Math

数学相关的工具类，提供大量的静态方法，完成与数学运算的相关操作。

常用方法

public static double abs(double num);绝对值

public static double ceil(double num);向上取整

public static double floor(double num);向下取整

public static long round(double num);四舍五入

小问题举例

1、计算在-10.8到5.9之间，绝对值大于6或者小于2.1的整数有多少个？

import java.util.ArrayList;
import static java.lang.Math.ceil;
import static java.lang.Math.floor;
import static java.lang.Math.abs;

public class Demo1 {
    //计算在-10.8到5.9之间，绝对值大于6或者小于2.1的整数有多少个？
    public static void main(String[] args) {
        double a=-10.8;
        double b=5.9;
        //分别向上向下取整数并且强制转换为整数
        int c=(int)ceil(a);
        int d=(int)floor(b);
        ArrayList<Integer> list=new ArrayList<>();
        int count=0;
        for (int i = c; i <= d ; i++) {
            if(abs(i)>6||abs(i)<2.1) {
                list.add(i);
                count++;
            }
        }
        System.out.println("绝对值大于6或者小于2.1的整数:"+list+",个数为："+count);
    }
}

2、发红包的小例子

群主有一笔金额，群主从余额中扣除金额，将金额均分为n份，让成员领取。

成员领取红包后，保存到成员的余额当中。

public class User {
    private String name;
    private int balance;

    public User() {
    }

    public User(String name, int balance) {
        this.name = name;
        this.balance = balance;
    }
    public void show(){
        System.out.println(name+":"+balance);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getBalance() {
        return balance;
    }

    public void setBalance(int balance) {
        this.balance = balance;
    }
}

import java.util.ArrayList;

public class GroupHolder extends User{
    public GroupHolder() {
    }

    public GroupHolder(String name, int balance) {
        super(name, balance);
    }

    public ArrayList<Integer> send (int totalMoney, int count){
        //判断余额是否充足
        if(super.getBalance()<totalMoney){
            System.out.println("余额不足！");
        }else {
            //设置剩余红包钱数
            super.setBalance(super.getBalance()-totalMoney);
        }

        int redbag=totalMoney/count;
        int redbag1=totalMoney%count;
        ArrayList<Integer> list=new ArrayList<>();
        for (int i = 0; i < count-1; i++) {
            list.add(redbag);
        }
        list.add(redbag+redbag1);
        return list;
    }

}

import java.util.Random;

public class NormalUser extends User{
    public NormalUser() {
    }

    public NormalUser(String name, int balance) {
        super(name, balance);
    }

    public void receive(ArrayList<Integer> list){
        //从群主的红包中随机抽取一个
        Random r=new Random();
        int num=r.nextInt(list.size());
        //获取指定位置的红包,并加入余额当中
        super.setBalance(super.getBalance()+list.get(num));
        //获取红包后将红包移除
        list.remove(num);

    }
}

import java.util.ArrayList;

public class Aplication {

    public static void main(String[] args) {
        ArrayList<Integer> list =new ArrayList<>();
        GroupHolder g=new GroupHolder("群主",1000);
        NormalUser n1=new NormalUser("张三",10);
        NormalUser n2=new NormalUser("李四",10);
        NormalUser n3=new NormalUser("王五",10);
        g.show();
        n1.show();
        n2.show();
        n3.show();
        System.out.println("===========");
        list=g.send(20,3);
        n1.receive(list);
        n2.receive(list);
        n3.receive(list);
        g.show();
        n1.show();
        n2.show();
        n3.show();
    }
}