只接受 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（$0.05、$0.10、$0.20、$0.50、$1.00、$2.00、$5.00、$10.00、$20.00、$50.00、$100.00）并输出任何余数的代码，输出代码类似于：

    .00 remains to be paid. Insert money: .00
    You gave .00.
    .00 remains to be paid. Insert money: 3
    Invalid value. Try again.
    .00 remains to be paid. Insert money: 
    Invalid value. Try again.
    .00 remains to be paid. Insert money: .00
    You gave .00
    .00 remains to be paid. Insert money: .00
    Invalid value. Try again.

不幸的是，目前，当我输入像“3”这样的整数时，它有时会输出 "empty string"，有时会输出 "Invalid value. Try again."，但仍然将整数的值作为 paidTotal 的一部分，即

    .00 remains to be paid. Insert money: .00
    You gave .00.
    .00 remains to be paid. Insert money: 4
    empty String
    .00 remains to be paid. Insert money: .00
    You gave .00.
    .00 remains to be paid. Insert money: 9
    empty String
    .00 remains to be paid. Insert money: 9
    Invalid value. Try again.
    .00 remains to be paid. Insert money: .00
    You gave .00.
    .00 remains to be paid. Insert money: .00
    You gave .00
    .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("[=13=].05", "[=13=].10", "[=13=].20", "[=13=].50", ".00", ".00", ".00", ".00", ".00", ".00", "0.00");

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

您有时会看到 "Empty String" 的原因是，对于某些输入，您没有包括美元符号。所以 String noDollar = moneyEntered.substring(1); 跳过唯一的字符，然后你有空字符串。 "Invalid value. Try again." 当包含美元符号但货币值不在 ArrayList 中时正确出现。

在验证 validMoney 包含 moneyEntered 之前，您还将 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，您再次将 moneyAsDouble 添加到 paidTotal。

我认为这里有多个问题可以解决。逐步浏览代码，看看它做了什么。您会看到订单失败的地方。

Answer 2

我建议将输入视为数字。在这种情况下，您可以（大量）简化验证和输入处理。

显示 Empty String 是因为有时您在键入值时不包括美元符号，并且因为 .substring(1) returns 是一个子字符串开头的字符串对于指定索引处的字符，在您的情况下 1，它会跳过一个且仅一个字符。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();
}

只接受 Java 中的有效输入并输出余数

Only accepting valid inputs in Java and outputting remainder

java

arrays

double

if-statement

while-loop