public class Circle { protected double radius; public Circle(double radius) { this.radius = radius; } public double area() { return 3.14 * radius * radius; }}public class Cylinder extends Circle { private double height; public Cylinder(double radius, double height) { super(radius); this.height = height; } public double volume() { return area() * height; }}无法输出结果

这个代码只是定义了两个类，没有进行任何的输出操作，因此不会有任何结果输出。如果你想要测试一下 `Cylinder` 类的功能，可以在代码中添加一些输出语句，例如：

public static void main(String[] args) {
    Cylinder cylinder = new Cylinder(2.0, 5.0);
    System.out.println("底面圆的面积为：" + cylinder.area());
    System.out.println("圆柱的体积为：" + cylinder.volume());
}

在这个示例中，我们新建了一个 `Cylinder` 对象，并使用该对象的 `area` 和 `volume` 方法来计算底面圆的面积和圆柱的体积，并通过 `System.out.println` 方法将结果输出到控制台。

希望这可以帮助到你！

相关问题

已知Point(点)类，点类的公有派生类Circle(圆)类，圆类的公有派生Cylinder(圆柱体)类如下： class Point { public: virtual double area() { return 0; } }; class Circle:public Point { protected: double m_radius; public: Circle(double r); virtual double area(); }; class Cylinder:public Circle { private: double m_high; public: Cylinder(double r, double h); virtual double area(); }; 试完成成员函数的定义，在主函数中输入圆的半径和圆柱的高，利用指向基类的指针，分别输出圆的面积和圆柱体的表面积。 Input 2个数，分别代表圆的半径和圆柱的高。 Output 圆的面积和圆柱体的表面积(取2位小数)。 Sample Input 1 1.5 2 Sample Output 1 7.06 32.97用c++写出此代码

#include <iostream>
#include <iomanip>
using namespace std;

class Point {
public:
    virtual double area() { return 0; }
};

class Circle : public Point {
protected:
    double m_radius;
public:
    Circle(double r) : m_radius(r) {}
    virtual double area() { return 3.14 * m_radius * m_radius; }
};

class Cylinder : public Circle {
private:
    double m_high;
public:
    Cylinder(double r, double h) : Circle(r), m_high(h) {}
    virtual double area() { return 2 * Circle::area() + 2 * 3.14 * m_radius * m_high; }
};

int main() {
    double r, h;
    cin >> r >> h;
    Point* p1 = new Circle(r);
    Point* p2 = new Cylinder(r, h);
    cout << fixed << setprecision(2) << p1->area() << " " << p2->area() << endl;
    delete p1;
    delete p2;
    return 0;
}

用C++编写一个程序满足已知抽象类Shape及Shape类的3个公有派生类圆类Circle、矩形类Rectangle、三角形类Triangle声明如下： class Shape { public: virtual double area() const = 0; }; class Circle:public Shape { public: Circle(double r); virtual double area() const; protected: double m_radius; }; class Rectangle:public Shape { public: Rectangle(double w, double h); virtual double area() const; protected: double m_width, m_height; }; class Triangle:public Shape { public: Triangle(double a, double b, double c); virtual double area() const; protected: double m_a, m_b, m_c; }; 试完成成员函数的定义，在主函数中输入圆的半径、矩形的宽和高、三角形的三条边，定义对象，利用函数void printArea(const Shape &s)输出圆、矩形及三角形的面积。 输入 三行，第1行圆的半径，第2行矩形的宽和高，第3行三角形的三条边。 输出 圆、矩形及三角形的面积(取2位小数)。

以下是代码实现：

#include <iostream>
#include <iomanip>
#include <cmath>

using namespace std;

class Shape {
public:
    virtual double area() const = 0;
};

class Circle:public Shape {
public:
    Circle(double r) {
        m_radius = r;
    }
    virtual double area() const {
        return 3.14 * m_radius * m_radius;
    }
protected:
    double m_radius;
};

class Rectangle:public Shape {
public:
    Rectangle(double w, double h) {
        m_width = w;
        m_height = h;
    }
    virtual double area() const {
        return m_width * m_height;
    }
protected:
    double m_width, m_height;
};

class Triangle:public Shape {
public:
    Triangle(double a, double b, double c) {
        m_a = a;
        m_b = b;
        m_c = c;
    }
    virtual double area() const {
        double p = (m_a + m_b + m_c) / 2.0;
        return sqrt(p * (p - m_a) * (p - m_b) * (p - m_c));
    }
protected:
    double m_a, m_b, m_c;
};

void printArea(const Shape &s) {
    cout << fixed << setprecision(2) << "面积为：" << s.area() << endl;
}

int main() {
    double r, w, h, a, b, c;
    cin >> r >> w >> h >> a >> b >> c;

    Circle circle(r);
    Rectangle rectangle(w, h);
    Triangle triangle(a, b, c);

    cout << "圆的";
    printArea(circle);

    cout << "矩形的";
    printArea(rectangle);

    cout << "三角形的";
    printArea(triangle);

    return 0;
}

输入示例：

2
3 4
3 4 5

输出示例：

圆的面积为：12.56
矩形的面积为：12.00
三角形的面积为：6.00