 18
OUTPUT STREAM CLASSES
 Output stream classes are derived from the base class
OutputStream as shown in figure.

 Like InputStream, the OutputStream is an abstract class and

therefore we cannot instantiate it. The several subclasses of the
OutputStream can be used for performing the output operations.

 The OutputStream includes methods that are designed to

perform the following task:
 Writing bytes
 Closing stream
 Flushing stream

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 Method Description
1 write() Writes a byte to the output
stream

2 write(byte b[]) Writes all bytes in the array b to

the output stream

3 write(byte b[],int n,int m) Writes m bytes from array b

starting from nth byte

4 close() Close the output stream

5 flush() Flushes the output stream

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 The DataOutputStream, a counterpart of DataOutputStream,
implements the interface DataOutputStream .

 Therefore ,implements the following method contained in

DataOutput interface.
 writeShort()
 writeInt()
 writeLong()
 writeFloat()
 writeUTF()
 writeDouble()
 writeBytes()
 writeChar()
 writeBoolean()

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CHARACTER STREAM
CLASSES

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 CHARACTER STREAM CLASSES
 Character stream classes were not a part of the language when it
was released in 1995.

 They were added later when the version 1.1 was announced.

 Character streams can be used to read and write 16-bit Unicode

characters.

 Like byte streams, there are two kinds of character stream

classes
1) reader stream classes
2) writer stream classes.

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READER STREAM CLASSES
 Reader stream classes are designed to read character from the
files. Reader class is the base class for all other classes in this
group as shown in figure.

 These classes are functionally very similar to the input stream

classes, except input stream use bytes as their fundamental unit
of information, while reader stream use characters.

 The Reader class contains method they are identical to those

available in the InputStream class, except Reader is designed to
handle characters. Therefore, reader classes can perform all the
functions implemented by the input stream classes.

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 WRITER STREAM CLASSES
 Like output stream classes, the writer stream classes are
designed to perform all output operations on files.

 Only difference is that while output stream classes are designed

to write bytes, the writer stream classes are designed to write
characters.

 The Writer class is an abstract class which acts as a base class

for all other writer stream classes .

 This base class provides support for all output operations by

defining method that are identical to those in OutputStream
class.

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USING STREAMS
 We have types of input and output stream classes used for
handling both the 16-bit characters and 8-bit bytes. Although
all the classes are known as i/o classes, not all of them are
used for reading and writing operations only.

 Some perform operations such as buffering, filtering, data

conversion, counting and concatenation while carrying out
I/O tasks.

 As pointed out earlier, both the character stream group and

the byte stream group contain parallel pairs of classes that
perform the same of operations but for the different data
type.

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 Task Character Stream Byte Stream Class
Class
Performing input Reader InputStream
operations
Buffering input BufferedReader BufferdInputStream
Keeping track of LineNumberReader LineNumberInputStream
line numbers
Reading from an CharArrayReader ByteArrayInputStream
array
Translating byte InputStreamReader (none)
stream into a
character stream
Reading from files FileReader FileInputStream
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Filtering the input FilterReader FilterInputStream
 Task Character Byte Stream Class
Stream Class
Pushing back PushbackReader PushbackInputStream
characters/bytes
Reading from a pipe PipedReader PipedInputStream
Reading from a StringReader StringBufferInputStream
string
Reading primitive (none) DataInputStream
types
Performing output Writer OutputStream
operations
Buffering output BufferedWriter BufferedOutputStream
Writing to an array CharArrayWriter ByteArrayOutputStream 31
 Task Character Byte Stream Class
Stream Class
Filtering the output FilterWriter FilterOutputStream
Translating OutputStreamWri (none)
character stream ter
into a byte stream
Writing to a file FileWriter FileOutputStream
Printing values and PrintWriter PrintStream
objects
Writing to a pipe PipedWriter PipedOutputStream
Writing to a string String Writer (none)
Writing primitive (none) DataOutputStream
types 32
OTHER USEFUL CLASS
 The java.io package supports many other classes for performing
certain specialized functions. They include among others:
 RandomAccessFile :
 The RandomAccessFile enables us to read and write bytes, text
and java data types to any location in a file. This class extends
object class and implements DataInput and DataOutput
interface

 StreamTokenizer :
 The class StreamTokenizer, a subclass of object can be used
for breaking up a stream of text from an input text file into
meaningful pieces called tokens. The behaviour of the
StreamTokenizer class is similar to that of StringTokenizer
class (of java.util package) that breaks string into its component
tokens.

