java内部类的定义与使用

class Cube {
    private double height;

    Cube() {}

    Cube(double height) {
        this.height = height;
    }

    public double volume(double area) {
        return area * height;
    }

    public class Rectangle {
        private double width;
        private double length;

        Rectangle(double width, double length) {
            this.width = width;
            this.length = length;
        }

        public double area() {
            return length * width;
        }
    }
}

public class Test {
    public static void main(String[] args) {
        Cube.Rectangle S = new Cube().new Rectangle(10.0, 10.0);
        double s = S.area();
        Cube V = new Cube(20.0);
        double v= V.volume(s);
        System.out.println("立方体的体积 = " + v);
    }
}