COM214J2: Introduction to Programming Week 5 File IO

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COM214J2 Introduction to ProgrammingWeek 5File
I/O

• Sarabjot Singh Anand
• 16E17
• ss.anand_at_ulster.ac.uk
• http//www.infc.ulst.ac.uk/cgi-bin/infdb/homePage?
  emailss.anand_at_ulster.ac.uk

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I/O Streams

• Model interactions between the program and data
• Implemented in the java.io package
• Allow the programmer to
• Create Input Streams to read data form any data
  source
• Create Output Stream to write data to any storage
  media
• Stating the Obvious To use these Streams you
  must import the java.io package (import
  java.io.) or specific classes (import
  java.io.FileInputStream)

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The java.io Package

• Consists of a number of classes representing
  input and output streams
• Byte Streams handles bytes, integers and other
  simple data types
• FileInputStream
• FileOutputStream
• Character Streams handle text files and other
  text sources
• Object Streams handle input/output of Objects

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Byte Stream Constructors

• FileInputStream
• FileOutputStream

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Byte Streams Usage

• FileInputStream
• FileOutputStream

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import java.io. public class ReadBytes
public static void main(String
arguments) try FileInputStream file
new FileInputStream(class.dat) FileOutputStr
eam outFile new FileInputStream(outClass.dat)
boolean eof false int count
0 while (!eof) int input
file.read() System.out.print(input
) outFile.write(input) if (input
-1) eof true else count
file.close() outFile.close() System.out.p
rintln(\nBytes read count) catch
(IOException e) System.out.println(Error ..
e.toString())
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Filtering a Stream

• A filter modifies the way an existing stream is
  handled
• BufferedInputStream/ BufferedOutputStream
• Rather than writing each character to the disk,
  it buffers the data and occasionally writes to
  disk when the buffer is full or when the stream
  in flushed
• DataInputStream/ DataOutputStream
• readBoolean(), readByte(),readLong(),
  readShort(), readInt(), readFloat(), readDouble()
• Corresponding write() methods

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Declaring Streams with Filters
FileInputStream file new FileInputStream(class.
dat) BufferedInputStream buffer new
BufferedInputStream(file) DataInputStream
dataBuffer new DataInputStream(buffer)   int i
dataBuffer.readInt()
Buffered Input Stream
File Input Stream
Data Input Stream
Java Program
Data Source
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Character Streams

• Used to work with any text that is represented by
  the ASCII or Unicode character sets
• Should be used in all text input output rather
  than using the byte streams
• Subclasses of Reader and Writer classes in
  java.io
• Examples FileReader and FileWriter

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Character Stream Constructors

• FileReader
• FileWriter

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Character Stream Usage

• public int read() throws IOException
• Read a single character
• Returns
• The character read, or -1 if the end of the
  stream has been reached
• public int read(char  cbuf, int offset,
  int length) throws IOException
• Read characters into a portion of an array
• Parameters
• cbuf - Destination buffer
• offset - Offset at which to start storing
  characters
• length - Maximum number of characters to read
• Returns
• The number of characters read, or -1 if the end
  of the stream has been reached

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Character Stream Filters

• Buffered Reader/Buffered Writer

FileReader file new FileReader(myFile.txt) B
ufferedReader buffFile new BufferedReader(file)
  String Line BuffFile.readLine()
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import java.io. public class fileio
public static void main (String args)
String line String file "C\\Sarab\\teaching
\\students\\COM214J2 \\Assignment\\2004\\data.txt
" try FileReader fr new FileReader
(file) BufferedReader inFile new
BufferedReader (fr) while ((line
inFile.readLine()) ! null) System.out.println(
line) catch (IOException exception) exc
eption.printStackTrace()