Java - File Input Output Concepts

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

2. 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

3. 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
3Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

4. 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

5. 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.
5Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

6. File Properties
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7. 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.
7Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

8. Directory Properties
8Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

9. 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

10. 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.
10Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

11. 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
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12. Byte Stream Classes
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13. Character Stream Classes
13Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

14. 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"
14Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

15. 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
15Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

16. Methods Defined by InputStream
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17. 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.
17Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

18. 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
18Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

19. Methods Defined by OutputStream
19Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

20. 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
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21. FileInputStream
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22. FileOutputStream
22Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

23. 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
23Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

24. Methods Defined by Reader
24Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

25. Reader – Subclass hierarchy
Reader
BufferedReader
InputStreamReader
StringReader
CharArrayReader
PipedReader
FilterReader
25Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

26. 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
26Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam

27. Methods Defined by Writer
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28. Writer – Subclass hierarchy
Writer
BufferedWriter
OutputStreamWriter
StringWriter
CharArrayWriter
PipedWriter
FilterWriter
PrintWriter
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29. FileReader
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30. FileReader
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The End…
Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam