java编程求出2~N之间的所有素数..N由键盘输入. (麻烦给个代码)

package number11;

import
import
import

public class Num7 {

    /**
     * @param args
     * @throws IOException
     * @throws NumberFormatException
     */
    public static void main(String[] args) throws NumberFormatException, IOException {
        // TODO Auto-generated method stub
        
    int j=0;int m=2,n;
    
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    System.out.println("请输入数值n:");
    n= Integer.parseInt(br.readLine());
    for(m=2;m<=n;m++)
    {
        boolean flag=true;//必须放在这里，每次循环初始化
   
        for(int i=2;i<=Math.sqrt(m);i++)
        {
            if(m%i==0)
            {
                flag=false;
                break;
            }
        }
        if(flag)
        {
            j++;System.out.println(" "+m);}
    }
    System.out.println("共"+j+"个");
}
}