java - 程序打印使圆柱面积，体积，范围和继承Java保持打印0.0

我尝试了几种不同的方法。要求我使用继承来扩展这些类。每次我运行程序时，它的体积和面积就是0.0。半径显示正确。输出在底部。

public class Base_HW04Q1
{
    public double pi = 3.14, l, radius, height, area, volume;

    public static class RoundShape extends Base_HW04Q1 {
        public RoundShape(double radius) {
            this.radius = radius;
        }
        public double calcArea () {
            area = (radius * radius) * pi;
            return area;
        }
        public String toString() {
            return "A Round Shape of radius: " + radius + ", area " + area + ".";
        }
    }


    public static class Cylinder extends Base_HW04Q1
    {
        public Cylinder(double radius, double height) {
            this.radius = radius;
            this.height = height;
        }
        public double calcArea() {
            l = Math.sqrt((radius * radius) + (height * height));
            area = 2 * pi * radius * height + 2 * pi * l;
            return area;
        }
        public double calcVolume() {
            volume = pi * (radius * radius) * height;
            return volume;
        }
        public String toString() {
            return "A Cylinder of radius: " + radius + ", area " + area + " and a volume of " + volume;
        }
    }


    public static class Cone extends Base_HW04Q1 //TODO: This line is almost, but not quite, complete.
    {
        public Cone(double radius, double height) {
            this.radius = radius;
            this.height = height;
        }
        public double calcArea() {
            l = Math.sqrt((radius * radius) + (height * height));
            area = (pi * radius * l) + (pi * radius * radius);
            return area;
        }
        public double calcVolume() {
            volume = 0.333 * pi * radius * radius * height;
            return volume;
        }
        public String toString() {
            return "A Cone of radius: " + radius + ", area " + area + " and a volume of " + volume;
        }
    }

    public static void main(String[] args)
    {
        //object creation
        Cylinder Cylinder1 = new Cylinder(30, 10);
        Cone Cone1 = new Cone(10, 20);
        RoundShape RoundShape1 = new RoundShape(50);

        //print for objects
        System.out.println(Cylinder1);
        System.out.println(RoundShape1);
        System.out.println(Cone1);
    }
}

输出：


  半径为30.0，面积为0.0，体积为0.0的圆柱体圆形
  半径：50.0，面积0.0。半径为10.0，面积为0.0和
  数量0.0

最佳答案

您的toString()永远不会调用进行计算的方法，而是打印默认的0.0字段值。如果在调用toString()方法之前（即在为计算字段指定适当值之前）调用过calcXxxx()，您将冒此风险。最好的解决方案是，首先完全消除计算值的字段（例如面积和体积），以防止发生此问题。而是在toString（）中，调用方法以获取这些值。

例如。，

public double pi = 3.14, l, radius, height; // , area, volume;

public static class RoundShape extends Base_HW04Q1 {
    public RoundShape(double radius) {
        this.radius = radius;
    }
    public double calcArea () {
        return (radius * radius) * pi;
        // return area;
    }
    public String toString() {
        return "A Round Shape of radius: " + radius + ", area " + calcArea() + ".";
    }
}

关于java - 程序打印使圆柱面积，体积，范围和继承Java保持打印0.0，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/40230438/