Java.io.PushbackReader.unread() Method

Description

The java.io.PushbackReader.unread(char[] cbuf,int off,int len) method pushes back a portion of an array of characters by copying it to the front of the pushback buffer. After this method returns, the next character to be read will have the value cbuf[off], the character after that will have the value cbuf[off+1], and so forth.

Declaration

Following is the declaration for java.io.PushbackReader.unread() method

public void unread(char[] cbuf,int off,int len)

Parameters

• cbuf -- Character array to push back

• off -- Offset of first character to push back

• len -- Number of characters to push back

Return Value

This method does not return a value

Exception

• IOException -- If there is insufficient room in the pushback buffer, or if some other I/O error occurs

Example

The following example shows the usage of java.io.PushbackReader.unread() method.

package com.tutorialspoint;

import java.io.*;

public class PushbackReaderDemo {

   public static void main(String[] args) {

      String s = "Hello World";

      // create a new StringReader
      StringReader sr = new StringReader(s);

      // create a new PushBack reader based on our string reader
      PushbackReader pr = new PushbackReader(sr, 20);

      try {
         // read the first five chars
         for (int i = 0; i < 5; i++) {
            char c = (char) pr.read();
            System.out.print("" + c);
         }

         // change line
         System.out.println();

         // create a new array to unread
         char cbuf[] = {'w', 'o', 'r', 'l', 'd'};

         // unread into cbuf
         pr.unread(cbuf, 1, 4);

         // read 4 chars, which is what we unread from cbuf
         for (int i = 0; i < 4; i++) {
            char c = (char) pr.read();
            System.out.print("" + c);
         }

         // close the stream
         pr.close();

      } catch (IOException ex) {
         ex.printStackTrace();
      }
   }
}

Let us compile and run the above program, this will produce the following result:

Hello
orld