judgeprime.java

用java判断素数

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class JudgePrime
{
	public static boolean prime(int num)
	{
		int i;
		int half = (int)(Math.sqrt(num+0.0)+0.5);
		for(i=2;i<=half;i++)
		{
			if(num%i==0) return false;
		}
		return true;
	}
	public static void main(String args[]) throws Exception
	{
		String line;
		BufferedReader stdin = 
            new BufferedReader(
                new InputStreamReader(System.in));
 
        StringTokenizer st;
        int num;
        while(true)
        {
        	line=stdin.readLine();
        	st = new StringTokenizer(line);
        	num = Integer.parseInt(st.nextToken());
        	if(prime(num)==true)
        		System.out.println(num+" is Prime!");
        	else
        		System.out.println(num+" is not Prime!");
        }
	}
}