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SCJP: Basic Java I/O #Java Short Notes #SCJP

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  • ByteStream is the basic I/O stream. Handles data as a stream of bytes. Does operation with byte unit and uses 8 bit. FileInputStream, FileOutputStream - can be used to copy files as byte by byte.
  • Character Streams: FileReader and FileWriter are character streams. They treat file data as 16 bit unicode charater streams.
  • InputStreamReader, OutputStreamWriter are also character streams. May be used in socket data reading.
  • Line-Oriented I/O: BufferedReader and PrintWriter
  • Buffered Streams: BufferedInputStream and BufferedOutputStream create buffered byte streams, while BufferedReader and BufferedWriter create buffered character streams
  • You can set autoflush() of buffered streams or call manually flush() method.
  • The scanner API breaks input into individual tokens. The formatting API assembles data into nicely formatted, human-readable form.
  • Scanner: 
    Scanner scanner = new Scanner(new BufferedReader(new FileReader("test.txt")));            while (s.hasNext()) {                System.out.println(s.next());            }
  • To create formatted output streams, instantiate PrintWriter not PrintStream
  • Check: System.out.format("The square root of %d is %f.%n", i, r);
  • System.out and System.err are PrintStream objects. PrintStream is really a byte stream but uses some mechanism to emulate character stream.
  • InputStreamReader cin = new InputStreamReader(System.in); System.in is a byte stream. InputStreamReader is used to emulate a character stream.
  • System.console provides character streams to handle console read/write operations. Provides readPassword method to read password from the console
  • Data Streams: Support I/O operations of primitive data types. DataInputStream and DataOutputStream.
  • Check: 
    out = new DataOutputStream(new            BufferedOutputStream(new FileOutputStream(dataFile)));out.writeDouble(prices);out.writeInt(units);out.writeUTF(descs);
  • DataStreams detects an end-of-file condition by catching EOFException
  • Correct type to represent currency values: java.math.BigDecimal - an object type
  • Object Streams: ObjectInputStream and ObjectOutputStream. Use writeObject and readObject to write and read objects respectively.
  • A stream can contain only one copy of an object but many references to it when required.
  • File Objects: File I/O
  • Random access file: 
    new RandomAccessFile("test.txt", "r");new RandomAccessFile("test.txt", "rw");RandomAccessFile methods:    * int skipBytes(int)     * void seek(long)      * long getFilePointer()
  • The new java.nio.* package provides supports to handle file i/o for high performance applications.

From: http://sitestree.com/?p=4878
Categories:Java Short Notes, SCJP
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Post Data:2012-10-24 02:25:07

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