JAVA

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References

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I/O Streams in Java
Introduction - 1

• Definition
• Stream is a flow of Data.
• characters read from a file
• bytes written to the network
• The information can be read/written sequentially
  from/to the stream.
• The assumption made on the stream the
  information passes in FIFO order.

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Introduction - 2

• No matter where the data is coming from or going
  to and no
• matter what its type, the algorithms for
  sequentially reading
• and writing data are basically the same

Reading
Writing
open a stream while more information write
information close the stream
open a stream while more information read
information close the stream
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Standard Input / Output Streams in Java
Writing to the screen System.out.print() System
.out.println()
Reading from the screen System.in.read(byte) S
ystem.in.read(byte,int,int)

• Standard streams are automatically opened, so
  no need to
• open them explicitly.
• Writing System.out.print(Hello\n) is the same
  as writing
• System.out.println(Hello)
• You have to create byte array before calling
  read function.
• read function has to be surrounded by try
  catch(..)
• block.

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Example - Echo
package test import java.io. public class
IOTest public IOTest() public static
void main(String args) byte ch new
byte80 int num 0 try
num System.in.read(ch)
System.out.println(new String(ch,0,num)) //
String(byte bt, int offset,int length)
catch (IOException ex)
System.out.println("Can't read")
ex.printStackTrace()
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java.io Classes Hierarchy

• The Streams can be divided into Character Streams
  and Byte Streams
• Character Streams
• Reader and Writer are the abstract superclasses
  for character streams in java.io. Reader provides
  the API and partial implementation for
  readers--streams that read 16-bit characters--and
  Writer provides the API and partial
  implementation for writers--streams that write
  16-bit characters.
• Byte Streams
• To read and write 8-bit bytes, programs should
  use the byte streams, descendants of InputStream
  and OutputStream . InputStream and OutputStream
  provide the API and partial implementation for
  input streams (streams that read 8-bit bytes) and
  output streams (streams that write 8-bit bytes).
  These streams are typically used to read and
  write binary data such as images and sounds.

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Character Streams Hierarchy
BufferedReader
LineNumberReader
CharArrayReader
InputStreamReader
FileReader
Reader
FilterReader
PushbackReader
PipedReader
StringReader
BufferedWriter
CharArrayWriter
OutputStreamWriter
FileWriter
Writer
FilterWriter
PipedWriter
StringWriter
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Example
import java.io. //must be imported public
class Copy public static void main(String
args) throws IOException File inputFile new
File("farrago.txt") File outputFile new
File("outagain.txt") //FileOutputStream and
FileInputStream for bytes //throws
FileNotFoundException (descendent of
IOException) FileReader in new
FileReader(inputFile) FileWriter out new
FileWriter(outputFile) int c
while ((c in.read()) ! -1)
out.write(c) // housekeeping in.close()
out.close()
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Advanced Usage
//extracts from a class not a whole
class//args ltname of filegtltname of
delimitergt import java.io. import
java.util.StringTokenizer . . . try int
lineNum, wordNum String line
BufferedReader inStream new BufferedReader(new
FileReader(args0)) lineNum wordNum
0 do line inStream.readLine()
if(line ! null)
lineNum StringTokenizer st new
StringTokenizer(line,args1) wordNum
st.countTokens()
while(line ! null) System.out.println("Th
ere are " lineNum " lines.")
System.out.println("There are " wordNum "
words.") catch(FileNotFoundException fnfe)
System.out.println("File (" args0 ") not
found.") catch(IOException ioe)
System.out.println("I/O error while reading file
(" args0 ")")
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private void writeToFile(String from, String
to) try FileReader fr new
FileReader(from) BufferedReader br new
BufferedReader(fr) FileWriter fw new
FileWriter(to) String line null, srt
String wline int lineNum wordNum 0
while ( (line br.readLine()) ! null )
str line.split("\\s") wordNum
str.length lineNum
fw.write("There are " lineNum " lines.")
fw.write("There are " wordNum " words.")
fw.close() fr.close() catch
(IOException e) System.out.println("Uh oh,
got an IOException error!")
e.printStackTrace()
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IO - Advanced topics

• Redirecting standard IO
• System contains setIn, setOut and setErr.
• System.setIn(new FileInputStream(x.dat))
• System.setOut(new PrintStream(new
  FileOutputStream( "out.txt")))
• Standard streams could be from/to anything you
  want!
• Compression
• Read about ZipInputStream and ZipOutputStream
• For more information
• jdk documentation
• On-line tutorials http//java.sun.com/docs/books
  /tutorial/