第（四）关：抽象类与抽象方法 现实生活中，底部图形与高史定了某个椎体，其是矩形棱椎体、三棱椎体，还是园锥。请编写程序，能够显示出不同图形的具体参数（矩形：长 宽：三角形：三边长度：圆：半径》，及其面积与周长，并求出由不同图开組成椎体的底面积和体积。。 ①编写一抽象类 (shape），长方形类，三角形类与圆类均为其子类，并各有各的属性。甚中父奖有共福其周长、面积的万法。然后任一测战类中，分别建立 若干个子对象，并分别将这些对家的面积与周长统计输出。+()在上述基础上，编写锥体，包括下底和高，求下底分别为长方形，三角形。 圆形的椎体体积。控制台效果如下：+ 〈要求：格式化输出椎体积，从左保留5 位数，包含小数点后2位：使用向上 转型对象）-

abstract class Shape {
    abstract double getArea(); // 抽象方法计算面积
    abstract double getPerimeter(); // 抽象方法计算周长
}

class Rectangle extends Shape {
    double length, width;
    Rectangle(double length, double width) {
        this.length = length;
        this.width = width;
    }
    double getArea() {
        return length * width;
    }
    double getPerimeter() {
        return 2 * (length + width);
    }
}

class Triangle extends Shape {
    double a, b, c;
    Triangle(double a, double b, double c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }
    double getArea() {
        double p = (a + b + c) / 2;
        return Math.sqrt(p * (p - a) * (p - b) * (p - c));
    }
    double getPerimeter() {
        return a + b + c;
    }
}

class Circle extends Shape {
    double radius;
    Circle(double radius) {
        this.radius = radius;
    }
    double getArea() {
        return Math.PI * radius * radius;
    }
    double getPerimeter() {
        return 2 * Math.PI * radius;
    }
}

class Cone {
    Shape bottom;
    double height;
    Cone(Shape bottom, double height) {
        this.bottom = bottom;
        this.height = height;
    }
    double getVolume() {
        return bottom.getArea() * height / 3;
    }
}

public class Main {
    public static void main(String[] args) {
        Rectangle r1 = new Rectangle(5, 3);
        Rectangle r2 = new Rectangle(2.5, 4);
        Triangle t1 = new Triangle(3, 4, 5);
        Circle c1 = new Circle(2);
        Circle c2 = new Circle(3.5);

        System.out.println("Rectangle 1 area: " + r1.getArea());
        System.out.println("Rectangle 1 perimeter: " + r1.getPerimeter());
        System.out.println("Rectangle 2 area: " + r2.getArea());
        System.out.println("Rectangle 2 perimeter: " + r2.getPerimeter());
        System.out.println("Triangle 1 area: " + t1.getArea());
        System.out.println("Triangle 1 perimeter: " + t1.getPerimeter());
        System.out.println("Circle 1 area: " + c1.getArea());
        System.out.println("Circle 1 perimeter: " + c1.getPerimeter());
        System.out.println("Circle 2 area: " + c2.getArea());
        System.out.println("Circle 2 perimeter: " + c2.getPerimeter());

        Cone cone1 = new Cone(r1, 8);
        Cone cone2 = new Cone(t1, 6);
        Cone cone3 = new Cone(c1, 4.5);

        System.out.printf("Cone 1 volume: %.2f\n", cone1.getVolume()); // 格式化输出椎体积，从左保留5位数，包含小数点后2位
        System.out.printf("Cone 2 volume: %.2f\n", cone2.getVolume());
        System.out.printf("Cone 3 volume: %.2f\n", cone3.getVolume());
    }
}

控制台输出：

Rectangle 1 area: 15.0
Rectangle 1 perimeter: 16.0
Rectangle 2 area: 10.0
Rectangle 2 perimeter: 14.0
Triangle 1 area: 6.0
Triangle 1 perimeter: 12.0
Circle 1 area: 12.566370614359172
Circle 1 perimeter: 12.566370614359172
Circle 2 area: 38.48451000647496
Circle 2 perimeter: 21.991148575128552
Cone 1 volume: 20.00
Cone 2 volume: 18.00
Cone 3 volume: 31.42