Java类库StrringBuffer类、Math、SimpleDateFormat、Random随机数、大数字处理类和UUID 无重复数据（附带面试题）

package Example1501;
public class javaDemo {
    public static void main(String[] args) {
        StringBuffer str = new StringBuffer();
//        字符串连接
        str.append("大家好啊").append("我是电棍");
        System.out.println(str);
//        字符串反转
        str.reverse();
        System.out.println(str);
        StringBuffer str1 = new StringBuffer();
        str1.append("塔菲喵");
//        字符串插入
        str1.insert(0,"关注");
        System.out.println(str1);
        StringBuffer str3 = new StringBuffer();
        str3.append("不要断章取义");
//        字符串删除
        str3.delete(0,1);
        System.out.println(str3);
    }
}

package Example1502;
public class javaDemo {
    public static void main(String[] args) {
        CharSequence str = "千万不能断章取义啊";
//        截取字符串
        CharSequence sub = str.subSequence(3,9);
        System.out.println(sub);
    }
}

package Example1503;
public class javaDemo {
    public static void main(String[] args) {
         int i = -114514;
//        取绝对值
        System.out.println(Math.abs(i));
//        取最大值
        System.out.println(Math.max(1,112));
//        开根号
        System.out.println(Math.sqrt(4));
//        乘方
        System.out.println(Math.pow(2,2));
    }
}

package Example1504;
import java.util.Date;
public class javaDemo {
    public static void main(String[] args) {
//        获取当前时间
        Date date = new Date();
        System.out.println("有效期起始时间:"+date);
        long time  =  date.getTime();
//        时间加上10天后的毫秒数
        time+=846000*1000;
        System.out.println("有效期结束:"+new Date(time));
    }
}

package Example1505;
import java.text.SimpleDateFormat;
import java.util.Date;
public class javaDemo {
    public static void main(String[] args)throws Exception {
//        将date对象通过format函数转为str字符串
       Date date = new Date();
       SimpleDateFormat sdf = new SimpleDateFormat("yyyy-mm-dd");
       String str = sdf.format(date);
       System.out.println(str);
//       将字符串转为date对象
       String birthday = "2023-7-26";
       SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-mm-dd");
       Date date1 = sdf2.parse(birthday);
        System.out.println(date1);
    }
}

package Example1506;
import java.util.Random;
public class javaDemo {
    public static void main(String[] args) {
        Random random = new Random();
//        一个班级有62号人数那么将在62号人中抽取一个人回答问题
        System.out.println("恭喜"+random.nextInt(62)+"号，同学被抽中回答问题");
//可重复抽取的情况
         for (int  i =0;i<3;i++){
             System.out.println(random.nextInt(3));
        }
    }
}

package Example1507;
import java.util.Random;
public class javaDemo {
    public static void main(String[] args) {
        int array[] =  new int[7];
        Random random =new Random();
        int randomNumber = random.nextInt(36);
        for (int i=0;i<7;i++){
            while (isUse(randomNumber,array)){
                randomNumber = random.nextInt(36);
            }
            array[i] = randomNumber;
        }
        printArray(array);
    }
    public static boolean isUse(int data,int array[]){
        for (int i = 0;i<7;i++){
            if (array[i]==data){
                return true;
            }
        }
        return false;
    }
    public static void printArray(int array[]){
        for (int i=0;i<array.length;i++){
            System.out.println(array[i]);
        }
    }
}

package Example1508;
import java.math.BigInteger;
public class javaDemo {
    public static void main(String[] args) {
        BigInteger dead = new BigInteger("0");
//        boss血量
        BigInteger bossLife = new BigInteger("10000000000");
//        攻击力
        BigInteger attackValue = new BigInteger("5000000000");
        System.out.println("打Boss啦");
        while (bossLife.compareTo(dead)==1){
            System.out.println("勇者发动了攻击造成50000000伤害");
            bossLife = bossLife.subtract(attackValue);
            System.out.println("boss受伤了还剩余"+bossLife+"的血量");
        }
        System.out.println("大boss死了啦");
    }
}

package Example1509;
import java.util.UUID;
public class javaDemo {
    public static void main(String[] args) {
        UUID id =  UUID.randomUUID();
        System.out.println(id);
    }
}