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--;
            }

        }
    }
}