Primes.java Source code

Introduction

Here is the source code for Primes.java

Source

/* Compute prime numbers, after Knuth, Vol 1, Sec 1.3.2, Alg. "P".
 * Unlike Knuth, I don't build table formatting into
 * computational programs; output is one per line.
 * <p>
 * Note that there may be more efficient algorithms for finding primes.
 * Consult a good book on numerical algorithms.
 * @author Ian Darwin
 */
public class Primes {
    /** The default stopping point for primes */
    public static final long DEFAULT_STOP = 4294967295L;
    /** The first prime number */
    public static final int FP = 2;

    static int MAX = 10000;

    public static void main(String[] args) {
        long[] prime = new long[MAX];

        long stop = DEFAULT_STOP;
        if (args.length == 1) {
            stop = Long.parseLong(args[0]);
        }

        prime[1] = FP; // P1 (ignore prime[0])
        long n = FP + 1; // odd candidates
        int j = 1; // numberFound

        boolean isPrime = true; // for 3

        do {

            if (isPrime) {
                if (j == MAX - 1) {
                    // Grow array dynamically if needed
                    long[] np = new long[MAX * 2];
                    System.arraycopy(prime, 0, np, 0, MAX);
                    MAX *= 2;
                    prime = np;
                }
                prime[++j] = n; // P2
                isPrime = false;
            }
            n += 2; // P4

            for (int k = 2; k <= j && k < MAX; k++) { // P5, P6, P8
                long q = n / prime[k];
                long r = n % prime[k];
                if (r == 0) {
                    break;
                }
                if (q <= prime[k]) { // P7
                    isPrime = true;
                    break;
                }
            }

        } while (n < stop); // P3

        for (int i = 1; i <= j; i++)
            System.out.println(prime[i]);
    }
}