英文:
How to store a value in variable as a double from user input?
问题
我刚开始学习Java编程，但是我无法弄清楚如何将用户输入的值存储为double类型。
以下是我的代码：
package FirstProject;
import java.util.Scanner;
public class TripPlanner {
public static void main() {
Scanner console = new Scanner(System.in);
System.out.print("在1美元中有多少" + currencySymbol + "？ ");
double conversion = console.nextDouble();
}
}
我不明白为什么当我输入例如19.5时，它会给我一个异常错误。我理解我将conversion变量定义为double类型（double conversion），并且我期望用户输入一个double类型（console.nextDouble();）。这是很基础的问题，但是作为从Python转过来的，我无法理解我做错了什么。
英文:
I've only just started learning programming in Java and I cannot figure out how to store a value from user input as a double.
Here's my code:
package FirstProject;
import java.util.Scanner;
public class TripPlanner {
public static void main () {
Scanner console = new Scanner(System.in);
System.out.print("How many " + currencySymbol + " are there in 1 USD? ");
double conversion = console.nextDouble();
}
}
I don't understand why when I enter, for example 19.5, it gives me exception error. My understanding is that I defined the conversion variable as double (double conversion) and I expect the user to enter a double (console.nextDouble();). It's fundamental but coming from Python I can't understand what I'm doing wrong.
答案1
得分: 2
使用像您所做的这样的扫描器有点不受控制。例如，扫描器期望的格式是与区域设置相关的。如果您的系统设置为德语，那么您需要输入3,7来表示3.7的双精度值。
如果输入的字符串格式无效，那么可能会引发异常，通常是java.util.InputMismatchException。您应该捕获异常并以适合您的用例的方式做出反应。
为了更好地控制所使用的区域设置，您应该从控制台中读取一个字符串，然后例如使用java.text.NumberFormat。请参考此问题。
英文:
Using the Scanner like you did is somewhat uncontrolled. For example, the format the scanner expects is locale-dependent. If your system settings are German, for example, then you need to enter 3,7 for a double value of 3.7.
If the format of the entered string is invalid, then an exception will be thrown, probably java.util.InputMismatchException. You should catch the exception and react in a way that's fit to you use case.
To get better control over the locale used, you should instead read a string from the console and then for example use a java.text.NumberFormat.
See this question.
答案2
得分: 1
@Leisetreter指导我朝着正确的方向。问题出在键盘设置上。我居住在英国，习惯使用点号来表示十进制数。然而，我的键盘设置为波兰程序员模式。在波兰，十进制数使用逗号","来表示。一旦我更改了键盘设置，这个问题就不再存在。我自己可能永远想不到这一点。感谢@Leisetreter。
英文:
@Leisetreter pointed me in the right direction. It was the keyboard settings. I live in the UK and use the conventions of writing a decimal number with a dot. However, my keyboard was set to Polish programmer's. In Poland decimal numbers are written with a ",". Once I changed the settings I did not have that problem anymore. It would have never occurred to me. Thanks @Leisetreter.
答案3
得分: 0
我在你的代码中没有看到任何错误。除了 main 方法。
你应该这样调用她：public static void main (String args[])。
英文:
I don't see any mistake in your code. Except from main.
The proper way you should call her is public static void main (String args[])
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