Java Tutorial : Java IO (Java PushbackInputStream) ~ foundjava

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Java Tutorial : Java IO (Java PushbackInputStream) 

Java Tutorial : Java IO (Java PushbackInputStream) 

Java Tutorial : Java IO (Java PushbackInputStream) 

myfile.txt

Hello world

PushbackInputStreamDemo.java

import java.io.FileInputStream;
import java.io.IOException;
import java.io.PushbackInputStream;

public class PushbackInputStreamDemo
{

    public static void main(String[] args) throws IOException
    {
        FileInputStream fileInputStream = null;
        PushbackInputStream pushbackInputStream = null;
        try
        {
            fileInputStream = new FileInputStream("myfile.txt");
            pushbackInputStream = new PushbackInputStream(fileInputStream);

            /*
             * Reads the next byte of data from this input
             * stream.
             */
            int data = pushbackInputStream.read();
            System.out.println((char) data);

            /*
             * Pushes back a byte by copying it to the front
             * of the pushback buffer.
             */
            pushbackInputStream.unread(data);

            data = pushbackInputStream.read();
            System.out.println((char) data);

        }
        finally
        {
            if (pushbackInputStream != null)
            {
                /*
                 * Closing a pushbackInputStream will also
                 * close the FileInputStream instance from
                 * which the PushbackReader is reading.
                 */
                pushbackInputStream.close();
            }
        }

    }

}

Output

H
H

Refer: 
https://docs.oracle.com/javase/8/docs/api/java/io/PushbackInputStream.html

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