අද මං කියල දෙන්න යන්නේ
ජව වල තියන තවත් concept එකක් වෙන Input and Output Streams ගැන.මේවා යොදාගන්නේ ප්‍රදාන
වශයෙන්ම යම් තොරුතුරු මුලාශරයක් සමග සන්නීවේදනය කරන්න.මේ දත්ත මුලාශ්‍රය file
,computer memory හෝ අන්තර්ජාලය වෙන්න පලුවන්.
Input Streams :-දත්ත මුලාශ්‍රයකින්
දත්ත කියවීම.
Output Streams :- දත්ත මුලශ්‍රයකට දත
ලිවීම.
ජාවා වල ප්‍රදාන වශයෙන්
ස්ට්‍රීම්ස් දෙකක් තියනවා
1)Byte Streams :-
මේවා use කරන්නේ Bytes
වල Input හා Output Handel කරන්න.
2)
Charactor Streams :- මේවා use කරන්නේ Charactors වල Input හා Output Handel කරන්න.
Byte Stream Classes
මුලින්ම කියන්න ඕනේ මේවට අවශ ගොඩක් class ජව වල කලින් define කරලා තියනවා.අපිට අපි එක use කරලා ඒවා බලාගන්න පලුවන්.මේවා inherit වෙන මූලිකම class දෙක තමයි InputStream
හා OutputStream කියන්නේ.
Character Stream Classes
අපි යොදාගන්න ගොඩක් character stream class තියන්නේ ජාවා වල IO කියන paccage එකේ .එකට ගියෝත්හ් API එකේ ඔයාලට පහසුවෙන් බලාගන්න පලුවන් ඒ
class මොනවද කියල.
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Java™ Platform
Standard Ed. 6 |
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Package java.io
Provides for
system input and output through data streams, serialization and the file
system.
Class
Summary
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A BufferedInputStream adds functionality to another
input stream-namely, the ability to buffer the input and to support the mark and reset methods.
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The class
implements a buffered output stream.
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Reads text
from a character-input stream, buffering characters so as to provide for the
efficient reading of characters, arrays, and lines.
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Writes
text to a character-output stream, buffering characters so as to provide for
the efficient writing of single characters, arrays, and strings.
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A ByteArrayInputStream contains an internal buffer that
contains bytes that may be read from the stream.
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This class
implements an output stream in which the data is written into a byte array.
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This class
implements a character buffer that can be used as a character-input stream.
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This class
implements a character buffer that can be used as an Writer.
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Methods to
access the character-based console device, if any, associated with the
current Java virtual machine.
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A data
input stream lets an application read primitive Java data types from an
underlying input stream in a machine-independent way.
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A data
output stream lets an application write primitive Java data types to an
output stream in a portable way.
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An
abstract representation of file and directory pathnames.
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Instances
of the file descriptor class serve as an opaque handle to the underlying
machine-specific structure representing an open file, an open socket, or
another source or sink of bytes.
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A FileInputStream obtains input bytes from a file
in a file system.
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A file
output stream is an output stream for writing data to a File or to a FileDescriptor.
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This class
represents access to a file or directory.
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Convenience
class for reading character files.
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Convenience
class for writing character files.
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A FilterInputStream contains some other input stream,
which it uses as its basic source of data, possibly transforming the data
along the way or providing additional functionality.
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This class
is the superclass of all classes that filter output streams.
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Abstract
class for reading filtered character streams.
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Abstract
class for writing filtered character streams.
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This
abstract class is the superclass of all classes representing an input stream
of bytes.
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An
InputStreamReader is a bridge from byte streams to character streams: It
reads bytes and decodes them into characters using a specified charset.
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Deprecated. This class incorrectly
assumes that bytes adequately represent characters.
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A buffered
character-input stream that keeps track of line numbers.
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An
ObjectInputStream deserializes primitive data and objects previously written
using an ObjectOutputStream.
