Question

作为初学者，我无法真正理解此代码中的问题：

package Currency;

import java.util.Scanner;

public class Currency {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double value1 = 0.00, value2 = 0.00;
        String currency;

        System.out.print("Enter a value: ");
        value1 = input.nextDouble();
        System.out.print("USD or EUR: ");
        currency = input.nextLine();


        if(currency.equals("USD")){
            value2 = value1 * 0.734878047;
            System.out.println(value1 + "USD = " + value2 + " EUR. (Conversion rate: 1 USD = 0.734878047 EUR)");
        } else if (currency.equals("EUR")) {
            value2 = value1 * 1.36077;
            System.out.println(value1 + "EUR = " + value2 + " USD. (Conversion rate: 1 EUR = 1.36077 USD)");
        } else {
            System.out.println("Conversion rate: 1 USD = 0.734878047 EUR"
            + "\nConversion rate: 1 EUR = 1.36077 USD");
        }

        input.close();

    }

}

不知何故，它甚至没有读取第二个输入，但只是打印最后一个。任何人都可以帮助我做到这一点吗？：）

提前谢谢。

Answer 1

似乎input.nextLine();正在用户在第一次提示后点击输入时在换行符中读取。

快速修复可能会在您提示input.nextLine()或USD之前添加另一个EUR“虚拟”来电：

package Currency;

import java.util.Scanner;

public class Currency {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double value1 = 0.00, value2 = 0.00;
        String currency;

        System.out.print("Enter a value: ");
        value1 = input.nextDouble();
        input.nextLine();
        System.out.print("USD or EUR: ");
        currency = input.nextLine();

        if(currency.equals("USD")){
            value2 = value1 * 0.734878047;
            System.out.println(value1 + "USD = " + value2 + " EUR. (Conversion rate: 1 USD = 0.734878047 EUR)");
        } else if (currency.equals("EUR")) {
            value2 = value1 * 1.36077;
            System.out.println(value1 + "EUR = " + value2 + " USD. (Conversion rate: 1 EUR = 1.36077 USD)");
        } else {
            System.out.println("Conversion rate: 1 USD = 0.734878047 EUR"
                    + "\nConversion rate: 1 EUR = 1.36077 USD");
        }

        input.close();
    }
}

Answer 2

我认为点击返回键会对下一个读取线产生影响。如下所示做一个小改动似乎解决了这个问题：

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    double value1 = 0.00, value2 = 0.00;
    String currency;

    System.out.print("Enter a value: ");
    String str = input.nextLine();
    value1 = Double.parseDouble(str);
    System.out.print("USD or EUR: ");
    currency = input.nextLine();


    if(currency.equals("USD")){
        value2 = value1 * 0.734878047;
        System.out.println(value1 + "USD = " + value2 + " EUR. (Conversion rate: 1 USD = 0.734878047 EUR)");
    } else if (currency.equals("EUR")) {
        value2 = value1 * 1.36077;
        System.out.println(value1 + "EUR = " + value2 + " USD. (Conversion rate: 1 EUR = 1.36077 USD)");
    } else {
        System.out.println("Conversion rate: 1 USD = 0.734878047 EUR"
        + "\nConversion rate: 1 EUR = 1.36077 USD");
    }

    input.close();
}

示例：

Enter a value: 25
USD or EUR: USD
25.0USD = 18.371951175 EUR. (Conversion rate: 1 USD = 0.734878047 EUR)

或者，因为在您的情况下，您期望一个没有任何空格的字符串，您可以使用.next()属性，并保留您的代码：

   public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    double value1 = 0.00, value2 = 0.00;
    String currency;

    System.out.print("Enter a value: ");
    value1 = input.nextDouble();
    System.out.print("USD or EUR: ");
    currency = input.next();


    if(currency.equals("USD")){
        value2 = value1 * 0.734878047;
        System.out.println(value1 + "USD = " + value2 + " EUR. (Conversion rate: 1 USD = 0.734878047 EUR)");
    } else if (currency.equals("EUR")) {
        value2 = value1 * 1.36077;
        System.out.println(value1 + "EUR = " + value2 + " USD. (Conversion rate: 1 EUR = 1.36077 USD)");
    } else {
        System.out.println("Conversion rate: 1 USD = 0.734878047 EUR"
        + "\nConversion rate: 1 EUR = 1.36077 USD");
    }

    input.close();

}

Answer 3

在两种情况下if子句中的

都使用currency.trim().equals(...删除字符串开头或结尾的任何空格。

Java编程，货币计算器

3 个答案: