Cup 8: File Input and Output

1
Cup 8 File Input and Output

• Special Topics Java

Dr. Tim Margush Department of Mathematics and
Computer Science The University of Akron
2
Streams

• Character Stream
• A sequence of Unicode characters
• Unicode is automatically converted to and from
  the local host representation
• Byte Stream
• A sequence of Byte values
• No translation
• Binary mode

3
java.io Classes

• File
• A file or directory
• OutputStream, InputStream
• Base class for Byte streams
• Writer, Reader
• Base class for Character streams
• RandomAccessFile

4
The File Class

• Constructors
• File(String fileOrPathName)
• File(File directory, String fileName)
• File(String directory, String fileName)
• Once a File object is created, information may be
  obtained from the various methods

5
Selected File Methods

• Boolean functions
• exists()
• isDirectory()
• isFile()
• canRead()
• canWrite()
• equals(File)

• String getName()
• String getPath()
• String list()
• returns an array of filenames if the object
  represents a directory
• long length()
• number of bytes in the file

6
File Modifications

• delete()
• deletes the file represented by the current File
  object
• renameTo(FilePath)
• renames and possibly moves the file named by the
  current object
• mkdir() and mkdirs()
• creates a directory (perhaps a whole path) named
  by the current object

7
OutputStream Methods

• write(int b)
• write(byte b)
• write(byte b, int offset, int length)
• flush()
• close()
• These methods define functionality - they are
  generally overridden in subclasses

8
OutputStream Derivations

• FileOutputStream
• stream is directed to a file
• ByteArrayOutputStream
• stream is directed to a byte array
• PipedOutputStream
• stream is intended to connect to a
  PipedInputStream
• FilterOutputStream
• a base class for further capabilities

9
Data and Buffered OutputStream Classes

• Derived from FilterOutputStream
• DataOutputStream
• used to write primitive data in binary mode - no
  translation
• BufferedOutputStream
• adds buffering to improve performance
• Constructors require an object of one of the
  other OutputStream types

10
DataOutputStream

• Used when writing data that is not strictly
  character data
• creates a sequence of bytes corresponding to the
  internal representation of data
• methods exist to write all of the primitive types
  as well as a String
• results are usually not human readable

11
Character Output Streams

• StringWriter
• CharArrayWriter
• PipedWriter
• OutputStreamWriter
• PrintWriter
• provides String output for other Writers
• BufferedWriter
• buffers other Writers
• FilterWriter

• None of these are directly related to a file
• FileWriter
• derived from OutputStreamWriter
• writes data to a File named in the constructor

12
PrintWriter

• Constructed from a Writer or an OutputStream
  object
• Used to output formatted representa-tions of
  objects to a text stream
• Includes print() and println() methods
• these are overloaded for all of the basic types
  and will output any object using its toString
  method

13
Formatting Output

• java.text contains numerous classes dealing with
  text - data conversions
• Support is provided for internationalization via
  getLocale()
• After creating a format object, it may be used to
  format data (convert to String representations)

14
Input Streams

• A collection of classes parallel the Output
  stream classes, beginning with InputStream at the
  top of the hierarchy

• FileInputStream
• SequenceInputStream
• PipedInputStream
• ByteArrayInputStream
• FilterInputStream
• ObjectInputStream

15
FilterInputStream

• DataInputStream
• support for basic data types (binary)
• BufferedInputStream
• add buffering to existing stream
• LineNumberInputStream
• count lines of input

• PushBackInputStream
• allow bytes to be placed back into the stream for
  rereading
• plus Additional classes providing support for
  data decompression and security

16
Character Input Streams

• Derived from Reader
• Provides automatic characer code conversion from
  native encoding method

• StringReader
• CharArrayReader
• PipedReader
• InputStreamReader
• FileReader
• BufferedReader
• LineNumberReader
• FilterReader
• PushBackReader

17
Formatted Input

• java.io.StreamTokenizer
• used to split character data into meaningful
  tokens that can be parsed by other methods
• method nextToken() parses the next token of the
  Stream and places its value in a public instance
  variable
• double nval or String sval
• TT_NUMBER, TT_WORD, TT_EOF, TT_EOL

18
StringTokenizer

• java.util.StringTokenizer
• nextToken() method returns a substring with no
  whitespace
• BufferedReader contains readLine() method
• Conversion
• Integer.parseInt(x) //decimal
• Integer.parseInt(x,16) //hex input
• etc

19
Object I/O - Serialization

• ObjectOutputStream
• created from a DataOutputStream
• contains writeObject() method
• Object must implement the Serializable Interface

• ObjectInputStream
• created from a DataInputStream
• contains readObject() method
• Object must be Serializable

20
implements Serializable

• This one is eay - there are no special methods
  that you are required to implement!
• A default constructor must exist
• All the data members must be a basic data type,
  or an object that is itself Serializable
• Members to be omitted from the object stream are
  declared transient