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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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/*
 * This source code is provided to illustrate the usage of a given feature
 * or technique and has been deliberately simplified. Additional steps
 * required for a production-quality application, such as security checks,
 * input validation and proper error handling, might not be present in
 * this sample code.
 */
package stream.parallel;

import java.math.BigInteger;
import java.util.Random;
import java.util.stream.LongStream;

/**
 * This demo shows how to use the parallel mode to find several number of
 * unknown length�prime number. The process easily use new Random.LongStream
 * generates a desired length stream. Following with filter operation. Here
 * input length is desirable long stream length instead of number of prime
 * number.
 *
 * @author tyan
 */
public class RandomPrimeNumber {
    /**
     * By default we only calculate at most 64 numbers once..
     */
    private final static long RANGE_SIZE = 1 << 6;

    /**
     * Try to get length from command line. Use the length to create random long
     * stream, that integer's digit is length.
     *
     * @param args This has to be a 1-element or 2-elements array, The first
     * element must be a positive number, which equals to length of generated
     * prime number stream. Second element is optional, it will be used as how
     * many prime number that will be generated if it's set.
     */
    public static void main(String[] args) {
        if (args.length != 1 && args.length != 2) {
            usage();
            return;
        }
        try {
            int length = Integer.parseInt(args[0]);
            if (length > 16) {
                System.out.println("Can calculate maximun only l6 digits "
                        + "prime number");
                return;
            }
            long numberOfPrime = RANGE_SIZE;
            if (args.length == 2) {
                numberOfPrime = Long.parseLong(args[1]);
            }
            long minNDigit = BigInteger.valueOf(10L).pow(length - 1).longValue();
            long maxNDigit = BigInteger.valueOf(10L).pow(length).longValue();

            new Random(System.currentTimeMillis()).
                    longs(numberOfPrime, minNDigit, maxNDigit).
                    filter(N -> isPrime(N)).
                    forEach(System.out::println);
        } catch (NumberFormatException nfe) {
            usage();
        }
    }

    /**
     * Decide if a BigInteger is a prime number
     *
     * @param integer a number
     * @return true if integer is a prime number false if integer is not a prime
     * number
     */
    private static boolean isPrime(long number) {
        //This is a parall version that checks if a number is a prime number
        return !LongStream.range(2L, Math.round(Math.sqrt(number))).parallel().
                anyMatch(divisor -> number % divisor == 0);
    }

    /**
     * Usage of this program
     */
    public static void usage() {
        System.out.println("Usage: java RandomPrimeNumber lentgh［size]");
        System.out.println("length is a positive integer not greater than 16");
        System.out.println("size is a positive integer");
    }
}