Sieve.java Source code

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Here is the source code for Sieve.java

Source

/*
   This program is a part of the companion code for Core Java 8th ed.
   (http://horstmann.com/corejava)
    
   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.
    
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
    
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

import java.util.*;

/**
 * This program runs the Sieve of Erathostenes benchmark. It computes all primes up to 2,000,000.
 * @version 1.21 2004-08-03
 * @author Cay Horstmann
 */
public class Sieve {
    public static void main(String[] s) {
        int n = 2000000;
        long start = System.currentTimeMillis();
        BitSet b = new BitSet(n + 1);
        int count = 0;
        int i;
        for (i = 2; i <= n; i++)
            b.set(i);
        i = 2;
        while (i * i <= n) {
            if (b.get(i)) {
                count++;
                int k = 2 * i;
                while (k <= n) {
                    b.clear(k);
                    k += i;
                }
            }
            i++;
        }
        while (i <= n) {
            if (b.get(i))
                count++;
            i++;
        }
        long end = System.currentTimeMillis();
        System.out.println(count + " primes");
        System.out.println((end - start) + " milliseconds");
    }
}