Lecture 02 Object Oriented Programming

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Lecture 13Streams
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Introduction

• Users use the term file to describe the objects
  that they stores on permanent storage devices
• Data files contain facts and figures
• Program files store software instruction
• Store information from one execution of a project
  until the next execution
• Use an object, store it, and then recreate the
  object exactly as it existed at a later time
• Use the File class to gather information
• Obtain information about file, such as whether it
  exists or is open, its size, and its last
  modification date, etc.

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Introduction

• Include the statement java.io.
• Input and output contains all the classes used in
  file processing
• Creating a file object
• File someData new File (data.txt)
• File someData new File (C\\temp\\data.txt)

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File Class Methods

• boolean canRead( )
• Returns true if a file is readable
• boolean canWrite( )
• Return true if a file is writeable
• boolean exists( )
• Return true if a file exists
• String getName( )
• Return the files name
• String getPath( )
• Return the files path
• long length( )
• Returns the files size
• long lastModified( )
• Return the time the file was last modified. This
  time is system-dependent
• Example 01 and Example 02

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Data File

• Character
• Any one of the letters
• Field
• A group of characters
• Records
• A group of field
• File
• A group of record

Employee file
Andrews record
Brown record
ID 786
Brown
Jennifer
B
r
o
w
n
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Data File

• Before a program can use a file, the program must
  open the file and close the file when the program
  is finished.
• When you leave a file open for no reason,
  computer resources will be suffered
• In Java, when you perform an input operation in a
  program, you can picture bytes flowing into your
  program fro an input devices through a stream,
  and when you perform output, some bytes flow out
  of your program through another stream to an
  output devices

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Streams

• The most basic of input/output with Java is done
  with stream
• The stream can flow from the program to the
  screen, from a keyboard to the program, to/from a
  disk file or other storage media, to a printer,
  or even to a network or the Web
• The stream commands enable you to write to a disk
  file or to the output screen

Java program
Input stream
Output stream
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Streams
Object
OutputStream
RandomAccessFile
InputStream
FileOutputStream
FilterOutputStream
FileInputStream
FilterInputStream
DataInputStream
BufferedInputStream
BufferedOutputStream
PrintStream
DataOutputStream
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Streams

• FileInputStream and OutputStream provide the
  capability to read from and to write to disk
  files
• Create your own InputStream and OutputStream
  objects
• assign System.in and System.out
• Example Read from KB

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Output to the Screen

• Send an output stream to the standard output
  device
• Read an input stream from the standard input
  device
• Java has three standard IO objects in, out, and
  err
• System.out.println(Welcome)

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Writing to a File

• Assign a file to the InputStream or OutputStream
• Read data from the keyboard and store it
  permanently on a disk
• Construct a FileOutputStream object and assign it
  to the OutputStream
• Create a File object passing the filename to the
  File constructor. Then pass the File object to
  the constructor of the FileOutputStream class
• Example Write file
• Example Read file

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Writing a Formatted File Data

• Rather than reading a series of bytes, it is more
  useful to be able to read such a file in groups
  of bytes that constitute an integer, a String,
  and a double.
• DataOutputStream objects enable us to write
  binary data to an OutputStream
• The data with DataOutputStream objects is not
  readable in a text editor
• Can read the data with a DataInputStream object
• Methods
• writeBoolean( ), writeChar ( ), writeDouble( ),
  writeFloat( ), writeInt( ), writeUTF()

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Writing a Formatted File Data

• Define a DataOutputStream object
• DataOutputStream out
• When you call the DataOutputStream constructor,
  pass a FileOutputStream object
• out new DataOutputStream ( new FileOutputStream
  (someFile))
• Example

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Reading Formatted File Data

• DataInputStream objects enable us to read binary
  data form an InputStream
• readByte(), readChar(), readDouble(),
  readFloat(), readInt(), and readUTF()
• DataInputStream in
• In new DataInputStream(FileInputStream
  (somefile))
• Example