Java - 不能接受便士的自动售货机

Question

所以我正在开发一个 java 项目，该项目涉及创建一个根据温度调整价格的汽水机。我似乎不知道如何确保机器在接受用户付款时不接受便士。

我觉得我编码过度了，但我已经无计可施了，因为我不知道如何不接受便士。

import java.util.*;
import java.text.*;
public class SodaMachine extends SodaTester
{
    public static void main(String[] args)
    {
        double temp;
        double money;
        double change;
        double price1 = .50;
        double price2 = .55;
        double price3 = .60;
        double price4 = .65;
        double price5 = .75;
        double price6 = .80;
        double price7 = .85;
        double price8 = .90;
        double price9 = 1.00;

        System.out.println("Hi there! Please enter the temperature in Farenheit:");
        Scanner scan = new Scanner(System.in);
        temp = scan.nextDouble();
        DecimalFormat fmt = new DecimalFormat("0.#");

        NumberFormat fmt2 = NumberFormat.getCurrencyInstance();

        if (temp < 40 || temp > 120)
        {
            System.out.println("Invalid input. Temperature should be between 40 and 120 degrees Farenheit.");
            while (temp < 40 || temp > 120)
            {
                temp = scan.nextDouble();
                System.out.println("The rounded temperature in degrees Farenheit is: " + fmt.format(temp));
                System.out.println("Invalid input. Temperature should be between 40 and 120 degrees Farenheit.");
            }
        }

        if(temp < 50 && temp >= 40)
        {
            System.out.println("The rounded temperature in degrees Farenheit is: " + fmt.format(temp));
            System.out.println("The price is: " + fmt2.format(price1));

            System.out.println("Please insert amount of payment: ");
            money = scan.nextDouble();
            while (money < price1)
            {
                System.out.println("Invalid input please try again. Your total is: " + fmt2.format(price1));
                money = scan.nextDouble();
            }
            change = money - price1;
            System.out.println("Your Change is: " + fmt2.format(change));
        }else if (temp >= 50 && temp <= 60) {
            System.out.println("The rounded temperature in degrees Farenheit is: " + fmt.format(temp));
            System.out.println("The price is: " + fmt2.format(price2));

            System.out.println("Please insert amount of payment: ");
            money = scan.nextDouble();
            while (money < price2)
            {
                System.out.println("Invalid input please try again. Your total is: " + fmt2.format(price2));
                money = scan.nextDouble();
            }
            change = money - price2;
            System.out.println("Your Change is: " + fmt2.format(change));
        }else if (temp > 60 && temp <= 65) { 
            System.out.println("The rounded temperature in degrees Farenheit is: " + fmt.format(temp));
            System.out.println("The price is: " + fmt2.format(price3));

            System.out.println("Please insert amount of payment: ");
            money = scan.nextDouble();
            while (money < price3)
            {
                System.out.println("Invalid input please try again. Your total is: " + fmt2.format(price3));
                money = scan.nextDouble();
            }
            change = money - price3;
            System.out.println("Your Change is: " + fmt2.format(change));
        }else if (temp > 65 && temp <= 70) {
            System.out.println("The rounded temperature in degrees Farenheit is: " + fmt.format(temp));
            System.out.println("The price is: " + fmt2.format(price4));

            System.out.println("Please insert amount of payment: ");
            money = scan.nextDouble();
            while (money < price4)
            {
                System.out.println("Invalid input please try again. Your total is: " + fmt2.format(price4));
                money = scan.nextDouble();
            }
            change = money - price4;
            System.out.println("Your Change is: " + fmt2.format(change));
        }else if (temp > 70 && temp <= 75) {
            System.out.println("The rounded temperature in degrees Farenheit is: " + fmt.format(temp));
            System.out.println("The price is: " + fmt2.format(price5));

            System.out.println("Please insert amount of payment: ");
            money = scan.nextDouble();
            while (money < price5)
            {
                System.out.println("Invalid input please try again. Your total is: " + fmt2.format(price5));
                money = scan.nextDouble();
            }
            change = money - price5;
            System.out.println("Your Change is: " + fmt2.format(change));
        }else if (temp > 75 && temp <= 80) {
            System.out.println("The rounded temperature in degrees Farenheit is: " + fmt.format(temp));
            System.out.println("The price is: " + fmt2.format(price6));

