Java中货币找零计算的浮点数精度问题及解决方案

import java.util.Scanner;

public class CashProblem {
    public static void main(String[] args){
        Scanner scanner_obj = new Scanner(System.in);

        System.out.print("Enter Amount: $");
        double amount = Double.parseDouble(scanner_obj.nextLine());
        double[] change = calc_Change(amount);

        System.out.println(change[0] + " Quarters");
        System.out.println(change[1] + " Dimes");
        System.out.println(change[2] + " Nickels");
        System.out.println(change[3] + " Pennies");

        System.out.println(check_Change(amount, change));
    }

    public static double[] calc_Change(double amount){
        double[] change = {0, 0, 0, 0};
        // 尝试通过循环减去硬币面值
        while (amount >= 0.25){amount -= 0.25; change[0] += 1;}
        while (amount >= 0.10){amount -= 0.10; change[1] += 1;}
        while (amount >= 0.05){amount -= 0.05; change[2] += 1;}
        while (amount >= 0.01){amount -= 0.01; change[3] += 1;}

        return change;
    }

    public static boolean check_Change(double amount, double[] change){
        double total = change[0]*0.25 + change[1]*0.10 + change[2]*0.05 + change[3]*0.01;
        System.out.println("原始金额: " + amount + " vs 计算总和: " + total);
        return (amount == total); // 浮点数比较也存在问题
    }
}

import java.util.Scanner;

public class CashCorrected {

    public static void main(String[] args){
        Scanner scanner_obj = new Scanner(System.in);

        System.out.print("Enter Amount: $");
        double amountDouble = Double.parseDouble(scanner_obj.nextLine());
        System.out.println("输入的原始金额 (double): " + amountDouble);

        // 将美元金额转换为整数美分
        int numCents = (int) (amountDouble * 100 + 0.5); // 加0.5进行四舍五入，防止浮点数转换误差
        System.out.println("转换为整数美分: " + numCents);

        int[] change = calc_Change(numCents);

        System.out.println(change[0] + " Quarters");
        System.out.println(change[1] + " Dimes");
        System.out.println(change[2] + " Nickels");
        System.out.println(change[3] + " Pennies");

        System.out.println(check_Change(numCents, change));

        scanner_obj.close(); // 关闭Scanner
    }

    /**
     * 计算给定美分金额的找零硬币数量。
     * @param amount 待找零的美分总额。
     * @return 包含25美分、10美分、5美分、1美分硬币数量的整数数组。
     */
    public static int[] calc_Change(int amount){
        int[] change = {0, 0, 0, 0}; // 依次代表 Quarters, Dimes, Nickels, Pennies

        // 使用整数进行减法运算，避免浮点数精度问题
        while (amount >= 25){
            amount -= 25; 
            change[0] += 1;
        }
        while (amount >= 10){
            amount -= 10; 
            change[1] += 1;
        }
        while (amount >= 5){
            amount -= 5; 
            change[2] += 1;
        }
        while (amount >= 1){
            amount -= 1; 
            change[3] += 1;
        }

        return change;
    }

    /**
     * 检查计算出的硬币总值是否与原始美分金额匹配。
     * @param originalAmount 原始的美分金额。
     * @param change 计算出的硬币数量数组。
     * @return 如果总值匹配，则返回true；否则返回false。
     */
    public static boolean check_Change(int originalAmount, int[] change){
        int total = change[0]*25 + change[1]*10 + change[2]*5 + change[3]*1;
        System.out.println("原始美分: " + originalAmount + " vs 计算总和美分: " + total);
        return (originalAmount == total); // 整数比较是精确的
    }
}

Enter Amount: $0.41
输入的原始金额 (double): 0.41
转换为整数美分: 41
1 Quarters
1 Dimes
1 Nickels
1 Pennies
原始美分: 41 vs 计算总和美分: 41
true