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Provide
access to the persistent fields read from the input stream.
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An
ObjectOutputStream writes primitive data types and graphs of Java objects to
an OutputStream.
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Provide
programmatic access to the persistent fields to be written to ObjectOutput.
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Serialization's
descriptor for classes.
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A description
of a Serializable field from a Serializable class.
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This
abstract class is the superclass of all classes representing an output stream
of bytes.
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An
OutputStreamWriter is a bridge from character streams to byte streams:
Characters written to it are encoded into bytes using a specified charset.
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A piped
input stream should be connected to a piped output stream; the piped input
stream then provides whatever data bytes are written to the piped output
stream.
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A piped
output stream can be connected to a piped input stream to create a
communications pipe.
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Piped
character-input streams.
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Piped
character-output streams.
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A PrintStream adds functionality to another
output stream, namely the ability to print representations of various data
values conveniently.
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Prints
formatted representations of objects to a text-output stream.
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A PushbackInputStream adds functionality to another
input stream, namely the ability to "push back" or
"unread" one byte.
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A
character-stream reader that allows characters to be pushed back into the
stream.
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Instances
of this class support both reading and writing to a random access file.
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Abstract
class for reading character streams.
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A SequenceInputStream represents the logical
concatenation of other input streams.
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This class
is for Serializable permissions.
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The StreamTokenizer class takes an input stream and
parses it into "tokens", allowing the tokens to be read one at a
time.
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Deprecated. This class does not
properly convert characters into bytes.
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A
character stream whose source is a string.
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A
character stream that collects its output in a string buffer, which can then
be used to construct a string.
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Abstract
class for writing to character streams.
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Exception
Summary
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Base class
for character conversion exceptions.
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Signals
that an end of file or end of stream has been reached unexpectedly during
input.
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Signals
that an attempt to open the file denoted by a specified pathname has failed.
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Signals
that an I/O operation has been interrupted.
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Thrown
when the Serialization runtime detects one of the following problems with a
Class.
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Indicates
that one or more deserialized objects failed validation tests.
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Signals
that an I/O exception of some sort has occurred.
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Thrown
when serialization or deserialization is not active.
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Thrown
when an instance is required to have a Serializable interface.
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Superclass
of all exceptions specific to Object Stream classes.
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Exception
indicating the failure of an object read operation due to unread primitive
data, or the end of data belonging to a serialized object in the stream.
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Thrown
when control information that was read from an object stream violates
internal consistency checks.
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Signals
that a sync operation has failed.
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The
Character Encoding is not supported.
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Signals
that a malformed string in modified UTF-8 format has been read in a data
input stream or by any class that implements the data input interface.
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Signals
that one of the ObjectStreamExceptions was thrown during a write operation.
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අපි මේ ඔක්කොම class මතක
තියාගන්න ඕනේ නෑ.අවශ වෙලාවට API එක use කරලා ඒවා පාවිචි කරන්නේ කොහොමද කියල විතරයි
දැනගන්න ඕනේ.දැන් අපි බලමු මේවා use කරන විදිය.
Console Input
මුලික වශයෙන්ම System කියන එකට free define stream veriable තුනක්
තියනවා.in ,out,err යන ඒවා.අපි පොඩ්ඩක් පහත programme එක පොඩ්ඩක් බලමු.
import java.util.Scanner;
public class Demo {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc=new Scanner(System.in);//Create
Scanner object
String fileName;
sc.next();
sc.nextLine();
sc.nextInt();
}
}
මේකෙදි කරන්නේ Scannner object එකක් හදල එකේ තියන කිලින් define කරපු method පාවිචි
කරලා විවිද consol input ගන්න එක තමයි.අපිට API එකින් පලුවන් මේකට අදාල ඔක්කොම method බලාගන්න. http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html මේ
තියන්නේ Scanner
class එකේ online API ලින්ක් එක.
