moreprimes.java

Java2入门经典第四章源码

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

    outer:
    for( ; count < primes.length; number += 2)
    {
      // The maximum divisor we need to try is square root of number
      long limit = (long)Math.ceil(Math.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] == 0)             // Is it an exact divisor?
          continue outer;              // yes, try the next number

      primes[count++] = number;               // We got one!
    }

    for(int i=0; i < primes.length; i++)
      System.out.println(primes[i]);          // Output all the primes
  }
}