With its I/O package, Java includes a variety of Streams that make it easier for the user to carry out any input-output tasks. For complete I/O operation execution, these streams support all object, data-type, character, and file kinds.

Stream:

A data stream is a collection of data. A stream in Java is made up of bytes. It resembles a flowing stream of water, which is why it is called a stream.

Before looking at different input and output streams, let’s take a closer look at the three standard or default streams that Java offers and are also the most widely used:

• System.in: The standard input stream, known as system.in, reads characters from the keyboard and other standard input devices.
• System.out: It is the standard output stream used to display a program’s output on an output device, such as a computer screen.
• System.err: This is the standard error stream used to print any standard output device or a computer screen with any error information that a program might produce.

Under the java.io package, Stream is contained by Java. Java specifies two different stream types. It’s them,

• Byte stream: A convenient method for processing byte input and output is the byte stream.
• Character Stream: It offers a practical method for managing character input and output. Character stream can be internationalized because it uses Unicode.

Java Byte Stream Class:

The two abstract classes InputStream and OutputStream at the top of the hierarchy are used to define bytes streams.

OutputStream:

An output stream is used by a Java application to write data to a destination, such as a file, an array, a peripheral device, or a socket.

Useful methods of OutputStream:

• public void write(int)throws IOException– write a byte to the active output stream using this method.
• public void write(byte[])throws IOException– is used to write an array of bytes to the current output stream.
• public void flush()throws IOException– flushes the current output stream.
• public void close()throws IOException- is used to close the current output stream.

InputStream:

A Java application utilizes an input stream when reading data from a source—a file, an array, a peripheral device, or a socket.

methods of InputStream:

• public abstract int read()throws IOException- scans the incoming data stream’s subsequent byte. At the conclusion of the file, it returns 1.
• public int available()throws IOException– returns an estimate of the number of bytes that can be read from the current input stream.
• public void close()throws IOException– is used to close the current input stream.

Example:

// Java Program illustrating the
// Byte Stream to copy
// contents of one file to another file.
import java.io.*;
public class Coderz {
	public static void main(
		String[] args) throws IOException
	{

		FileInputStream sourceStream = null;
		FileOutputStream targetStream = null;

		try {
			sourceStream
				= new FileInputStream("sorcefile.txt");
			targetStream
				= new FileOutputStream("targetfile.txt");

			// Reading source file and writing
			// content to target file byte by byte
			int temp;
			while ((
					temp = sourceStream.read())
				!= -1)
				targetStream.write((byte)temp);
		}
		finally {
			if (sourceStream != null)
				sourceStream.close();
			if (targetStream != null)
				targetStream.close();
		}
	}
}

Output:

Shows contents of file test.txt 

Java Character Stream Class:

Reader and Writer are the two abstract classes at the top of the hierarchy used to define character streams.

Stream class	Description
BufferedReader	It is used to handle buffered input stream.
FileReader	This is an input stream that reads from a file.
InputStreamReader	This input stream is used to translate byte to character.
OutputStreamReader	This output stream is used to translate character to byte.
Reader	This is an abstract class that defines character stream input.
PrintWriter	This contains the most used print() and println() method
Writer	This is an abstract class that defines character stream output.
BufferedWriter	This is used to handle the buffered output stream.
FileWriter	This is used to output stream that writes to the file.

Example:

import java. Io *;
// Java Program illustrating that
// we can read a file in a human-readable
// format using FileReader
class Coderz
{
  public static void main(String[] args)
  {
    try
    {
      File fl = new File("d:/myfile.txt");
       // Reading sourcefile and
            // writing content to target file
            // character by character.
      BufferedReader br = new BufferedReader(new FileReader(fl)) ;
      String str;
      while ((str=br.readLine())!=null)
      {
        System.out.println(str);
      }
      br.close();
      fl.close();
       // Closing stream as no longer in use
    }
    catch(IOException  e) { 
      e.printStackTrace(); 
    }
  }
}

Output:

Shows contents of file

Note: also read about the Autoboxing and Unboxing in Java

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