Stream and File Concept In Java

Stream facilitate transporting data from one place to another place. Different streams are needed to send or receive data through different sources, such as to receive data from the keyboard, we need s stream and to send data to a file, we need another.without streams, it is not possible to move data in java.

Stream:-

A Stream carries data just as a water pipe carries water from one place to another place. There are two categories of streams namely 'input stream' and 'output stream '. input streams are the stream which receives or read data while output streams are the stream which sends data or write the data . all streams represented by classes java.io package.

Now let us see how stream works. we know an input stream reads. so to read data from keyboard we can attach the keyboard to an input stream. so that the stream can read the typed on the keyboard.

   DataInputStream dis=new DataInputStream(System.in);

In the above statement, we are attaching a keyboard to DataInputStream object. the keyboard is represented by System.in. Now DatatStream objects can read data coming from the keyboard. here System is a class and 'in' is a field of System class. In fact, there are three fields of system class.

1. System.in represents InputStream object. this object represents standard input device by default Keyboard.
2. System.out represents the PrintStream object. this object represents standard output device by default, that is the monitor.
3. System.err represents the PrintStream object. this object represents by default standard output device that is monitor.

so we can also use System.err to print something on the monitor just like System.out    

please observe the above keyboards is represented by System.in which internally creates an object of InputStream class. it means is an InputStream. Similarly the monitor is represented by PrintStream. In this way, Streams represent input/output devices in Java. even we change the keyboard or monitor, we can still use the same streams to handle those devices. in this way, streams are useful to handle the input/output devices irrespective of their make.

 this is an example how to create and write file in java.

import java.io.*;
class CreateFile{
public static void main(String arg[]) throws IOException
   {
          //use to read data from keybord   
         DataInputStream dis=new DataInputStream(System.in);
         
          // for create file
          FileOutputStream fileStream =new FileOutputStream("myFile.txt");
           
         System.out.println("Enter test (@ at the end)");
         char ch;
           //writing data into file from keyboard
         while((ch=(char)dis.read())!='@'){
          fileStream.write(ch);
            } 
          fileStream.close();  


   }
}