7、根据要求写代码： (1) 定义接口Shape，包括属性PI和求面积方法getArea() (2) 定义圆类Circle，实现接口Shape，包括属性半径radius，提供带参构造，重写接口的求面积方法，增加求周长的方法getPerimeter (3) 定义圆柱体类Cylinder，继承圆类Circle，增加高度属性height，提供带参构造，重写求面积的方法getArea，增加求体积的方法getVolume (4) 测试类中分别创建圆类和圆柱体类对象，调用各自的方法

(1) 定义接口Shape

public interface Shape {
    double PI = 3.14;
    double getArea();
}

(2) 定义圆类Circle

public class Circle implements Shape {
    private double radius;

    public Circle(double radius) {
        this.radius = radius;
    }

    @Override
    public double getArea() {
        return PI * radius * radius;
    }

    public double getPerimeter() {
        return 2 * PI * radius;
    }
}

(3) 定义圆柱体类Cylinder

public class Cylinder extends Circle {
    private double height;

    public Cylinder(double radius, double height) {
        super(radius);
        this.height = height;
    }

    @Override
    public double getArea() {
        return 2 * super.getArea() + 2 * PI * getRadius() * height;
    }

    public double getVolume() {
        return super.getArea() * height;
    }

    public double getHeight() {
        return height;
    }
}

(4) 测试类

public class Test {
    public static void main(String[] args) {
        Circle circle = new Circle(3);
        System.out.println("圆的面积：" + circle.getArea());
        System.out.println("圆的周长：" + circle.getPerimeter());

        Cylinder cylinder = new Cylinder(3, 5);
        System.out.println("圆柱体的底面积：" + cylinder.getArea());
        System.out.println("圆柱体的体积：" + cylinder.getVolume());
        System.out.println("圆柱体的高度：" + cylinder.getHeight());
    }
}