writeprimes.java

21天学会JAVA

import java.io.*;

class WritePrimes {
    public static void main(String[] arguments) {
        int[] primes = new int[400];
        int numPrimes = 0;
        // candidate: the number that might be prime
        int candidate = 2;
        while (numPrimes < 400) {
            if (isPrime(candidate)) {
                primes[numPrimes] = candidate;
                numPrimes++;
            }
            candidate++;
        }

        try {
            // Write output to disk
            FileOutputStream file = new
                FileOutputStream("400primes.dat");
            BufferedOutputStream buff = new
                BufferedOutputStream(file);
            DataOutputStream data = new
                DataOutputStream(buff);

            for (int i = 0; i < 400; i++)
               data.writeInt(primes[i]);
            data.close();
        } catch (IOException e) {
            System.out.println("Error -- " + e.toString());
        }
    }

    public static boolean isPrime(int checkNumber) {
        double root = Math.sqrt(checkNumber);
        for (int i = 2; i <= root; i++) {
            if (checkNumber % i == 0)
                return false;
        }
        return true;
    }
}