static void sieve(int n,boolean[] primes)

{

for (int i = 0; i <= n; i++)

{

primes[i]=true; //first step is to initialize all the values with true

}

for(int i=2;i*i<=n;i++)

{

if(primes[i]==true) //if no. @ index is prime then sure its multiples cannot be prime so that is done in nested loop...we are making multiples false as they are not prime.

{

for(int j=i*2;j<=n;j+=i) //initializing is done from j=i*2 means we are starting from the multiples of that no..j will definitely move as j=j+i...as we are concerned with multitples... for example muliples of 2 are 4,6,8...so on at each iterastion +2 is increasing

{

primes[j]=false; //simply make all the multiples of that no. false else they cannot be prime very obvious

}

}

}

for(int i=2;i<=n;i++)

{

if(primes[i]==true)

{

System.out.print(i + " ");

}

}

}

public static void main(String[] args) {

int n=50;

boolean[] primes=new boolean[n+1]; //because we have to include 50 in the boolean array as well..and as the index starts with zero it will just add uptil 39 only...so the size is 1+ the n.

sieve(n, primes);

}