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SecureRandom nextBytes() method in Java with Examples

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The nextBytes() method of java.security.SecureRandom class is used to generate a user-specified number of random bytes. If a call to setSeed had not occurred previously, the first call to this method forces this SecureRandom object to seed itself. This self-seeding will not occur if setSeed was previously called. Syntax:
public void nextBytes(byte[] bytes)
Parameters: This method takes the array to be filled in with random bytes as parameter . Note:
  1. The programs will not run on online IDE.
  2. Every time Secure Random class will generate random output.
Below are the examples to illustrate the nextBytes() method: Example 1:
// Java program to demonstrate
// nextBytes() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // creating the object of SecureRandom
            SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
  
            // Declaring the string variable
            String str = "Tajmahal";
  
            // Declaring the byte Array
            // converting string into byte
            byte[] b = str.getBytes();
  
            // printing the byte array
            System.out.println("Byte array before operation : " + Arrays.toString(b));
  
            // generating user-specified number of random bytes
            // using nextBytes() method
            sr.nextBytes(b);
  
            // printing the new byte array
            System.out.println("Byte array after operation : " + Arrays.toString(b));
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
        catch (ProviderException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

                    
Output:
Byte array before operation : [84, 97, 106, 109, 97, 104, 97, 108]
Byte array after operation : [-79, -110, -18, -31, -54, -36, 63, -61]
Note: The following program throws the following Exception on GeeksForGeeks IDE but it will run efficiently on any Command Prompt(JDK)
Exception thrown : java.security.ProviderException: init failed
Example 2:
// Java program to demonstrate
// nextBytes() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // creating the object of SecureRandom
            SecureRandom sr = new SecureRandom(new byte[] { 1, 2, 3, 4 });
  
            // Declaring the string variable
            String str = "Tajmahal";
  
            // Declaring the byte Array b
            byte[] b = str.getBytes();
  
            // printing the byte array
            System.out.println("Byte array before operation : " + Arrays.toString(b));
  
            // generating user-specified number of random bytes
            // using nextBytes() method
            sr.nextBytes(b);
  
            // printing the new byte array
            System.out.println("Byte array after operation : " + Arrays.toString(b));
        }
  
        catch (ProviderException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

                    
Output:
Byte array before operation : [84, 97, 106, 109, 97, 104, 97, 108]
Byte array after operation : [-14, 77, 123, 121, 116, 50, -89, -86]


Last Updated : 04 Dec, 2018
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