```
public int countPrimes(int n) {
final boolean[] notPrime = new boolean[n];
int count = 0;
for (int i = 2; i < n; i++) {
if (notPrime[i] == false) {
count++;
for (int j = 2; i * j < n; j++) {
notPrime[i * j] = true;
}
}
}
return count;
}
```