Input Output Streams.ppt standard input output

Input Output Streams.ppt standard input output

• 1.
  Standard input, outputand error
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  Lecture Under Construction
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  Contents • Overview ofI/O Streams • Character Streams • Byte Streams • Using the Streams • Object Serialization • Working with Random Access files • Standard IO Streams
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  Overview of I/OStreams To bring in information, a program opens a stream on an information source (a file, memory, a socket) and reads the information sequentially, as shown in the following figure.
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  Similarly, a programcan send information to an external destination by opening a stream to a destination and writing the information out sequentially, as shown in the following figure. Overview of I/O STREAMS Contd.
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  Overview of I/Ostreams Contd.. • The java.io package contains a collection of stream classes that support algorithms for reading and writing. To use these classes, a program needs to import the java.io package. • The stream classes are divided into two class hierarchies, based on the data type (either characters or bytes) on which they operate i.e Character Stream and Byte Stream
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  Character Streams • Readerand Writer are the abstract superclasses for character streams in java.io. • Reader provides the API and partial implementation for readers ( streams that read 16-bit characters ) and Writer provides the API and partial implementation for writers ( streams that write 16-bit characters).
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  Character Streams Contd. •The following figure shows the class hierarchies for the Reader and Writer classes.
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  Byte Streams • Toread and write 8-bit bytes, programs should use the byte streams, descendents of InputStream and OutputStream . • InputStream and OutputStream provide the API and partial implementation for input streams (streams that read 8-bit bytes) and output streams (streams that write 8-bit bytes).
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  Byte Streams (cont.) •These streams are typically used to read and write binary data such as images and sounds. • Two of the byte stream classes, ObjectInputStream and ObjectOutputStream, are used for object serialization.
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  Byte Streams (cont.) •The class hierarchy for the Reader Class
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  Byte Stream (cont.) •Class hierarchy figure for Writer Class
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  How to UseFile Streams The file streams-- FileReader , FileWriter , FileInputStream , and FileOutputStream -- read or write from a file on the native file system. Here is simple code to create a file reader File inputFile = new File("farrago.txt"); FileReader in = new FileReader(inputFile); FileWriter out = new FileWriter(outputFile); This reads characters from the reader as long as there's more input in the input file and writes those characters to the writer.
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  How to UsePipe Streams • Pipes are used to channel the output from one thread into the input of another. PipedReader and PipedWriter (and their input and output stream counterparts PipedInputStream and PipedOutputStream ) implement the input and output components of a pipe.
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  How to wrapa stream Streams are wrapped to combine the various features of the many streams. example code: BufferedReader in = new BufferedReader(source); The code opens a BufferedReader on source, which is another reader of a different type. This essentially "wraps" source in a BufferedReader. The program reads from the BufferedReader, which in turn reads from source.
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  How to ConcatenateFiles • The SequenceInputStream creates a single input stream from multiple input sources. example code : ListOfFiles mylist = new ListOfFiles(args); SequenceInputStream s = new SequenceInputStream(mylist); Here, the mylist object is an enumeration that SequenceInputStream uses to get a new InputStream whenever it needs one.
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  Working with FilterStreams • The java.io package provides a set of abstract classes that define and partially implement filter streams. A filter stream filters data as it's being read from or written to the stream. • The filter streams are FilterInputStream , and FilterOutputStream . • A filter stream is constructed on another stream (the underlying stream).
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  Object Serialization • Twostream classes in java.io, ObjectInputStream and ObjectOutputStream, are used to read and write objects. • The key to writing an object is to represent its state in a serialized form sufficient to reconstruct the object as it is read. This process is called object serialization.
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  Uses of ObjectSerialization • Remote Method Invocation (RMI)-- communication between objects via sockets • Lightweight persistence--the archival of an object for use in a later invocation of the same program.
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  Working with RandomAccess Files • A random access file permits non-sequential or random access to a file's contents. • Using Random Access Files Unlike the input and output stream classes in java.io, RandomAccessFile is used for both reading and writing files. You create a RandomAccessFile object with different arguments depending on whether you intend to read or write.
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  Standard IO Streams •There are three standard streams, all of which are managed by the java.lang.System class • Standard input--referenced by System.in – Used for program input, typically reads input entered by the user. • Standard output--referenced by System.out – Used for program output, typically displays information to the user. • Standard error--referenced by System.err – Used to display error messages to the user.
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  References • http://java.sun.com/docs/books/tutorial/ essential/TOC.html#io • http://www.codeguru.com/java/tij/ tij0114.shtml