数组、随机数、时间、字符串在购物系统中的应用

1．用数组实现存放多个用户名和密码

//定义一个字符串数组变量存放各个用户名
import java.util.Scanner;//导入一个外部的java类
String [] usernames = new String[10];
usernames[0] = "admin1";
usernames[1] = "admin2";
usernames[2] = "admin3";
usernames[3] = "admin4";
usernames[4] = "admin5";
usernames[5] = "admin6";
usernames[6] = "admin7";
usernames[7] = "admin8";
usernames[8] = "admin9";
usernames[9] = "admin10";

String [] passwords = new String[10];
passwords[0] = "1111";
passwords[1] = "2222";
passwords[2] = "3333";
passwords[3] = "4444";
passwords[4] = "5555";
passwords[5] = "6666";
passwords[6] = "7777";
passwords[7] = "8888";
passwords[8] = "9999";
passwords[9] = "0000";
while(true) {
Scanner input = new Scanner(System.in);
System.out.println("请输入用户名：");
String name = input.next();
System.out.println("请输入密码：");
String pass = input.next();

for(int i = 0; i < usernames.length; i ++) {
if(name.equals(usernames[i]) && pass.equals(passwords[i])) {
System.out.println("登录成功");
System.exit(1);
}
}

System.out.println("登录失败");
}

2.用java.util.Random;实现幸运抽奖

import java.util.Random;//产生随机数的外部java类
Random rand = new Random();
int randNum = rand.nextInt(5) + 1;//随机产生一整数clientNum,(1 <= clientNum <= 5)
int clientNum = 0;
String clientName = null;
String clientBirthday = null;
int clientIntegral = 0;//客户积分
switch(randNum){
case 1:
clientNum = 1001;
clientName = "张三";
clientBirthday = "1992-01-01";
clientIntegral = 2000;
break;
case 2:
clientNum = 1002;
clientName = "李四";
clientBirthday = "1991-08-02";
clientIntegral = 2000;
break;
case 3:
clientNum = 1003;
clientName = "王五";
clientBirthday = "1993-06-22";
clientIntegral = 2000;
break;
case 4:
clientNum = 1004;
clientName = "赵六";
clientBirthday = "1996-04-10";
clientIntegral = 2000;
break;
case 5:
clientNum = 1005;
clientName = "陈七";
clientBirthday = "1995-12-03";
clientIntegral = 2000;
break;
}
System.out.println("幸运的客户是：" + clientName);
System.out.println("客户编号\t\t客户姓名\t\t客户生日\t\t客户积分\n");
System.out.println(clientNum + "\t\t" + clientName +"\t\t" + clientBirthday + "\t\t" + clientIntegral +"\n");
System.out.println("恭喜以上客户，获得价值￥18的黑人牙膏一支");
System.out.println("请按任意键继续！");
String arbi = input.next();
if(arbi != "\r"){
continue;
}

3.用java.util.Calendar;java.text.SimpleDateFormat;和substring()方法实现当天是否是某客户的生日的判断

import java.util.Scanner;
import java.util.Calendar;//导入一个外部的java类
import java.text.SimpleDateFormat;
Calendar d = Calendar.getInstance();//获取当天的日期
SimpleDateFormat date = new SimpleDateFormat("MM-dd");
String mmdd = date.format(d.getTime());//当天的日期，按MM-dd格式输出
String clientName = "赵六";
String clientBirthday = "1996-04-10";
String md = clientBirthday.substring(5,clientBirthday.length());//MM-dd格式的生日
if(md.equals(mmdd)){
System.out.println("今天是" + clientName + "的生日！生日快乐！");
System.out.println("请按任意键继续！");
String arbi = input.next();
if(arbi != "\r"){
continue;
}
}else{
System.out.println("对不起，今天没有过生日的用户");
System.out.println("请按任意键继续！");
String arbi = input.next();
if(arbi != "\r"){
continue;
}
}