Console Output
Console Output එක ගන්න අපි සාමාන්යෙන් use කරන්නේ print() සහ
println() කියන method දෙක තමයි.නමුත් Console Output ගන්න recommended method එක තමයි PrintWriter stream එක use කරන එක. අපි දැන් බලමු PrintWriter stream එක use කරන විදිය ...
import java.io.PrintWriter;
public class Demo {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
PrintWriter pw = new PrintWriter(System.out, true);
pw.println("This is a string");
int i = -7;
pw.println(i);
double d = 4.5e-7;
pw.println(d);
}
}
අපි තව programme එකක් බලමු.
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Date;
public class Demo {
/**
* @param args
*/
public static void main(String[] args) {
PrintWriter pwFile = null;
int i=0;
Date date = new Date();
try{
pwFile = new PrintWriter("FileName");
i++;
pwFile.println(date);
pwFile.write("Write something in a line. i = "+i);
System.out.println("Write
to the file successfully");
}catch(FileNotFoundException e) {
e.printStackTrace();
}catch(SecurityException e) {
e.printStackTrace();
}finally {
if(pwFile != null){
pwFile.close();
}
}
}
}
මේ programme එකේ කරන්නේ printWriter එකට දෙන Destination file එකට
දවස print කරන එක තමයි.
Object Serialization
ජාවා වලින් සපයන Object Serialization කියන technique එක use කරලා byte sequence එකක් විදියට object එකක තියන data
,information වගේ දේවල් නීරුපනය කරන
එක තමයි.
Serialization සාමාන්යෙන් use කරන්නේ graphs , trees වගේ සංකීර්ණ data structures වල තමයි.
අපි දැන් මේකට පොඩි උදාහරණ ටිකක් බලමු.
import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
public class Demo {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
MyClass object1 = new MyClass("Hello", -7);
System.out.println("object1:
" + object1);
FileOutputStream fos = new FileOutputStream("serial");
ObjectOutputStream oos =
new
ObjectOutputStream(fos);
oos.writeObject(object1);
oos.flush();
oos.close();
}
catch(Exception e) {
System.out.println("Exception
during serialization: " + e);
System.exit(0);
}
}
}
class MyClass{
String st;
float ft;
public MyClass(String st,float ft) {
// TODO Auto-generated constructor stub
this.st=st;
this.ft=ft;
}
}
මේ ගැන තව උදාහරණ පහත
ලින්ක් වලින් බලාගන්න පලුවන්.
අපි දැන් බලමු file operation ටිකක් කරන්න පොඩි programme කිහිපයක්.
import java.io.File;
public class file1 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
File f=new File("Path");
if(f.isDirectory()){
System.out.println("Given
file is:"+f.isDirectory());
}
}
}
මේ programme එකින්
කරන්නේ file එකක් load කරලා එක Directory එකක්ද කියල
බලනවා.path කියන තැනට file එක තියන තැන හරියටම path එක දෙන්න ඕනේ.අපිට file class
එකේ තියන methodes , isDirectory() වගේ use කරලා විවිද වැඩ කරගන්න
පලුවන්.ඔයගොල්ලොන්ට අනිත් method ඕනනම් API එක use කරලා බලන්න.
දැන් අපි තව
උදාහරණයක් බලමු.
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class file1 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
BufferedReader buffer=new BufferedReader(new FileReader("file
Path"));
buffer.read();
buffer.readLine();
buffer.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
මේ programme එකේ BufferReader එකක් use කරලා තමයි file එක buffer කරගන්නෙ.එටපස්සේ පලුවන් method use කරලා විවිද වැඩ ගන්න පලුවන්.
මේවගේ අනිත් IO class use කරන්න පලුවන්.මං හිතන්නේ මේ පොස්ට් එකින් ඔයාලට Input and
Output Streams ගැන පොඩි දැනුමක් එන්න
ඇති කියල.නැවත අලුත් පොස්ට් එකකින් හමුවෙමු....
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