prime numbers program in java

/**
 * @author lautturi.com 
 * Java example: check whether a number is prime number or not in java
 */

import java.util.*;

public class Lautturi {
	public static boolean isPrimeNumber(int num) {
		if(num == 0 || num == 1)
			return false;
		if(num == 2)
			return true;
 
		for(int div = 2; div*div <= num; div++) {
			if(num % div==0)
				return false;
		}
		return true;
	}

	public static void main(String[] args) {
		for (int num = 0; num < 20; num++) {
			if (isPrimeNumber(num)) {
				System.out.println(num + " is a prime number. ");
			}
		}
	}
}

output:

2 is a prime number. 
3 is a prime number. 
5 is a prime number. 
7 is a prime number. 
11 is a prime number. 
13 is a prime number. 
17 is a prime number. 
19 is a prime number.