The push back input stream is a class used to unread data, to push back byte data into stream. The main functionality of this is to interpret the present byte into the stream. If the unread() method is called then, it pushes the data into the push back  input stream. After again calling read() method at that time the push backed data will reads first. The last pushed byte data will be reads first. The push back data limit is also initialized with constructor in push back input stream.

Java.io PushbackInputStream class is declared below: Public class PushbackInputStream extends FilterInputStream

Java.io PushBackInputStream class fields are:

• Protected InputStream in : The field represents the current stream have to filter.
• Protected byte [] buf : The field represents to the internal(push back) buffer where actually the data stored.
• Protected int pos : The field represents to the position of push back input stream buffer to read that coming byte.

From the following classes, methods are inherited to the push back input stream class.

• Java.io.Object
• Java.io.FilterInputStream

Usage of void unread(byte b) method. [c]import java.io.*; public class PushbackInputStream { public static void main(String[] args) { // To declare the buffer and initialize its size: byte[] arrByte = new byte[1024]; // creating a new byte array byte[] byteArray = new byte[]{'H', 'E', 'L', 'L', 'O', 'W', 'O', 'R', 'L', 'D'}; // creating a new PushbackInputStream instance for specified stream InputStream is = new ByteArrayInputStream(byteArray); PushbackInputStream pis = new PushbackInputStream(is, 10); try { // To read from the buffer one character at a time for (int i = 0; i < byteArray.length; i++) { // To read a char into our array arrByte[i] = (byte) pis.read(); // To display the read byte System.out.println((char) arrByte[i]); } // creating a new byte array to be unread byte[] b = {'S', 'P', 'L', 'E', 'S', 'S', 'O', 'N', 'S', '.'}; // To unread the byte array pis.unread(b); // TO read again from the buffer one character at a time for (int i = 0; i < byteArray.length; i++) { // To read a char into array arrByte[i] = (byte) pis.read(); // To display the byte reads System.out.print((char) arrByte[i]); } } catch (Exception ex) { ex.printStackTrace(); } } }[/c] Output Following is the result will be displayed. [c] HELLOWORLD SPLESSONS.[/c] Usage of void unread(byte[] b, int off, int n) method. [c]import java.io.*; public class PushbackInputStream { public static void main(String[] args) { // To declare a buffer and initialize its size: byte[] arrByte = new byte[1024]; // creating a new byte array byte[] byteArray = new byte[]{'H', 'e', 'l', 'l', 'o'}; // creating a new PushbackInputStream instance for specified stream InputStream is = new ByteArrayInputStream(byteArray); PushbackInputStream pis = new PushbackInputStream(is); try { // To read from the buffer one character at a time for (int i = 0; i < byteArray.length; i++) { // To read a char into array arrByte[i] = (byte) pis.read(); // To display the byte read System.out.print((char) arrByte[i]); } System.out.println("\n"); // To close the stream pis.close(); System.out.println("Stream closed."); } catch (Exception ex) { ex.printStackTrace(); } } }[/c] Output Following is the result will be displayed. [c] Hello Stream closed. [/c]

• The push back input stream is a class used to unread data, to push back byte data into stream.
• The main functionality of this is to interpret the present byte into the stream.
• When the unread() method is called then, it pushes the data into the push back input stream.
• The last pushed byte data will be reads first.
• The push back data limit is also initialized with constructor in push back input stream.