Java Program to Implement Sieve of Eratosthenes to Generate Prime Numbers Between Given Range

// Java Program to Generate Prime
// Numbers Between Given Range
class GFG {
    public static boolean isprime(int n)
    {
        if (n == 1)
            return false;

        for (int i = 2; i <= Math.sqrt(n); i++)

            // Check if a number has factors
            // its not prime and return 0
            if (n % i == 0)
                return false;
      
        // Check if a number dont 
        // have any factore
        // its prime and return 1
        return true;
    }
    public static void main(String[] args)
    {
        
        // Suppose we want to print
        // prime no.  from 1 to 20
        int from = 1, to = 20, k = 0;
        for (int i = from; i <= to; i++)
            if (isprime(i))
                System.out.print(" " + i);
    }
}

// Java Program to Implement 
// Sieve of eratosthenes
// to Generate Prime Numbers 
// Between Given Range
import java.util.*;
class GFG {

    public static void main(String[] args)
    {
        int from = 1, to = 20, i;
        boolean[] a = new boolean[to + 1];
        Arrays.fill(a, true);

        // 0 and 1 are not prime
        a[0] = false;
        a[1] = false;
        for (i = 2; i <= Math.sqrt(to); i++)

            // Check if number is prime
            if (a[i])
                for (int j = i * i; j <= to; j += i) {
                    a[j] = false;
                }
        for (i = from; i <= to; i++) {

            // Printing only prime numbers
            if (a[i])
                System.out.print(" " + i);
        }
    }
}