java - 简单的Java困惑

Question

我正在学习 Java 计算类(class)，我对导致错误的原因感到困惑。我试图研究它，但我似乎很难搜索这种错误。

ERROR: source_file.java:12: error: cannot find symbol
double r = scan.nextDouble; ^
symbol: variable nextDouble
location: variable scan of type Scanner

代码:

 import java.io.*;
 import static java.lang.System.*;
 import java.util.Scanner;

 class Rextester{


  public static void main (String str[]) throws IOException {

     Scanner scan = new Scanner(System.in);
     System.out.println("Radius:");
     double r = scan.nextDouble;
     double circumference = (2 * 3.14 * r);
     double area = (r * r * 3.14);
     System.out.println("Circumference: " + circumference );
     System.out.println("Area :" + area );

    }

}

Answer 1

方法需要括号

double r = scan.nextDouble();
                          ^