求质数方法大总结

 1 public class PrimeTest1
 2 {
 3     public static boolean isPrime(int numPrime)
 4     {
 5         for (int i = 2; i < numPrime; i++)
 6         {
 7             if (numPrime % i == 0)
 8             {
 9                 return false;
10             }
11         }
12         return true;
13     }
14     
15     public static int countPrime(int allPrime)
16     {
17         int count = 0;
18         
19         for (int i = 2; i < allPrime; i++)
20         {
21             if (isPrime(i) == true)
22             {
23                 count++;
24             }
25         }
26         
27         return count;
28     }
29     
30     
31     
32     public static void main(String[] args)
33     {
34         final int Nmax = 100000;
35         double startTime = System.currentTimeMillis();
36         int primeNum = PrimeTest1.countPrime(Nmax);
37         double timeSpent=(System.currentTimeMillis()-startTime)/1000;
38         
39         System.out.println("(method1)The prime numbers from 1 to "+Nmax+" is "+primeNum);
40         System.out.println("Time spent : "+timeSpent+" s");
41 
42     }
43 
44 }