io and serialization

IADCS Diploma CourseInput/Output and Serialization

U Nyein Oo

COO/Director(IT)

Myanma Computer Co., Ltd

Copyright: MCC Input/Output and Serialization 2

How the Java Platform Supports I/O

The package java.io supports console I/O and file I/O Console I/O is character keyboard input and output

without the mouse graphics of a graphical user interface File I/O involves reading and writing data to and from a

mass storage device, typically the computer’s hard drive The new I/O (NIO) package java.nio supplements the

original I/O package


Programming I/O

In stream I/O, characters or bytes are read or written sequentially

The Java platform includes two dual hierarchies of classes that support streams:

– byte-oriented input and output – character-oriented input and output

The class RandomAccessFile is used to read and write arbitrary locations within a file without first having to read or write all the bytes or characters that precede that location


Byte-Oriented Stream Classes


Predefined Stream Objects

All Java programs can use three stream objects that are defined in the System class of the java.lang package:

– System.in The field System.in is a java.io.BufferedInputStream object

– System.out The field System.out is a java.io.PrintStream object

– System.err The field System.err is a java.io.PrintStream object


Input Methods

Input methods of the java.io.InputStream class:– int available()– void close()– void mark( int readlimit)– boolean markSupported()– int read()– int read(byte[] buffer)– int read( byte[] buffer, int offset, int length) – void reset()– long skip(long bytecount)


Output Methods

Output methods of the java.io.OutputStream class:– void close()– void flush()– void write( int b)– void write(byte[] buffer)– void write( byte[] buffer, int offset, int length)


Other Byte I/O Classes

Extensions of InputStream include the following classes:• The class ByteArrayInputStream lets you read an array of bytes

as though it were an InputStream object• The class SequenceInputStream provides a mechanism for

concatenating the data from two or more InputStream objects into a single, seamless stream

• The class PipedInputStream implements half of a pipe to connect the input stream of one thread or process to the output stream of another thread process


Other Byte I/O Classes

Extensions of OutputStream include the following classes:

– The class ByteArrayOutputStream sends its output into an object of type byte

– The class PipedOutputStream is the complementary class to PipedInputStream


Parsing an Input Stream

The next step after reading a line of input is to parse it, or break it into separate tokens

A token usually consists of a sequence of characters that does not include a space, newline, tab, or other nonprinting character

To tokenize a string, you can use the StringTokenizer class provided by the java.util package


Random-Access File I/O

The class RandomAccessFile supports byte-oriented I/O to and from random-access files

The class RandomAccessFile extends Object RandomAccessFile combines input and output operations

in one class The seek method selects the position within the file where

the next I/O operation will begin


Character Streams


Connecting Byte & Character I/O Classes

The Java platform includes adapter classes that bridge between character I/O classes and byte I/O classes:– InputStreamReader– OutputStreamWriter


Using Other Character I/O Classes

Extensions of the Reader object include the following:– The class CharArrayReader lets you read an array of

characters as though it were a Reader object– The class StringReader lets you read a String object as

though it were a Reader object– The class PipedReader implements half of a pipe and is

especially useful for communication between threads.


Using Other Character I/O Classes

Extensions of the Writer object include the following:– The class CharArrayWriter sends its output into an object of

type char[]– The class StringWriter lets you write to a StringBuffer object

as though it were a Writer object– The class PipedWriter is the complementary class to

PipedReader– The class PrintWriter is the character I/O equivalent of the

PrintStream class


The New I/O (NIO) Interface

The java.nio package provides new features:

– Support for buffer management– A new primitive I/O abstraction called a channel– File locking at the process level

– Memory mapping


Buffers

Capacity: the maximum number of data elements that the buffer can contain

Limit: a reflection of the amount of data that the buffer currently contains and is defined as the index of the first element in the buffer that should not be read or written

Mark: the index to which the position value will be set if the buffer is reset

Position: the index of the next element to be read or written and can never exceed the limit


Buffer Classes in java.nio


Object Serialization

Object serialization: a general solution that lets you write objects to I/O streams and then read them, without defining any additional methods

Enables transmission of objects over a network or save objects to files between runs of your program

The object serialization feature is an important component of the Java Remote Method Invocation (RMI) enterprise API


Using Object Streams

Two stream classes support object serialization: – ObjectOutputStream - a subclass of OutputStream– ObjectInputStream - a subclass of InputStream

To create an ObjectOutputStream object, provide an existing OutputStream object as the argument of the constructor

To create an ObjectInputStream object, provide an existing InputStream object as the argument of the constructor


Suppressing Serialization of Fields

Include the qualifier transient when you declare fields to indicate that they should not be serialized with instances of the class

Fields that have the transient qualifier are not output when the object is serialized

When the object is deserialized later, transient fields are given the default value normally used for fields of their type

io and serialization

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