黑马JAVA P80 String案例：验证码、登录、隐私号码

package com.itheima.string;

import java.util.Random;

public class StringExec8 {
    

    public static void main(String[] args) {
        //1.定义出现的字符信息
        String datas = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

        //2.循环5次，每次生成一个随机的索引，提取对应的字符连接起来即可
        String code = "";
        Random  r = new Random();
        for (int i = 0; i < 5; i++) {
            //随机一个索引
            int index = r.nextInt(datas.length());
            char c = datas.charAt(index);
            code += c;
        }

        //3.输出字符串变量即可
        System.out.println(code);


    }
}

package com.itheima.string;

import java.util.Scanner;



public class StringExec7 {
    public static void main(String[] args) {
        //1.定义正确的登录名称和密码
        String okLoginName = "admin";
        String okPassword = "itheima" ;

        //2.定义一个循环，循环3次，让用户登录
        Scanner sc = new Scanner(System.in);
        for (int i = 0; i <= 3 ; i++) {
            System.out.println("请您输入登录名称：");
            String loginName = sc.next();
            System.out.println("请您输入登录密码：");
            String password = sc.next();

            //3.判断登录是否成功
            if(okLoginName.equals(loginName)){
                //4.判断密码是否正确
                if(okPassword.equals(password)){
                    System.out.println("登录成功！欢迎进入系统随意浏览~~~");
                    break;
                }else{
                    // 密码错误了
                    System.out.println("您的密码不正确！您还剩余" + (3 - i) + "次机会登录！");
                }
            }else{
                System.out.println("您的登录名称不正确！您还剩余" + (3 - i) + "次机会登录！");
            }

        }
    }
}

package com.itheima.string;

import java.util.Scanner;



public class StringExce8 {
    public static void main(String[] args) {
        //1.键盘录入一个手机号码
        Scanner sc = new Scanner(System.in);
        System.out.println("请您输入您的手机号码：");
        String tel = sc.next();

        //2.截取号码的前三位，后四位    18665666520
        String before = tel.substring(0,3);   // 0  1  2
        String after = tel.substring(7);   // 从索引7开始截取到手机号码的末尾

        String s = before + "****" + after;
        System.out.println(s);

    }
}