BigInteger prime value

In this chapter you will learn:

How to know if a BigInteger value prime
How to generate a prime number from BigInteger

Is a BigInteger value prime

boolean isProbablePrime(int certainty) returns true if this BigInteger is probably prime, false if it's definitely composite.

import java.math.BigInteger;
/*from   j  a v  a2s  .c  o  m*/
public class Main {
  public static void main(String args[]) {
    BigInteger n = new BigInteger("1000000000000");
    BigInteger one = new BigInteger("1");
    while (!n.isProbablePrime(7))
      n = n.add(one);
    System.out.println(n.toString(10) + " is probably prime.");
    System.out.println("It is " + n.bitLength() + " bits in length.");
  }
}

The output:

Get a prime number from BigInteger

probablePrime(int bitLength, Random rnd) returns a positive BigInteger that is probably prime, with the specified bitLength.

import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.Random;
//  j av a2 s . co  m
public class MainClass {
  public static void main(String[] unused) {
    Random prng = new SecureRandom();  // self-seeding
    System.out.println(BigInteger.probablePrime(10, prng));
  }
}