Sieve of Eratosthenes

import java.util.ArrayList;
import java.util.Scanner;

public class more_Optimised_Eratosthenes_sieve {

    static final int M = 1000000;
    static boolean[] mark;

    public static void main(String[] args) {
        ArrayList<Integer> primeList = new ArrayList<>();
        Scanner scan = new Scanner(System.in);

        int n = scan.nextInt();
        mark = new boolean[M];

        // call the Eratosthenes sieve.
        sieveEra(n);

        for(int i = 1; i <= n; i++)
            if(isPrime(i))
                primeList.add(i);

        System.out.println(primeList);

        scan.close();
    }

    private static boolean isPrime(int n)
    {
        if(n < 2)
            return false;
        if(n == 2)
            return true;
        if(n % 2 == 0)
            return false;

        return mark[n] == false;
    }

    private static void sieveEra(int n)
    {
        for(int i = 3; i*i <= n; i += 2)   // run upto sqrt(n)
        {
            if(mark[i] == false)
            {
                for(int j = i*i; j <= n; j += 2*i)
                    mark[j] = true;
            }
        }
    }

}