Java无法取消引用double该怎么解决

Java无法取消引用double该怎么解决，求解答！求！在求解答！

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area = Math.Pi * r * r;
r.getArea()肯定也是错的啊，r是double类型，不是Circle类对象啊

double r = in.nextDouble();
Circle circle = new Circle(r);
System.out.printf("圆的面积:%.2f\n",circle.getArea());