当我输入整数，如5，7，14等，一切正常。但是当我输入例如7.5时，我得到一个错误。错误在哪里？

Exception in thread "main" java.util.InputMismatchException
    at java.base/java.util.Scanner.throwFor(Scanner.java:939) 
    at java.base/java.util.Scanner.next(Scanner.java:1594) 
    at java.base/java.util.Scanner.nextDouble(Scanner.java:2564) 
    at Exercise_11.main(Exercise_11.java:8)

下面是代码：

import java.util.Scanner;
    public class Exercise_11 {
    public static void main(String[] args) {
    Scanner radius = new Scanner(System.in);
    System.out.print("Please input the radius of circle: ");
    double r= radius.nextDouble();
    double l= 2*Math.PI*r;
    double s= Math.PI*r*r;
    System.out.println("Length = " + l);
    System.out.println("Area = " + s);
    }
    }