java - 当输入不是 "q"并且不使用扫描仪加倍时如何输出错误

Question

public class CurrencyConverter
{
double dollar;
double rate; //constructors
double euro;

//构造函数

public CurrencyConverter()
{
    dollar=0;
    rate=0.95;
}

//对象

public void setDollar(double d)
{
     dollar= d;
}
public double getCurrency()
{
 euro= rate*dollar;
 return euro;

当输入不是“q”并且代码中不是 double 时如何输出错误我尝试使用 if 方法，但它不起作用

import java.util.Scanner;

public class CurrencyTester {

    private static Scanner in;

    public static void main(String[] args) {

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

        do {
            System.out.println("Enter Dollars:");
            in = new Scanner(System.in);
            String d = in.next();
            if ("Q".equalsIgnoreCase(d)) {
                System.out.println("Stop!");
                break;
            } else {
                double ds = Double.parseDouble(d);
                one.setDollar(ds);
                System.out.println("Euro:");
                System.out.println(one.getCurrency());
            }
        } while (true);

    }
}

Answer 1

当您检查输入是否为 q 时，第一部分是正确的，您需要检查输入是否为 double，因此您可以使用 try{}catch(){}像这样:

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 {
        //check if your input is valid double or not, if not show an error message
        try {
            double ds = Double.parseDouble(d);
            one.setDollar(ds);
            System.out.println("Euro:");
            System.out.println(one.getCurrency());
        } catch (NumberFormatException e) {
            System.out.println("*********Not double*********");
        }
    }
} while (true);