java实用类
1、枚举
枚举是指一组固定的常量组成的类型
2、java API
java API提供了如下的常用包java.lang、java.util、java.io、java.net、java.sql
3、包装类
包装类有Byte、Boolean、Short、Character、Integer、Long、Float、Double
作业:
package com.shiyonglei; import java.util.Random; //实现随机生成9个电话号码 public class ZuoYue1 { public static void main(String[] args) { Random ran = new Random(); int num1 = 0; for(int i = 0;i<9;i++) { num1 = ran.nextInt(7)+3; int num2 = ran.nextInt(900000000)+100000000; System.out.println("1"+num1+num2); } } }
2、
package com.shiyonglei; import java.util.Random; //实现生成含有数字、大小写字母的验证码 public class ZuoYe2 { public static void main(String[] args) { Random ran1 = new Random(); for(int i = 0;i<6;i++) { int num1 = ran1.nextInt(123); if((64<num1&&num1<91)||(96<num1&&num1<123)) { char a = (char)num1; System.out.print(a); }else if(num1<10) { int b = num1; System.out.print(b); } else { i--; } } } }