JAVA prime number

Create a prime number

import java.math.*;
import java.util.*;

class CreatePrime
{
public static void main( String args[]) {
int bitLength = 128;
int certainty = 10;

    BigInteger prime = new BigInteger( bitLength, certainty, new Random());
    System.out.println( prime.toString());
    }
}

Test a number is it a prime

java.math.BigInteger
public boolean isProbablePrime(int certainty)

Returns true if this BigInteger is probably prime, false if it's definitely composite. The certainty parameter is a measure of the uncertainty that the caller is willing to tolerate: the method returns true if the probability
that this number is is prime exceeds 1 - 1/2**certainty. The execution time is proportional to the value of the certainty parameter.