Overview of streams

Overview

1. A stream can be defined as a sequence of data. 
2. Input Stream is used to read data from a source and the Output Stream is used for writing data to a destination.
3. Java provides strong but flexible support for I/O related to Files and networks.

Byte stream is defined by using two abstract class at the top of hierarchy, they are Input Stream and Output Stream.

Java byte streams are used to perform input and output of 8-bit bytes. Though there are many classes related to byte streams but the most frequently used classes are ,FileInputStream and FileOutputStream

These two abstract classes have several concrete classes that handle various devices such as disk files, network connection etc.

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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.

Example,

import java.io.*;

public class CopyFile {
   public static void main(String args[]) throws IOException
   {
      FileInputStream in = null;
      FileOutputStream out = null;

      try {
         in = new FileInputStream("input.txt");
         out = new FileOutputStream("output.txt");
         
         int c;
         while ((c = in.read()) != -1) {
            out.write(c);
         }
      }finally {
         if (in != null) {
            in.close();
         }
         if (out != null) {
            out.close();
         }
      }
   }
}

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Character Stream Classes

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

Java Byte streams are used to perform input and output of 8-bit bytes, where as JavaCharacter streams are used to perform input and output for 16-bit unicode.

 Though there are many classes related to character streams but the most frequently used classes are ,FileReader and FileWriter.

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

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Some important Character 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

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Reading Console Input

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

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

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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);
 }
}

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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(); }
 }
}

Example

import java.io.*;

public class CopyFile {
   public static void main(String args[]) throws IOException
   {
      FileReader in = null;
      FileWriter out = null;

      try {
         in = new FileReader("input.txt");
         out = new FileWriter("output.txt");
         
         int c;
         while ((c = in.read()) != -1) {
            out.write(c);
         }
      }finally {
         if (in != null) {
            in.close();
         }
         if (out != null) {
            out.close();
         }
      }
   }
}

Byte vs characters streams,