java产生随机数的疑惑解决方案

package cn.ffcs.ct10000.card;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Random;

public class TTEST {
    public static String getCurrStrTime(int type){
        Date date = new Date();
        DateFormat formatter = null;
        if(type == 1){
            formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        }else if(type == 2){
            formatter = new SimpleDateFormat("yyyy-MM");    //检查每月一次的业务
        }else if(type == 3){
            formatter = new SimpleDateFormat("yyyyMMddHHmmss");
        }else{
            //默认
            formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        }
        
        return formatter .format(date);
    }
    
    
    public static String getSno() {
        Random rdm = new Random();
        int i = rdm.nextInt(1000000)+1000000;
        String str = "nx" + getCurrStrTime(3) + String.valueOf(i).substring(1,7);
        return str;
            
    }
    public static void suijishu(){
        //获得一个从100000到999999之间的整数
        Random rdm = new Random();
        for(int i=0; i<1000;i++){
            int j;
            j = rdm.nextInt(1000000)+1000000;
            String str = "nx" + getCurrStrTime(3) + String.valueOf(j).substring(1,7);
            System.out.println(str);
        }
    }
    
    
    public static void t1(){
        for(int i=0;i<100;i++){
            String sno = getSno();
            if(sno.length() != 2){
                System.out.println(sno);
            }
        }        
    }
    
    public static void t2(){
        suijishu();
    }
    /**
     * @param args
     */
    public static void main(String[] args) {

//        t1();
        t2();
    }

}