IO Stream

Java performs I/O through Streams. A Stream is linked to a physical layer by java I/O system to make input and output operation in java. In general, a stream means continuous flow of data. Streams are clean way to deal with input/output without having every part of your code understand the physical.

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.

Byte Stream Classes

Byte stream is defined by using two abstract class at the top of hierarchy, they are InputStream and OutputStream.

byte stream classification

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 classDescription
BufferedInputStreamUsed for Buffered Input Stream.
BufferedOutputStreamUsed for Buffered Output Stream.
DataInputStreamContains method for reading java standard datatype
DataOutputStreamAn output stream that contain method for writing java standard data type
FileInputStreamInput stream that reads from a file
FileOutputStreamOutput stream that write to a file.
InputStreamAbstract class that describe stream input.
OutputStreamAbstract class that describe stream output.
PrintStreamOutput 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.


Character Stream Classes

Character stream is also defined by using two abstract class at the top of hierarchy, they are Reader and Writer.

character stream classification

These two abstract classes have several concrete classes that handle unicode character.


Some important Charcter stream classes.

Stream classDescription
BufferedReaderHandles buffered input stream.
BufferedWriterHandles buffered output stream.
FileReaderInput stream that reads from file.
FileWriterOutput stream that writes to file.
InputStreamReaderInput stream that translate byte to character
OutputStreamReaderOutput stream that translate character to byte.
PrintWriterOutput Stream that contain print() and println() method.
ReaderAbstract class that define character stream input
WriterAbstract class that define character stream output


Reading Console Input

We use the object of BufferedReader class to take inputs from the keyboard.

BufferedReader class explanation


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

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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