            System.out.println("Please insert amount of payment: ");
            money = scan.nextDouble();
            while (money < price6)
            {
                System.out.println("Invalid input please try again. Your total is: " + fmt2.format(price6));
                money = scan.nextDouble();
            }
            change = money - price6;
            System.out.println("Your Change is: " + fmt2.format(change));
        }else if (temp > 80 && temp <= 85) {
            System.out.println("The rounded temperature in degrees Farenheit is: " + fmt.format(temp));
            System.out.println("The price is: " + fmt2.format(price7));

            System.out.println("Please insert amount of payment: ");
            money = scan.nextDouble();
            while (money < price7)
            {
                System.out.println("Invalid input please try again. Your total is: " + fmt2.format(price7));
                money = scan.nextDouble();
            }
            change = money - price7;
            System.out.println("Your Change is: " + fmt2.format(change));
        }else if (temp > 85 && temp <= 90) {
            System.out.println("The rounded temperature in degrees Farenheit is: " + fmt.format(temp));
            System.out.println("The price is: " + fmt2.format(price8));

             System.out.println("Please insert amount of payment: ");
            money = scan.nextDouble();
            while (money < price8)
            {
                System.out.println("Invalid input please try again. Your total is: " + fmt2.format(price8));
                money = scan.nextDouble();
            }
            change = money - price8;
            System.out.println("Your Change is: " + fmt2.format(change));
        }else if (temp > 90 && temp <= 120) {
            System.out.println("The rounded temperature in degrees Farenheit is: " + fmt.format(temp));
            System.out.println("The price is: " + fmt2.format(price9));

            System.out.println("Please insert amount of payment: ");
            money = scan.nextDouble();
            while (money < price9)
            {
                System.out.println("Invalid input please try again. Your total is: " + fmt2.format(price9));
                money = scan.nextDouble();
            }
            change = money - price9;
            System.out.println("Your Change is: " + fmt2.format(change));
        }
    }






















}

Answer 1

我不会详细介绍您当前的代码，但您基本上想检查从用户处读取的十进制值模 0.05 是否等于 0 (所以没有余数)。其中的一个问题是，当您使用 double 时，浮点精度可能会干扰检查，这就是为什么您总是希望使用 java.math.BigDecimal 来表示货币计算。

这里是一个例子:

BigDecimal input = new BigDecimal(scanner.next());
if(input.remainder(new BigDecimal("0.05")).compareTo(BigDecimal.ZERO) == 0){
  System.out.println("Input "+input+" is valid!");
} else{
  System.out.println("Input "+input+" is not valid!");
}

对于输入"1"、"1.00"、"1.05"、"4.35"， "1.01"、"3.21"、"4.68" 它将输出以下内容:

Input 1 is valid!
Input 1.00 is valid!
Input 1.05 is valid!
Input 4.35 is valid!
Input 1.01 is not valid!
Input 3.21 is not valid!
Input 4.68 is not valid!

Try it online.

<小时/>

由于 BigDecimal 对于 Java 新用户来说可能会很困惑，您也许可以让用户输入以分为单位的金额(整数)，在这种情况下，它可以是这样的:

int input = scanner.nextInt();
if(input % 5 == 0){
  System.out.println("Input "+input+" is valid!");
} else{
  System.out.println("Input "+input+" is not valid!");
}

对于输入“100”、“105”、“435”、“101”、 “321”，“468”它将输出以下内容:

Input 100 is valid!
Input 105 is valid!
Input 435 is valid!
Input 101 is not valid!
Input 321 is not valid!
Input 468 is not valid!

Try it online.

<小时/>

编辑:由于我有一些时间，我用可重用的方法重新设计了您的解决方案。

请仔细看看我做了什么，如果您对特定部分有任何疑问，请告诉我。它现在使用递归方法，直到用户输入有效的输入。方法中的 boolean showMessage 参数仅显示一次“请输入 X” 消息。

import java.lang.IllegalArgumentException;
import java.lang.NumberFormatException;
import java.math.BigDecimal;
import java.text.NumberFormat;
import java.util.InputMismatchException;
import java.util.Scanner;
public class SodaMachine{ 
  private static final String currencySymbol = "$";
  private static final BigDecimal roundOn = new BigDecimal("0.05");
  private Scanner scanner;
  private NumberFormat currencyFormat;

  public SodaMachine(){
    scanner = new Scanner(System.in);
    currencyFormat = NumberFormat.getCurrencyInstance();
  }

  public static void main(String[] args){
    SodaMachine sodaMachine = new SodaMachine();
    double farenheitInput = sodaMachine.enterFarenheit(true);
    System.out.println("The temperature in degrees Farenheit you've entered is: " + farenheitInput);

