Chapter 15 Text Processing and File InputOutput

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Chapter 15Text Processing andFile Input/Output

• Lecture Slides to Accompany
• An Introduction to Computer Science Using Java
  (2nd Edition)
• by
• S.N. Kamin, D. Mickunas, E. Reingold

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Chapter Preview

• In this chapter we will
• describe the java.io package
• introduce the Java StringBuffer class
• show how files can be read and written
• discuss how to handle file input and output
  exceptions
• demonstrate how to perform console input and
  output

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Strings

• Java provides a number of methods for operating
  on String objects
• String objects are immutable
• Immutable objects cannot be changed once they are
  created

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StringBuffer

• Java provides a mutable staring class called
  StringBuffer that allows strings to grow
  dynamically during program execution
• Several StringBuffer methods are the same as
  those found in String
• To convert between String objects and
  StringBuffer objects Java provides constructors
  for each class
• The StringBuffer class also contains a ToString
  method to allow easier output

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Sequential Files

• Files are stored are stored on disks
• In this section we will assume that files consist
  of multiple lines composed of characters
• Each line ends with an end of line character
• The file itself may have an end of file character
• Programmers often need to read or write files
  stored on disks

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File Input

• Java classes that support file input are found in
  the java.io package
• FileReader allows us to open a file for reading
• BufferedReader is a wrapper class that provides
  methods that
• allow us to treat the file as a stream of
  characters
• increases the efficiency of reading
• allows line-oriented reading

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Wrapper Classes

• Class W is said to wrap class Y if
• Y is a concrete (not abstract) class
• Ws constructor takes Y as an argument and stores
  a local copy of Y
• W reimplements all of Ys methods
• A wrapper can wrap a class and be the subclass of
  another class at the same time

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Buffered Input

• We can make a file available for reading one
  character at a time by using
• FileReader fr FileReader(filename)
• We can read the file more efficiently by reading
  a block of characters at a time, this is called
  buffering the read
• To perform a buffered read we use this
• BufferedReader br
• new BufferedReader(
• new FileReader(filename))

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Input Example Part 1

• import CSLib.
• import java.io.
• public class Copy
• // Copy file to an OutputBox
• private FileBuffer fr
• private BufferedReader br
• public Copy(String filename) throws IOException
  
• // open local file given by filename
• br new BufferedReader(new
  FileReader(filename))

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Input Example Part 2

• public void copy( ) throws IOException
• OutputBox out new OutputBox( )
• int I
• while (true)
• i br.read()
• if (i -1) // check for end of
  file
• return
• out.print((char) i) // must have char to
  print

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File Output

• Java classes that support file output are found
  in the java.io package
• FileWriter and BufferedReader provide methods to
  write
• a single character
• an array of characters
• a string
• the end of line
• PrintWriter is a wrapper class provided to
  convert several data type values to printable
  forms

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Writing to a File

• To make a file available for printing
• PrintWriter pr
• new PrintWriter(
• new BufferedWriter(
• new FileWriter(filename)))
• PrintWriter has void methods print and println
  that behave the same way as they for OutputBox
  objects

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Mail Merge Application part 1

• import java.io.
• public class MailMerge
• // mail merge application
• BufferedReader template, maillist
• PrintWriter out
• public void openFiles(String fn) throws
  Ioexception
• template new BufferedReader(
• new FileReader(fn
  .template))
• maillist new BufferedReader(
• new FileReader(fn .list))
• out new PrintWriter(
• new BufferedWriter(
• new FileReader(fn .out)))

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Mail Merge Application part 2

• private StringBuffer
• readUpto(BufferedReader br, char
  delim)
• throws
  Ioexception
• StringBuffer sb new StringBuffer( )
• int inputChar
• while (true)
• inputchar br.read( )
• if ((inputchar -1) (inputchar
  delim))
• return sb
• sb.append((char) inputchar)
• private StringBuffer st new
  StringBuffer10

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Mail Merge Application part 3

• private int readTemplate( ) throws Ioexception
  
• int n
• // Read the first portion of the template
• st0 readUpro(template, )
• // If there is there is an as the first
  char
• // read the rest of the template
• for (n 1 n lt 10 n)
• stn readUpto(template, )
• if (stn.length() 0) // might be
  empty
• return n
• return n

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Mail Merge Application part 4

• public void merge( ) throws Ioexception
• Stringbuffer sm
• in n readTemplate() // Read the first
  field
• sm readUpto(mailList, )
• while (true)
• // if no more fields
• if (sm.length() 0)return
• out.print(st0)
• // interleave template portions and fields
• for (int i 1 i lt n i)
• mailList.read( ) // get past new line
• out.print(sm) // print field
• out.print(sti) // print next
  template
• sm readUpto(mailList, )
• out.println(--------------------------------
  )

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Mail Merge Application part 5

• public void closeFiles( )
• out.close( )
• A typical client
• import java.io.
• public class MailMergeClient
• public static void main (String args)
• throws exception
  IOException
• MailMerge mm new MailMerge( )
• mm.openFiles(args0)
• mm.merge( )
• mm.closeFiles( )