java 快速求素数

 1 package test ; 
 2 import java.util.Scanner ;
 3 public class hello
 4 {
 5     public static void main(String [] args)
 6     {
 7         Scanner read = new  Scanner(System.in);
 8         while(read.hasNext())
 9         {
10         String rr = read.next();
11         int maxn=Integer.parseInt(rr);
12         boolean isprime[] = new boolean [maxn] ; //Java 默认初始化值为false
13     //    int prime[] =new int [maxn/3];
14         int i,j;
15         for( i=2 ; i<maxn ; i++ )
16         {
17             if(!isprime[i])
18             {
19                 for(j=i+i ;j<maxn ;j+=i)
20                        isprime[j]=true;
21             }
22         }
23        for(i=2 ;i<maxn ;i++)
24        {
25            if(!isprime[i])
26           System.out.print(" "+i);
27        }
28       System.out.println();
29     }
30     }
31 }