如何在 Java 中正确返回金钱双变量

Question

我目前正在为学校做一个作业，我需要编写一个程序，它需要在这种模式下返回你的更改

输入： 购买金额：$12.45 给定金额：$15.00

输出： 零钱：2.55 美元 2张一美元的钞票 2个季度 1 镍

但是，如果我处理这种情况，它工作得很好。现在，如果我想让这个场景发挥作用，我会得到 ​​p>

输入： 购买金额：$19.51 给定金额：$50.01

输出：

二十美元钞票 1 十元钞票：1 宿舍：1 硬币：2 便士：4

这是不正确的，因为我要返回客户 30.49 而不是 30.5

不知道这里有什么问题。

谢谢

 boolean isFiveBillOn = false, isTwentybillOn = false, isTenbillOn = false, isDollarOn = false, isQuartersOn = false, isDimesOn = false, isNicklesOn = false, isPenniesOn = false;

    //retrieve amount due
    String moneyd = JOptionPane.showInputDialog("Enter the amount due");
    double amountd = Double.parseDouble(moneyd);

    String moneyr = JOptionPane.showInputDialog("Enter amount you would like to pay");
    double amountr = Double.parseDouble(moneyr);

    //calculate difference
    double difference = (amountr - amountd);

    //convert to pennies
    int balance = (int)(difference * 100);

    //twenty dollar bill
    int twentydollars = balance / 2000;
    balance = (balance % 2000);
    if (twentydollars > 0) {
        isTwentybillOn = true;
    }

    //ten dollar bill
    int tendollars = balance / 1000;
    balance = (balance % 1000);
    if (tendollars > 0) {
        isTenbillOn = true;
    }

    //five dollar bill
    int fivedollars = balance / 500;
    balance = (balance % 500);
    if (fivedollars > 0) {
        isFiveBillOn = true;
    }

    //dollar bill
    int dollars = balance / 100;
    balance = (balance % 100);
    if (dollars > 0) {
        isDollarOn = true;
    }

    //quartes
    int quarters = balance / 25;
    balance = (balance % 25);
    if (quarters > 0) {
        isQuartersOn = true;
    }

    //dimes
    int dimes = balance / 10;
    balance = (balance % 10);
    if (dimes > 0) {
        isDimesOn = true;
    }

    //nickles
    int nickles = balance / 5;
    balance = (balance % 5);
    if (nickles > 0){
        isNicklesOn = true;
    }

    //pennies
    int pennies = balance / 1;
    balance = (balance % 1);
    if (pennies > 0){
        isPenniesOn = true;
    }

    //checking for difference over 0
    if (difference < 0) {
        JOptionPane.showMessageDialog(null, "The amount received can't be less than the amount owned");
    } else {
        // Returning Message
        } if (isTwentybillOn) {
                    System.out.println("Twenty dollar bill " + twentydollars);
        } if (isTenbillOn) {
                    System.out.println("Ten dollar bill: " + tendollars);
        } if (isDollarOn) {
                    System.out.println("One Dollar Bill: " + dollars);
        } if (isQuartersOn) {
                    System.out.println("Quarters: " + quarters);
        } if (isDimesOn) {
                    System.out.println("Dimes: " + dimes);
        } if (isNicklesOn) {
                    System.out.println("Nickles: " + nickles);
        } if (isPenniesOn) {
                    System.out.println("Pennies: " + pennies);
        } else {
            System.out.println("Thanks! have a good day");
        }
    }

Answer 1

您不应该使用double 或任何其他浮点数据类型来表示货币。原因是它们不能准确地表示所有值。例如，以下行：

System.out.println(new BigDecimal(0.1));

打印

0.1000000000000000055511151231257827021181583404541015625

如需详细解释原因，请参阅What Every Computer Scientist Should Know About Floating-Point Arithmetic。

我建议改用BigDecimal。

如果您只想使用原语，另一种方法是使用 int 来存储以美分为单位的货币值，并在显示值时除以 100。