Java IO Stream
Java performs I/O through Streams. A Stream is a continuous flow of data.
Streams are clean way to deal with input/output. Java encapsulates Stream
under java.io package. Java defines two types of streams. They are,
1. Byte Stream : It provides a convenient means for handling input and output of byte.
2. Character Stream : It provides a convenient means for handling input and output of
characters. Character stream uses Unicode and therefore can be internationalized.
Java Byte Stream Classes
Byte stream is defined by using two abstract class at the top of hierarchy, they are
InputStream and OutputStream.
These two abstract classes have several concrete classes that handle various devices such as disk files, network connection etc.
|
Some important Byte
stream classes |
Stream class
Description |
|
BufferedInputStream |
Used for Buffered Input
Stream. |
|
BufferedOutputStream |
Used for Buffered Output
Stream. |
|
DataInputStream |
Contains method for
reading java standard datatype |
|
DataOutputStream |
An output stream that
contain method for writing java standard data type |
|
FileInputStream |
Input stream that reads
from a file |
|
FileOutputStream |
Output stream that write
to a file. |
|
InputStream |
Abstract class that
describe stream input. |
|
OutputStream |
Abstract class that
describe stream output. |
|
PrintStream |
Output Stream that contain
print() and println() method |
These classes define several key methods. Two most important are
1. read() : reads byte of data.
2. write() : Writes byte of data.
Java Character Stream Classes
Character stream is also defined by using two abstract class at the top of hierarchy,they are Reader and Writer.
These two abstract classes have several concrete classes that handle unicode character.
|
Some important Byte
stream classes |
Stream class
Description |
|
BufferedReader |
Handles buffered input stream. |
|
BufferedWriter |
Handles buffered output stream. |
|
FileReader |
Input stream that reads from file. |
|
FileWriter |
Output stream that writes to file. |
|
InputStreamReader |
Input stream that translate byte to
character |
|
OutputStreamReader |
Output stream that translate character to
byte. |
|
PrintWriter |
Output Stream that contain print() and
println() method. |
|
Reader |
Abstract class that
define character stream input |
|
Writer |
Abstract class that define character stream
output |
Reading Console Input
We use the object of BufferedReader class to take inputs from the keyboard.
BufferedReader br=new BufferedReader(InputStreamReader(System.in))
br ==> object of BufferedReader
Input StreamReader ==> sub class of Reader, converts byte into character
System.in ==> used to read Console inputs
Reading Characters
read() method is used with BufferedReader object to read characters. As this function returns integer type value has we need to use typecasting to convert it into char type.
int read() throws IOException
Below is a simple example explaining character input.
class CharRead
{
public static void main( String args[])
{
BufferedReader br = new Bufferedreader(new
InputstreamReader(System.in));
char c = (char)br.read(); //Reading character
}
Reading Strings in Java
To read string we have to use readLine() function with BufferedReader class's object.
String readLine() throws IOException
Program to take String input from Keyboard in Java
import java.io.*;
class MyInput
{
public static void main(String[] args)
{
String text;
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
text = br.readLine(); //Reading String
System.out.println(text);
}
}
Program to read from a file using BufferedReader class
import java. Io *;
class ReadTest
{
public static void main(String[] args)
{
try
{
File fl = new File("d:/myfile.txt");
BufferedReader br = new BufferedReader(new FileReader(fl)) ;
String str;
while ((str=br.readLine())!=null)
{
System.out.println(str);
}
br.close();
fl.close();
}
catch(IOException e) {
e.printStackTrace();
}
}
}
Program to write to a File using FileWriter class
import java. Io *;
class WriteTest
{
public static void main(String[] args)
{
try
{
File fl = new File("d:/myfile.txt");
String str="Write this string to my file";
FileWriter fw = new FileWriter(fl) ;
fw.write(str);
fw.close();
fl.close();
}
catch (IOException e)
{ e.printStackTrace(); }
}
}
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