Método MessageDigest reset() en Java con ejemplos

El método reset() de la clase java.security.MessageDigest se utiliza para restablecer el valor de resumen de mensaje actual al valor de resumen de mensaje predeterminado de este objeto MessageDisgest.
Sintaxis: 
 

public void reset()

Valor devuelto: este método no tiene nada que devolver.
A continuación se muestran los ejemplos para ilustrar el método reset() :
Ejemplo 1: 
 

// Java program to demonstrate
// toString() method
 
import java.security.*;
import java.nio.*;
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
 
            byte[] barr = { 10, 20, 30, 40 };
 
            // creating object of MessageDigest
            MessageDigest msd1
                = MessageDigest.getInstance("MD5");
 
            // display the digest value before Updation
            System.out.println("MessageDigest before update : "
                               + (ByteBuffer.wrap(
                                      msd1.digest()))
                                     .getShort());
 
            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.wrap(barr);
 
            // update MessageDigest value
            // using update() method
            msd1.update(bb);
 
            // display the digest value before Updation
            System.out.println("\nMessageDigest after update : "
                               + (ByteBuffer.wrap(
                                      msd1.digest()))
                                     .getShort());
 
            // reset MessageDigest value
            // using reset() method
            msd1.reset();
 
            // display the digest value after reset
            System.out.println("\nMessageDigest after reset : "
                               + (ByteBuffer.wrap(
                                      msd1.digest()))
                                     .getShort());
        }
 
        catch (NoSuchAlgorithmException e) {
 
            System.out.println("Exception thrown : " + e);
        }
        catch (ProviderException e) {
 
            System.out.println("Exception thrown : " + e);
        }
    }
}

MessageDigest before update : -11235

MessageDigest after update : 30835

MessageDigest after reset : -11235

Ejemplo 2: 
 

// Java program to demonstrate
// toString() method
 
import java.security.*;
import java.nio.*;
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
 
            byte[] barr = { 10, 20, 30, 40 };
 
            // creating object of MessageDigest
            MessageDigest msd1
                = MessageDigest.getInstance("SHA-256");
 
            // display the digest value before Updation
            System.out.println("MessageDigest before update : "
                               + (ByteBuffer.wrap(
                                      msd1.digest()))
                                     .getShort());
 
            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.wrap(barr);
 
            // update MessageDigest value
            // using update() method
            msd1.update(bb);
 
            // display the digest value before Updation
            System.out.println("\nMessageDigest after update : "
                               + (ByteBuffer.wrap(
                                      msd1.digest()))
                                     .getShort());
 
            // reset MessageDigest value
            // using reset() method
            msd1.reset();
 
            // display the digest value after reset
            System.out.println("\nMessageDigest after reset : "
                               + (ByteBuffer.wrap(
                                      msd1.digest()))
                                     .getShort());
        }
 
        catch (NoSuchAlgorithmException e) {
 
            System.out.println("Exception thrown : " + e);
        }
        catch (ProviderException e) {
 
            System.out.println("Exception thrown : " + e);
        }
    }
}

MessageDigest before update : -7248

MessageDigest after update : 24403

MessageDigest after reset : -7248

Referencia:  
https://docs.oracle.com/javase/9/docs/api/java/security/MessageDigest.html#reset–