Java InputOutput

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Java Input/Output

• Dave Elliman

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I/O Streams

• Java I/O is accomplished using objects that
  represent streams of data
• A stream is a sequence of bytes that flow from a
  source to a destination. In Java a character is
  unicode or 2 bytes.
• In a program, we read information from an input
  stream and write information to an output stream

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I/O Streams

• The java.io package contains many classes that
  allow us to define various streams with
  particular characteristics
• Some classes assume that the data consists of
  characters
• Others assume that the data consists of raw bytes
  of binary information

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The IOException Class

• Operations performed by the I/O classes may throw
  an IOException
• Most likely because a file intended for reading
  or writing might not exist
• You need a try/catch statement
• try catch(Excepyion e)

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Standard I/O Data Streams

• There are three standard I/O streams
• standard input defined by System.in
• standard output defined by System.out
• standard error defined by System.err
• System.in typically represents keyboard input
• System.out and System.err typically represent a
  particular window on the monitor screen
• We use System.out when we execute println
  statements

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Standard Input

• InputStreamReader stdin new InputStreamReader(Sy
  stem.in)
• BufferedReader in new BufferedReader(stdin)
• String name in.readLine()
• InputStreamReader converts the byte input stream
  to a character input stream
• BufferedReader allows us to use the readLine
  method to get an entire line of input

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Standard I/O example

• import java.io.
• public class TestIO
• public static void main(String args)
• double x
• String y
• BufferedReader in
• new BufferedReader(new
  InputStreamReader(System.in))
• try
• System.out.print(Enter a floating
  point value )
• x Double.parseDouble(in.readLine())
  
• System.out.print(Enter some text
  )
• y in.readLine()
• System.out.println(x y)

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Text Files

• Information can be read from and written to text
  files by declaring and using the correct I/O
  streams
• The FileReader class represents an input file
  containing character data
• The FileWriter class represents a text output
  file, but with minimal support for manipulating
  data
• Therefore use the PrintWriter class provides
  print and println methods

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Text File I/O Streams

• Input
• BufferedReader in new BufferedReader(newFileRead
  er(in.txt))
• In Java 1.5 the Scanner class makes life easier
  java.util.Scanner
• Output
• PrintWriter out new PrintWriter(new
  FileWriter(out.txt"))
• streams should be closed explicitly
• out.close()

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That is all you need for PRG

• But
• You might like to learn about reading and writing
  binary files
• Why not find out about reading and writing
  objects to file. This is known as serialization