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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
Copyright: MCC Input/Output and Serialization 3
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
Copyright: MCC Input/Output and Serialization 4
Byte-Oriented Stream Classes
Copyright: MCC Input/Output and Serialization 5
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
Copyright: MCC Input/Output and Serialization 6
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)
Copyright: MCC Input/Output and Serialization 7
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)
Copyright: MCC Input/Output and Serialization 8
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
Copyright: MCC Input/Output and Serialization 9
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
Copyright: MCC Input/Output and Serialization 10
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
Copyright: MCC Input/Output and Serialization 11
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
Copyright: MCC Input/Output and Serialization 12
Character Streams
Copyright: MCC Input/Output and Serialization 13
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
Copyright: MCC Input/Output and Serialization 14
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.
Copyright: MCC Input/Output and Serialization 15
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
Copyright: MCC Input/Output and Serialization 16
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
Copyright: MCC Input/Output and Serialization 17
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
Copyright: MCC Input/Output and Serialization 18
Buffer Classes in java.nio
Copyright: MCC Input/Output and Serialization 19
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
Copyright: MCC Input/Output and Serialization 20
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
Copyright: MCC Input/Output and Serialization 21
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