MorePrimes.java

package ch01basic;

import static java.lang.Math.ceil;
import static java.lang.Math.sqrt;

public class MorePrimes {
    public static void main(String[] args) {
        long[] primes = new long[20];      // Array to store primes
        primes[0] = 2L;                    // Seed the first prime
        primes[1] = 3L;                    // and the second
        int count = 2;                     // Count of primes found - up to now,
        // which is also the array index
        long number = 5L;                  // Next integer to be tested

        outer:
        for (; count < primes.length; number += 2L) {
            // The maximum divisor we need to try is square root of number
            long limit = (long) ceil(sqrt((double) number));

            // Divide by all the primes we have up to limit
            for (int i = 1; i < count && primes[i] <= limit; ++i) {
                if (number % primes[i] == 0L) {   // Is it an exact divisor?
                    continue outer;              // Yes, so try the next number
                }
            }
            primes[count++] = number;        // We got one!
        }

        for (long n : primes) {
            System.out.println(n);           // Output all the primes
        }
    }
}