Java.io.PushbackReader.unread() Method

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Description

The java.io.PushbackReader.unread(int c) method pushes back a single character by copying it to the front of the pushback buffer. After this method returns, the next character to be read will have the value (char)c.

Declaration

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

public void unread(int c)

Parameters

c − The int value representing a character to be pushed back.

Return Value

This method does not return a value.

Exception

IOException − If the pushback buffer is full, 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();

         // unread a character
         pr.unread('F');

         // read the next char, which is the one we unread
         char c = (char) pr.read();

         // print that character
         System.out.println("" + 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
F