没做出来啊，原来有这么多方法啊。

首先，我连质数是什么都不知道！

质数：只能被本身和1整除的数

帖子里回复了不少方法：

class Zhishu 
{
        public static void main(String[] args) 
        {
                int count=0;
                for(int i=1;i<=100;i++)
                {
                        count=0;
                        for(int j=1;j<=i;j++)
                        {
                                if(i%j==0)
                                {
                                        count++;
                                }
                        }
                        if(count==2||count==1)
                        {
                                System.out.print(i+" ");
                        }

                }
        }
}

package com.ms.test;

public class GetSushu {

        /**
         * @param args
         */
        public static void main(String[] args) {
                // TODO Auto-generated method stub
                for(int x=100;x<=999;x++){
                        boolean flag=true;
                        for(int y=2;y<x;y++){
                                if(x%y==0){
                                        flag=false;
                                        break;
                                }
                        }
                        if(flag){
                                System.out.println(x);
                        }
                        
                }
        }

}

判断某一个三位数是否是质数

import java.util.Scanner;

public class PrimeNum {

        public static void main(String[] args) {
                Scanner sc = new Scanner(System.in);
                System.out.println("请输入一个三位数");
                int  num = sc.nextInt();
                if(num<100 || num>999)
                        throw new RuntimeException("输入数据不合要求");
                
                getPrime(num);
        }
        public static void getPrime(int num){
                
                for(int x=2;x<num;x++){
                        if(num%x!=0){
                                if(x==num-1){
                                        System.out.println(num+"是质数");
                                }
                                continue;
                        }
                        else{
                                System.out.println(num+"不是质数");
                                break;
                        }                                
                }                
        }
}

列出所有介于100到你输入的三位数中的质数(不包含100)

import java.util.Scanner;

public class TotalPrimeNum {

        public static void main(String[] args) {
                Scanner sc = new Scanner(System.in);
                System.out.println("请输入一个三位数");
                int  num = sc.nextInt();
                if(num<100 || num>999)
                        throw new RuntimeException("输入数据不合要求");
                getPrime(num);
        }
        public static void getPrime(int num){
                int count = 0;//计数器记录质数个数
                W:for (int x = 101; x <= num; x++) {
                        Q:for (int y = 2; y < x; y++) {
                                if(x%y!=0){
                                        if(y==x-1){
                                                System.out.print(x+"\t");
                                                count++;
                                                continue W;
                                        }
                                        continue Q;
                                }
                                else{
                                        continue W;
                                }
                        }
                }
                System.out.println();
                System.out.println("101到"+num+"共有质数个数为："+count);        
        }
}

求三位数的质数