如何将测试器返回到要求用户输入欧元/英镑/cad的开头

Question

import java.util.Scanner;
public class CurrencyTester
{ 
public static void main(String[]args)
{  

我想从一开始就循环，但不是要求用户输入相同的转换器，我怎么做呢？

    CurrencyConverter one= new CurrencyConverter();
    System.out.println("Convert dollar to euro/gbp/cad");

我想在第一个循环之后要求输入欧元英镑或cad。

    System.out.println("enter euro/gbp/cad");
    System.out.println("");
    Scanner input = new Scanner(System.in);
    String a = input.next();
    if("euro".equalsIgnoreCase(a))
    {

欧元

do { 

System.out.println("Enter Dollars:");
Scanner in = new Scanner(System.in);
String d = in.next();
if ("Q".equalsIgnoreCase(d)) {
    System.out.println("Stop!");
    break;
} else {
try {
        double ds = Double.parseDouble(d);
        one.setDollar(ds);
        System.out.println("Euro:");
        System.out.println("€"+one.getCurrencyE());
    } catch (NumberFormatException e) {
        System.out.println("Not double,wrong input");
    }
}
} while (true);

}
    if("gbp".equalsIgnoreCase(a))
    {

国内生产总值

do { System.out.println("Enter Dollars:");
Scanner in = new Scanner(System.in);
String d = in.next();
if ("Q".equalsIgnoreCase(d)) {
    System.out.println("Stop!");
    break;
} else {
    try {
        double ds = Double.parseDouble(d);
        one.setDollar(ds);
        System.out.println("GDP:");
        System.out.println("£"+one.getCurrencyG());
 } catch (NumberFormatException e) {
        System.out.println("Not double,wrong input");
 }
}
 } while (true);

}
    if("cad".equalsIgnoreCase(a))
    {

CAd

 do { System.out.println("Enter Dollars:");
Scanner in = new Scanner(System.in);
String d = in.next();
if ("Q".equalsIgnoreCase(d)) {
    System.out.println("Stop!");
    break;
} else {
try {
        double ds = Double.parseDouble(d);
        one.setDollar(ds);
        System.out.println("Canadian Dollar:");
        System.out.println("$"+one.getCurrencyC());
    } catch (NumberFormatException e) {
        System.out.println("Not double,wrong input");
    }
}
 } while (true);

 }
}
   }
  }

一开始我试着使用while循环，但它不起作用。

Answer 1

现有代码的主要问题是复本在三个不同的地方具有相同的逻辑。相反，您要做的是将所有不同情况下常见的代码分组到方法中，或者以其他方式构造您的逻辑，这样您就不必重复它了。

下面是一种以更易读和更可维护的方式构造代码的方法：

public static void main(String[] args) {

    CurrencyConverter one = new CurrencyConverter();

    do{
        System.out.println("Convert dollar to euro/gbp/cad");

        System.out.println("enter euro/gbp/cad");
        System.out.println("");
        Scanner input = new Scanner(System.in);
        String a = input.next();

        String d = enterDollars();

        if( d == null )
            break;

        try {
            double ds = Double.parseDouble(d);
            one.setDollar(ds);

            if( "euro".equalsIgnoreCase(a) )
                System.out.println("Euro:\n€" + one.getCurrencyE());
            else if( "gbp".equalsIgnoreCase(a) )
                System.out.println("GBP:\n£" + one.getCurrencyG());
            else if( "cad".equalsIgnoreCase(a) )
                System.out.println("Canadian Dollar:\n$" + one.getCurrencyC());
        }
        catch (NumberFormatException e) {
            System.out.println("Not double,wrong input");
        }

    } while (true);

}


private static String enterDollars(){
    System.out.println("Enter Dollars:");
    Scanner in = new Scanner(System.in);
    String d = in.next();

    if ("Q".equalsIgnoreCase(d)) {
        System.out.println("Stop!");
        return null;
    } 

    return d;
}

我已经将用户输入的代码放入了它自己的单独方法中，这使得代码更容易阅读。类似地，您可以进一步将代码划分为更小的方法(如enterCurrency()、presentResult()等)，以提高主方法的可读性。

Answer 2

您正在复制和粘贴类似的逻辑片段。这不是很好的实践，通常意味着您应该开始为类似的行为创建函数。我不知道您在编程中有多深入，所以我将向您展示一种简单的方法，通过使用一个do/while和另一个do同时获取有效的美元金额从用户那里获取输入。

把这个放进你的主

    CurrencyConverter one= new CurrencyConverter();
    Scanner input = new Scanner(System.in);
    System.out.println("Convert dollar to euro/gbp/cad");
    HashSet<String> conversions = new HashSet<>();
    conversions.add("euro"); 
    conversions.add("gdp"); 
    conversions.add("cad");

    System.out.println("");
    String userInput = "";
    do {
        System.out.println("enter euro/gbp/cad");
        userInput = input.nextLine();
        double amount = 0;
        //check to see if we need to get a dollar amount
        if(conversions.contains(userInput))
        {
            do {
                System.out.println("Enter Dollars:");
                String sAmount = input.nextLine();
                amount = Double.MAX_VALUE;
                //check it's a number before parsing
                if(sAmount.matches("\\d+"))
                {
                    amount = Double.parseDouble(sAmount);
                    //then set it for the object once
                    one.setDollar(amount);
                }
                else
                {
                    System.out.println("Error when parsing dollar amount: " + sAmount);
                    System.out.println("Please Try again!");
                }

            } while (amount != Double.MAX_VALUE);
        }
        //check for euro
        if(userInput.equals("euro"))
        {
            System.out.println("Euro: ");
            System.out.println("€"+one.getCurrencyE());
        }
        else if(userInput.equals("gdp"))
        {
            System.out.println("GDP: ");
            System.out.println("£"+one.getCurrencyG());
        }
        else if(userInput.equals("cad"))
        {
            System.out.println("Canadian Dollar: ");
            System.out.println("$"+one.getCurrencyC());
        }
        else if (!userInput.equals("quit"))
        {
            System.out.println("Error with input : " + userInput);
        }
    } while (!userInput.equals("quit"));