PushbackReader unread(int) in Java

unread(int): This method is available in the java.io.PushbackReader class of Java.

Syntax:

void java.io.PushbackReader.unread(int c) throws IOException

This method takes one argument. This 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.

Parameters: One parameter is required for this method.

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

Returns: NA

Throws:

1. IOException - If the pushback buffer is full, or if some other I/O error occurs

Approach 1: When no exception

Java

import java.io.IOException;
import java.io.PipedReader;
import java.io.PushbackReader;
import java.io.Reader;

public class PushbackReaderunread2 {
    public static void main(String[] args) throws IOException {

        Reader in = new PipedReader();
        PushbackReader pushbackReader = new PushbackReader(in);

        int c = 'A';
        pushbackReader.unread(c);

        System.out.println("Successfully unread");
        pushbackReader.close();
    }
}

Output:

Successfully unread

Approach 2: IOException

Java

package com.PushbackReader;

import java.io.IOException;
import java.io.PipedReader;
import java.io.PushbackReader;
import java.io.Reader;

public class PushbackReaderunread2 {
    public static void main(String[] args) throws IOException {

        Reader in = new PipedReader();
        PushbackReader pushbackReader = new PushbackReader(in);

        int c = 'A';
        pushbackReader.close();
        pushbackReader.unread(c);

        System.out.println("Successfully unread");

    }
}

Output:

Exception in thread "main" java.io.IOException: Stream closed
	at java.base/java.io.PushbackReader.ensureOpen(PushbackReader.java:73)
	at java.base/java.io.PushbackReader.unread(PushbackReader.java:154)
	at com.PushbackReader.PushbackReaderunread2.main(PushbackReaderunread2.java:16)

Some other methods of PushbackReader

close(): This method closes the stream and releases any system resources associated with it.

mark(int): This method marks the present position in the stream.

markSupported(): This method tells whether this stream supports the mark() operation, which it does not.

PushbackReader(Reader): This method creates a new pushback reader with a one-character pushback buffer.

PushbackReader(Reader, int): This method creates a new pushback reader with a pushback buffer of the given size.

read(): This method reads a single character.

read(char[], int, int): This method reads characters into a portion of an array.

ready(): This method tells whether this stream is ready to be read.

reset(): This method resets the stream.

skip(long): This method skips characters

unread(char[]): This method pushes back an array of characters by copying it to the front of the pushback buffer.

unread(int): This method pushes back a single character by copying it to the front of the pushback buffer.

unread(char[], int, int):  This method pushes back a portion of an array of characters by copying it to the front of the pushback buffer.