当我用逗号或小数点分隔小数时，扫描会翻倍

我是Java的新手，当时我在做一个简单的计算器。问题是，当我输入的数字是 3.1时，它会给出异常错误，但是在写 3,1时，它就可以了。

I'm rather new to Java and I was making a simple calculator. Problem is when I my input number is for example "3.1" it gives an exception error, but when writing "3,1" it works just fine.

我的朋友，但是，它有一个更高级的计算器（带有字符串解析），当我运行他的代码时，情况恰恰相反：3,1给出了异常错误，3.1可以正常工作。

My friend, however, has a slightly more advanced calculator (with string parsing) and when I run his code the opposite happens: 3,1 gives exception error, 3.1 works perfectly.

I我很想知道是什么原因导致了这些不同的行为。

I was looking forward to know what causes these different behaviors.

我刚才做了一个简单的总结，同样的事情发生了，我将编辑他的计算器代码，分钟

I made this simple sum just now and the same happens, I'll edit and put his calculator code in a few minutes

import java.util.Scanner;

public class Tutorial_7 {
    public static void main(String args[]){
        Scanner scan = new Scanner(System.in);
        double num1, num2;

        System.out.println("Introduza os dois números");

        System.out.println("1º: ");
        num1 = scan.nextDouble();
        System.out.println("2º: ");
        num2 = scan.nextDouble();

        System.out.println((num1 + num2));
        scan.close();
    }

}

最终编辑：他确实使用 Double.parseDouble（）。知道了，区别确实在于它的本地化。本来应该寻找它，但之前从未听说过这个概念。

Final edit: He does use Double.parseDouble(). Got it, the difference is indeed in where it is localized. Should have looked for it but never heard of this concept before.

谢谢