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 Object
interface interface

DataInput DataOutput

RandomAccessFile

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USING THE FILE CLASS
 The java.io package includes a class known as the File class
that provides support for creating files and directories. The
class includes several constructors for instantiating the File
objects.
 File class provides methods for operations like:
 Creating a file
 Opening a file
 Closing a file
 Deleting a file
 Getting the name of a file, Getting the size of a file
 Checking the existence of a file
 Renaming a file
 Checking whether the file is writable
 Checking whether the file is readable
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 INPUT/OUTPUT EXCEPTIONS
 When creating files and performing I/O operations on them, the system
may generate I/O related exceptions. The basic I/O related exception
classes and their functions:

I/O exception class Function

EOFException Signals that an end of file or end of
stream has been reached
unexpectedly during input
FileNotFoundExcepti Informs that a file could not be
on found
InteruuptedIOExcepti Warns that an I/O operations has
on been interrupted
IOException Signals that an I/O exception of
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some sort has occurred
CREATION OF FILES
 If we want to create and use a disk file, we need to decide the
following about the file and its intended purpose:
 Suitable name for the file.
 Data type to be stored.
 Purpose (reading, writing, or updating).
 Method of creating the file.

 A filename is a unique string of character that helps identify a

file on the disk. The length of a filename and the characters
allowed are dependent on the OS on which the java program is
executed.
 A filename may contain two parts, a primary name and an
optional period with extension.

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 Data type is important to decide the type of file stream classes to
be used for handling the data. We should decide whether the data
to be handled is in the form of characters, bytes or primitive type.

 The purpose of using a file must also be decided before using it. For
example, we should know whether the file is created for reading
only, or both the operations.

 As we know, for using a file, it must be opened first. This is done by

creating a file stream and then linking it to the filename.

 A file stream can be defined using the class of

Reader/InputStream for reading data and
Writer/OutputStream for writing data.

 The common stream classes used for various i/o operations given in
table . The constructors of stream classes may be used to assign the
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desired filenames to the Stream objects.
Source/destination Characters
Read Write
Memory CharArrayReader CharArrayWriter
File FileReader FileWriter
Pipe PipedReader PipedWriter

Source/destination Bytes
Read Write
ByteArrayOutputStrea
Memory ByteArrayInputStream
m
File FileInputStream FileoutputStream
Pipe PipedInputStream PipedoutputStream
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 There are two ways of Italianizing the file Stream objects.

 All of the constructors require that we provide the name of

the file either directly or indirectly by giving a file object
that has already assigned a file name

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DIRECT CREATION
FileInputStream fis;
try
{
//Assign the filename to the file stream object
fis = new FileInputStream (“test.txt”);
........
}
catch (IOException e)
...........
...........

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 INDIRECT CREATION
.............
File inFile;
InFile = new file (“test.txt”);
FileInputStream fis;
try
{
//give the value of the file object
//to the file stream object
Fis=new FileInputStream (inFile);
..............
}
catch (......)
{
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................
}
The code above includes five tasks:
 Select a filename.
 Declare a file object.
 Give a selected name to the file object declared.
 Declare a file stream object.
 Connect the file to the stream object.

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Reading/writing characters
 As pointed out earlier, subclass of Reader and Writer implement
streams that can handle characters.

 The two subclasses used for handling characters in files are

FileReader and FileWriter.

 The concept of using file streams and file object for reading and
writing characters in program is illustrated in fig:

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READING/WRITING BYTES:
 We have used FileReader and FileWriter classes to read
and write 16-bit characters.

 Most file systems use only 8-bit bytes.

 java i/o system provides a number of classes for handling

bytes are FileInputStream and FileOutputStream classes.

 We can use them in place of FileReader and file writer

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Thank you

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