CS 424524: Introduction to Java Programming

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CS 424/524 Introduction to Java Programming

• Lecture 10Spring 2004Department of Computer
  ScienceUniversity of AlabamaJoel Jones

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Java IO

• Efficiency achieved by introducing a simple
  buffer-oriented I/O model consisting of basic
  streams of bytes and characters together with
  monolithic, highly-tuned classes that combine
  support for buffering, formatting, and parsing.

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Topics

• java.io
• File
• FileIntputStream
• BufferedInputStream
• BufferedReader
• FileOutputStream
• BufferedOuputStream
• BufferedWriter
• IOException

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java.io package

• Interfaces
• Classes
• Exceptions

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This is the .05 Tour

• Java I/O By Elliotte Rusty Harold March 1999 
  1-56592-485-1, Order Number 4851594 pages,
  39.95 US 58.95 CA 28.50 UK

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Topics Revised

• How do I list a directory?
• How do I read data from a file?
• How do I write data to a file?
• How do I append data to a file?
• How do I format numbers like C's printf()?

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How do I list a directory?

• The File Class
• Misnomer the File class does not necessarily
  refer to a single file. It can represent the name
  of a single file, or the names of a set of files.
  
• The method list() returns a String array of
  file names

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Example

• try
• File path new File (.)
• String listing path.list()
• for(int count 0 count lt
• listing.length count)
• System.out.println(listcount)
• catch(Exception e)e.printStackTrace()

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How do I read data from a file?

• InputStream through inheritance, all derivatives
  of InputStream have the basic method read() to
  access a byte or an array of bytes
• FilterInputStream Class
• The FilterInputStream offers a grab bag of
  methods
• Sun this is the base class for enhancing input
  stream functionality
• Eckel we couldnt figure out where else to put
  this stuff, but it seemed like it belonged
  together TIJ (9th ed.)
• Avoid it--use InputStreamReader (JDK 1.1)

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Keyboard Access Use InputStreamReader
For reading keystrokes, use an InputStreamReader
Wrap with a BufferedReader decorator

• e.g.
• InputStreamReader iStreamReader new
  InputStreamReader(System.in)
• BufferedReader bReader new BufferedReader(iStrea
  mReader)

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File Access Use FileInputStream

• BufferedReader in new
• BufferedReader(new
• FileInputStream(
• fileName))

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BufferedReader in Action

• String strInput ""
• try
• strInput bReader.readLine()
• catch (Exception e)
• System.err.println(Input Error
• e.toString())

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Reading Numbers etc.

• You dont
• You read strings and convert the strings to
  numbers etc.
• e.g.
• inputString input.readLine()
• midterm1 Integer.parseInt(inputString)

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Constructors and Methods

• BufferedReader(Reader) Create a buffering
  character-input stream that uses a default-sized
  input buffer.
• BufferedReader(Reader, int) Create a buffering
  character-input stream that uses an input buffer
  of the specified size.
• close() Close the stream.
• mark(int) Mark the present position in the
  stream.
• markSupported() Tell whether this stream supports
  the mark() operation, which it does.
• read() Read a single character.
• read(char, int, int) Read characters into a
  portion of an array.
• readLine() Read a line of text.
• ready() Tell whether this stream is ready to be
  read.
• reset() Reset the stream to the most recent mark.
  
• skip(long) Skip characters.

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Choices DataInputStream

• Allows you to read primitive types
• No readLine() (deprecated)
• read(byte) Reads data into an array of bytes.
• readBoolean() Reads a boolean.
• readByte() Reads an 8 bit byte.
• readChar() Reads a 16 bit char.
• readDouble() Reads a 64 bit double.
• readFloat() Reads a 32 bit float.
• readInt() Reads a 32 bit int.
• readLine() Reads in a line that has been
  terminated by a \n, \r, \r\n or EOF. Deprecated.
• readLong() Reads a 64 bit long.
• readShort() Reads a 16 bit short.

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How do I write data to a file?

• FileOutputStream decorated with a PrintWriter
• e.g.
• FileOutputStream fout new
• FileOutputStream("test.out")
• PrintWriter myOutput new
• PrintWriter(fout)
• myOutput.println("Hello There!")

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Dont forget try blocks!

• IOException
• try
• //open file(s)
• catch (IOException e)
• System.out.println(
• "Error opening file " e)
• System.exit(1)

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How do I append data to a file?

• just pass true as the second argument to this
  FileOutputStream constructor to indicate that you
  want to append data to the file
• public FileOutputStream(String name, boolean
  append)

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How do I format numbers like C's printf()?

• You dont. You build a string and print the
  string.
• the java.text package contains classes that
  format numbers according to particular needs. In
  particular it's worth getting to know the
  java.text.NumberFormat and java.text.DecimalFormat
  classes

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Efficiency BufferedWriter

• Wrap a BufferedWriter around FileWriters
• Example
• PrintWriter out
• new PrintWriter(
• new BufferedWriter(
• new FileWriter("foo.out")))

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Where to Get More Information

• http//java.sun.com/products/jdk/1.2/docs/api/java
  /io/package-summary.html