仅接受 Java 中的有效输入并输出余数

Question

我正在尝试编写接受有效输入的代码（0.05 美元、0.10 美元、0.20 美元、0.50 美元、1.00 美元、2.00 美元、5.00 美元、10.00 美元、20.00 美元、50.00 美元、100.00 美元）并输出任何余数，输出代码类似于：

    $38.00 remains to be paid. Insert money: $20.00
    You gave $20.00.
    $18.00 remains to be paid. Insert money: 3
    Invalid value. Try again.
    $18.00 remains to be paid. Insert money: $9
    Invalid value. Try again.
    $18.00 remains to be paid. Insert money: $10.00
    You gave $30.00
    $8.00 remains to be paid. Insert money: $8.00
    Invalid value. Try again.

不幸的是，当我输入像'3'这样的整数时，它有时会输出“空字符串”，有时会输出“无效值。再试一次。”但仍将整数的值作为paidTotal 的一部分，即

    $18.00 remains to be paid. Insert money: $10.00
    You gave $10.00.
    $8.00 remains to be paid. Insert money: 4
    empty String
    $8.00 remains to be paid. Insert money: $2.00
    You gave $10.00.
    $8.00 remains to be paid. Insert money: 9
    empty String
    $8.00 remains to be paid. Insert money: 9
    Invalid value. Try again.
    $8.00 remains to be paid. Insert money: $5.00
    You gave $10.00.
    $8.00 remains to be paid. Insert money: $2.00
    You gave $12.00
    $6.00 remains to be paid. Insert money:

这是我的代码的相关部分。任何帮助将不胜感激！

System.out.print("$" + formatter.format(priceSum) + " remains to be paid. Insert money: ");
String moneyEntered = keyboard.nextLine();
System.out.println("");
String noDollar = moneyEntered.substring(1);
double moneyAsDouble = Double.parseDouble(noDollar);
double paidTotal = 0;
paidTotal += moneyAsDouble;
List validMoney = Arrays.asList("$0.05", "$0.10", "$0.20", "$0.50", "$1.00", "$2.00", "$5.00", "$10.00", "$20.00", "$50.00", "$100.00");

boolean moneyEnteredFound = true;

while(true) {
    if (validMoney.contains(moneyEntered)) {
        while (paidTotal < priceSum) {
            if (validMoney.contains(moneyEntered)) {
                System.out.println("You gave $" + formatter.format(paidTotal));
                System.out.print("$" + formatter.format(priceSum - paidTotal) + " remains to be paid. Enter coin or note: ");
                moneyEntered = keyboard.nextLine();
                noDollar = moneyEntered.substring(1);
                moneyAsDouble = Double.parseDouble(noDollar);
                        paidTotal += moneyAsDouble;
            } else {
                System.out.println("Invalid value. Try again.");
                System.out.print("$" + formatter.format(priceSum - paidTotal) + " remains to be paid. Enter coin or note: ");
                moneyEntered = keyboard.nextLine();
            }
         }
       }
    }

Answer 1

我建议将输入视为数字。在这种情况下，您可以（很多）简化验证，并且通常简化输入处理。

之所以会显示 Empty String 是因为有时您在键入值时不包含美元符号，并且因为 .substring(1) 返回的字符串是以指定索引处的字符开头的子字符串，在您的case 1，它会跳过那个且只有一个字符。此外，您还有一些其他细节需要注意……我对您的代码进行了一些重构，希望对您有所帮助:)

final Set<Double> VALID_INPUT = new HashSet<>(Arrays.asList(0.05, 0.10, 0.20, 0.50, 1.00,
    2.00, 5.00, 10.00, 20.00, 50.00, 100.00));
final Scanner scanner = new Scanner(System.in);
//final double priceSum = 104.89d; // This should be a parameter or an input
double acc = 0.00d;

System.out.printf("$%.2f remains to be paid. Insert money: $", priceSum);

String input = scanner.nextLine();

while (acc < priceSum) {
  final Double amount = Double.valueOf(input); // TODO: Handle invalid format here

  // Uncomment the second one to avoid negative values (if not allowed)
  if (VALID_INPUT.contains(value)/* && (acc + amount < priceSum)*/) {
    acc += value;
    System.out.printf("You gave $%.2f%n", value);
  } else {
    System.out.println("Invalid value. Try again...");
  }
  System.out.printf("$%.2f remains to be paid. Enter coin or note: $", priceSum - acc);
  input = scanner.nextLine();
}

Answer 2

您有时会看到“空字符串”的原因是对于某些输入，您不包括美元符号。所以String noDollar = moneyEntered.substring(1); 跳过了唯一一个字符，然后你就有了空字符串。 “无效值。再试一次。”当包含美元符号但货币值不在ArrayList 中时正确发生。

在验证 validMoney 包含 moneyEntered 之前，您还要将 moneyAsDouble 添加到 paidTotal。因此，无论输入是否有效，double 值都将添加到paidTotal。此外，在 while 循环中，您将 moneyAsDouble 再次添加到 paidTotal。

我认为这里有多个问题可以解决。一步一步地浏览代码，看看它做了什么。您将看到您的订单失败的地方。