[Hackerrank] Prime Number Less Than N

static int getNumberOfPrimes(int N) {
        int n = N+1;//to include 0 as the first number for easy index operations later
        final boolean a[] = new boolean[n]; //Initialized to null by default.
        Arrays.fill(a, true);  

        a[0] = false;
        a[1] = false; 

        for (int i = 2; i < n / 2; ++i)
        {
            if (a[i])
            {
                for (int j = i + i; j < n; j += i)
                    a[j] = false;
            }
        } 

        int count = 0;for(int i = 2;i<n;++i)
        {
            if(a[i])
            {
                //System.out.print(i+",");
                ++count;
            }
        }
        return count;
    }