Java，对货币计算器进行编程，首先停在 JOptionPane 并保持运行

Question

我是一名正在尝试学习 Java 编程的新生。本周我们有一项作业是使用两个类编写一个货币计算器。我在运行程序时遇到了一些问题，即让它继续运行。我们必须使用 JOptionPane 来请求输入和显示输出，我不完全确定我应该如何保留它们 "popping up"。我希望我能得到一些关于我应该如何保留程序的指示运行。

import javax.swing.*;
import java.util.Scanner;

public class runner {
public static void main(String[] args) {

    Scanner input = new Scanner(System.in);

        do
            {
                JOptionPane.showInputDialog(null, "Type in the number of kroner you want to check: ");
                double kroner = input.nextInt();
                Object[] options = {"Euro", "Yen"};
                int choice = JOptionPane.showOptionDialog(null, "you wrote: " + kroner + "do you want to convert this to euro or yen?", "Choose an alternative", JOptionPane.YES_NO_OPTION, JOptionPane.INFORMATION_MESSAGE, null, options, options[0]);

            Functions operationObject = new Functions();

            if (choice == 0)
            {
                operationObject.kronerTilEuro(kroner);
            }
            else if (choice == 1)
            {
                operationObject.kronerTilYen(kroner);
            }
            else
            {
                JOptionPane.showMessageDialog(null, "You need to pick one of the alternatives!");
            }
        }
        while (!input.hasNextInt());
        {
            JOptionPane.showMessageDialog(null, "I am not happy");
            input.next();
        }
    }
}

我曾尝试创建一个循环，以便在用户输入的不是整数但运气不佳时再次显示第一个面板。如果我遗漏了什么，请告诉我。

Answer 1

问题出在这里，您正在使用 showInputDialog 从用户那里读取某物，之后您的程序中有一个 input.nextInt() 而没有任何警告，它一直在等待您输入数字:

JOptionPane.showInputDialog(null, "Type in the number of kroner you want to check: ");
double kroner = input.nextInt();

首先将 input.nextInt() 替换为 input.nextDouble()，您正在阅读 double 而不是 int

我会告诉你两种方法:

1 - 将 showInputDialog 替换为 showMessageDialog :

JOptionPane.showMessageDialog(null, "Type in the number of kroner you want to check: ");
double kroner = in.nextDouble();

2 - 尝试用 showInputDialog 读取并将它的 String 解析为 Double

double kroner = Double.parseDouble(JOptionPane.showInputDialog(null, "Type in the number of kroner you want to check: "));

Answer 2

我想这就是你想要的

public class Runner {

    public static void main(String[] args) {
        // amount
        Double amount = null;
        while (amount == null) {
            String amountStr = JOptionPane.showInputDialog(null, "Type in the numeric amount kroner oyu want to check");
            if(amountStr==null)
                JOptionPane.showMessageDialog(null, "Pleae enter a numeric amount", "Error", JOptionPane.ERROR_MESSAGE);
            else
                try {
                    amount = Double.valueOf(amountStr);
                } catch (NumberFormatException e) {
                    JOptionPane.showMessageDialog(null, "only 0-9 and . are allowed", "Error", JOptionPane.ERROR_MESSAGE);
                }
        }
        // option
        String[] options = new String[] { "-> EUR", "-> YEN" };
        int selection = JOptionPane.showOptionDialog(null, "Please select the target currency", "Title",
                JOptionPane.OK_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, options, null);
        String option = options[selection];
        // result
        JOptionPane.showMessageDialog(null, doSomethingFancy(amount, option), "Result",
                JOptionPane.INFORMATION_MESSAGE);

    }

    private static String doSomethingFancy(Double amount, String option) {
        // here you want to do the calculations
        return amount + " kroener " + option;
    }

}

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