p007.java

package javasec;
import java.util.ArrayList;
public class p007
// from geeksforgeeks https://www.geeksforgeeks.org/program-to-find-the-nth-prime-number/
{
	static int MAX_SIZE = 1000005;
	 
	
	static ArrayList<Integer> primes =
	   new ArrayList<Integer>();
	 
	void SieveOfEratosthenes()
	{
		// Create a boolean array "IsPrime[0..MAX_SIZE]"
		// and initialize all entries it as true.
		// A value in IsPrime[i] will finally be false
		// if i is Not a IsPrime, else true.
		boolean [] IsPrime = new boolean[MAX_SIZE];
		 
		for(int i = 0; i < MAX_SIZE; i++)
			IsPrime[i] = true;
		 
		for (int p = 2; p * p < MAX_SIZE; p++)
		{
			// If IsPrime[p] is not changed,
			// then it is a prime
			if (IsPrime[p] == true)
			{
				// Update all multiples of p greater than or
				// equal to the square of it
				// numbers which are multiple of p and are
				// less than p^2 are already been marked.
				for (int i = p * p; i < MAX_SIZE; i += p)
					IsPrime[i] = false;
			}
		}
	 
		// Store all prime numbers
		for (int p = 2; p < MAX_SIZE; p++)
		if (IsPrime[p] == true)
				primes.add(p);
	}
	public int run() {
		SieveOfEratosthenes();
		return primes.get(10000);
	}
	public static void main (String[] args) {
		System.out.println(new p007().run());
	}
}