Question

我正在研究这种简单的货币转换器，只是为了强化我学到的一些概念。一切都按计划工作，除非转换器第一次运行，while循环的第二次迭代导致第一个答案同时使用if和else。输出如下：

将美元转换为哪种货币？ [日元，元，比索，英镑，欧元] 磅

您想转换多少美元？ 5

您已将$ 5.0转换为3.8磅

将美元转换为哪种货币？ [日元，元，比索，英镑，欧元] 请选择一种货币将美元转换成哪种货币？ [Yen，Yuan，Peso，Pound，Euro]

货币类：

package currency;

import java.util.HashMap;
import java.util.Map;

public class Currency {

    private Map<String, Double> ct;
    private double newCurrency;
    private String answer;
    private double amount;

    public Currency() {
        this.ct = new HashMap<String, Double>();
    }

    // Getters and Setters
    public void setAnswer(String answer) {
        this.answer = answer;
    }

    public String getAnswer() {
        return this.answer;
    }

    public void setAmount(double amount) {
        this.amount = amount;
    }

    public double getAmount() {
        return this.amount;
    }

    // Current available currencies
    public void loadMap() {
        ct.put("Pound", 0.76);
        ct.put("Euro", 0.85);
        ct.put("Yen", 112.23);
        ct.put("Yuan", 6.61);
        ct.put("Peso", 18.87);

        System.out.println(ct.keySet());

    }

    // Multiples amount times currency
    public double multiplyCurrency(String answer, double amount) {

        newCurrency += ct.get(getAnswer()) * getAmount();

        return newCurrency;

    }

    public double getNewCurrency() {
        return this.newCurrency;
    }

    // Checks user if Map contains userinput.
    public boolean checkAnswer(String answer) {
        if (!ct.containsKey(answer)) {
            return false;
        } else {
            return true;
        }
    }


    @Override
    public String toString() {
        return "You have converted $" + getAmount() + " into " + getNewCurrency() + " " + this.answer + "\n";
    }

}

逻辑课程：

package logic;

import java.util.Scanner;

import currency.Currency;

public class Logic {

    private Currency currency;
    private Scanner reader;
    private boolean running;
    private String answer;

    public Logic() {
        this.currency = new Currency();
        this.reader = new Scanner(System.in);
        this.running = true;
        this.answer = null;
    }

    public void start() {

        //Runs until quit
        while (running) {
            System.out.println("Convert US dollar into which currency?");
            currency.loadMap();
            answer = reader.nextLine();
            currency.setAnswer(answer);

            // checks to make sure the value is in the map
            if (currency.checkAnswer(currency.getAnswer()) == true) {
                System.out.println("\n" + "How many dollars would you like converted?");
                double amount = reader.nextDouble();
                currency.setAmount(amount);
                currency.multiplyCurrency(currency.getAnswer(), currency.getAmount());
                System.out.println("");
                System.out.println(currency);

            } else {
                System.out.println("Please select a currency");
            }

        }
    }
}

主类：

package logic;

public class Main {

    public static void main(String[] args) {

        Logic l = new Logic();

        l.start();


    }

}

我真的很感激任何反馈，所以我可以记录，并且永远不会再发生这种情况。提前谢谢。

Answer 1

在Currency课程中，只需将answer = reader.nextLine();更改为answer = reader.next();

即可

归因于this - 即在nextDouble();

上引起新行

另外，请注意，如果用户未输入货币的确切文本，则只会打印else语句并重新开始。

Answer 2

Scanner.nextDouble方法不会消耗输入的最后一个换行符，因此在下一次调用Scanner.nextLine时会消耗换行符。你基本上遇到了与this post

中提到的相同的问题

一个简单的解决方法是将值读取为String并将其解析为double，以便替换

double amount = reader.nextDouble();

通过

double amount = Double.parseDouble(reader.nextLine());

If和Else语句在while循环的第二次迭代中运行

2 个答案: