基于BigDecimal、DecimalFormat、Random实现模拟红包算法

RedPacket 类

import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.Random;

public class RedPacket {
	
	
	private String sumMoney;
	
	private int count;
	private Random r = new Random();
	
	public RedPacket(String sumMoney, int count) {
		super();
		this.sumMoney = sumMoney;
		this.count = count;
	}

	public ArrayList<BigDecimal> genPacket() throws RedPacketException{
		ArrayList<BigDecimal> list = new ArrayList<>();
		BigDecimal money = new BigDecimal("0.01");
		//获取总金额的最小值
		double minMoney = money.multiply(new BigDecimal(count)).doubleValue();
		//将字符串类型的金额包装为BigDecimal
		BigDecimal totalMoney = new BigDecimal(sumMoney);
		//判断红包总金额是否大于红包最小值(判断总金额是否够分)
		if(minMoney > totalMoney.doubleValue()){
			throw new RedPacketException("每个红包不能少于0.01元");
		}
		if(minMoney == totalMoney.doubleValue()) {
			//最低金额正好等于总金额(每人0.01)
			for(int i = 0 ; i < count ; i++) {
				list.add(new BigDecimal("0.01"));
			}
			return list;
		}
		double[] scales = randomScale();
		//合计已经分配多少钱
		BigDecimal sends = new BigDecimal("0");
		for(int i = 0; i < scales.length-1 ; i++) {
			//根据比例计算每个红包的应分得的金额
			money = totalMoney.multiply(new BigDecimal(scales[i])).setScale(2, BigDecimal.ROUND_HALF_EVEN);
			sends = sends.add(money);
			list.add(money);
		}
		list.add(totalMoney.subtract(sends));
		return list;
	}
	
	public double[] randomScale() {
		//累计总随机值
		double total = 0;
		//临时数组存储每个红包的随机比例
		double[] scales = new double[count];
		for (int i = 0; i < count; i++) {
			//随机获取一个从1-100的整数
			int rint = r.nextInt(100)+1;
			scales[i] = rint;
			total += rint;
		}
		//计算比例
		for (int i = 0; i < count; i++) {
			scales[i] = scales[i] / total;
		}
		return scales;
	}
	
	public static void main(String[] args) throws RedPacketException {
		ArrayList<BigDecimal> list = new RedPacket("10", 5).genPacket();
		for (BigDecimal bd : list) {
			System.out.print(bd + "元\t");
		}
	}
}

自定义异常 RedPacketException类

public class RedPacketException extends Exception{

	public RedPacketException() {
		// TODO Auto-generated constructor stub
	}
	
	public RedPacketException(String message) {
		super(message);
	}
	
}