    BigDecimal price = sodaMachine.determinePrice(farenheitInput);
    System.out.println("The price is: " + sodaMachine.currencyFormat.format(price));

    BigDecimal payment = sodaMachine.enterPayment(price, true);

    BigDecimal change = payment.subtract(price);
    System.out.println("Your change is: " + sodaMachine.currencyFormat.format(change));
  }

  private double enterFarenheit(boolean showMessage){
    if(showMessage){
      System.out.println("Hi there! Please enter the temperature in Farenheit:");
    }

    double farenheitInput;
    try{
      farenheitInput = scanner.nextDouble();
    } catch(InputMismatchException ex){
      scanner.nextLine(); // Get rid of the invalid user-input
      System.out.println("The value you've entered is not a valid. The input should be a decimal input. Please try again.");
      return enterFarenheit(false);
    }

    if(farenheitInput < 40 | farenheitInput > 120){
      System.out.println("Invalid input. Temperature should be between 40 and 120 degrees Farenheit.");
      return enterFarenheit(false);
    }

    return farenheitInput;
  }

  private BigDecimal determinePrice(double farenheit){
    String strPrice;
    // Temperature is in the range [40, 50):
    if(farenheit >= 40 && farenheit < 50){
      strPrice = "0.50";
    }
    // Temperature is in the range [50, 60]:
    else if(farenheit >= 50 && farenheit <=60){
      strPrice = "0.55";
    }
    // Temperature is in the range (60, 65]:
    else if(farenheit > 60 && farenheit <= 65){
      strPrice = "0.60";
    }
    // Temperature is in the range (65, 70]:
    else if(farenheit > 65 && farenheit <= 70){
      strPrice = "0.65";
    }
    // Temperature is in the range (70, 75]:
    else if(farenheit > 70 && farenheit <= 75){
      strPrice = "0.75";
    }
    // Temperature is in the range (75, 80]:
    else if(farenheit > 75 && farenheit <= 80){
      strPrice = "0.80";
    }
    // Temperature is in the range (80, 85]:
    else if(farenheit > 80 && farenheit <= 85){
      strPrice = "0.85";
    }
    // Temperature is in the range (85, 90]:
    else if(farenheit > 85 && farenheit <= 90){
      strPrice = "0.90";
    }
    // Temperature is in the range (90, 120]:
    else if(farenheit > 90 && farenheit <= 120){
      strPrice = "1.00";
    }
    // Invalid temperature range:
    else{
      // Since we already validated the input-range, it should never go here,
      // but added it just in case.
      throw new IllegalArgumentException("The temperature must be in the range [40, 120]!");
    }
    return new BigDecimal(strPrice);
  }

  private BigDecimal enterPayment(BigDecimal price, boolean showMessage){
    if(showMessage){
      System.out.println("Please enter amount of payment: ");
    }

    String userInput = scanner.next();
    // Remove the optional currency symbol from the user input
    userInput = userInput.replace(currencySymbol, "");

    BigDecimal paymentInput;
    try{
      paymentInput = new BigDecimal(userInput);
    } catch(NumberFormatException ex){
      scanner.nextLine(); // Get rid of the invalid user-input
      System.out.println("The value you've entered is not a valid. The input should be a price input. Please try again.");
      return enterPayment(price, false);
    }

    if(paymentInput.compareTo(price) < 0){
      System.out.println("Your payment of " + currencyFormat.format(paymentInput) + " is too low. Please try again. The total price is: " + currencyFormat.format(price));
      return enterPayment(price, false);
    }

    if(paymentInput.remainder(roundOn).compareTo(BigDecimal.ZERO) != 0){
      System.out.println("Your payment should be rounded to " + currencyFormat.format(roundOn) + ". Please try again.");
      return enterPayment(price, false);
    }

    return paymentInput;
  }
}

Try it online.