Determine Prime number with the sieve of Eratosthenes in Java in java ?

import java.util.ArrayList;
import java.util.List;

public class DeterminePrime{

public static List<Integer> calcPrimeNumbers(int n) {
boolean[] isPrimeNumber = new boolean[n + 1]; // boolean defaults to
// false
List<Integer> primes = new ArrayList<Integer>();
for (int i = 2; i < n; i++) {
isPrimeNumber[i] = true;
}
for (int i = 2; i < n; i++) {
if (isPrimeNumber[i]) {
primes.add(i);
// Now mark the multiple of i as non-prime number
for (int j = i; j * i <= n; j++) {
isPrimeNumber[i * j] = false;
}
}

}

return primes;
}

public static void main(String[] args) {
List<Integer> calcPrimeNumbers = calcPrimeNumbers(21);
for (Integer integer : calcPrimeNumbers) {
System.out.println(integer);
}
System.out.println("Prime counting function (Pie(N)) : "
+ calcPrimeNumbers.size());
}

}


Below is the output...

2
3
5
7
11
13
17
19
Prime counting function (Pie(N)) : 8