Question

我尝试了几种不同的方法。我需要使用继承来扩展这些类。每次我运行程序时，它只会输出0.0的体积和面积。半径显示正确。输出在底部。

get '/player/:playerId' => 'players#show'
get '/player/:playerId/edit' => 'players#edit'

输出：

圆柱半径：30.0，面积0.0，体积为0.0圆形半径：50.0，面积0.0。半径锥：10.0，面积0.0和a 体积为0.0

Answer 1

您的toString()从不调用执行计算的方法，而是打印默认的0.0字段值。如果在调用toString()方法之前调用calcXxxx()，即在计算字段被赋予适当值之前，则会冒这种风险。最好的解决方案是首先通过完全去除计算值的字段（例如面积和体积）来防止此问题发生。而是在toString（）中，调用方法来获取这些值。

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() + ".";
    }
}

Answer 2

这是因为你只是实例化对象并输入到构造函数而不是其他方法。

    Cylinder Cylinder1 = new Cylinder(30, 10);
    Cone Cone1 = new Cone(10, 20);
    RoundShape RoundShape1 = new RoundShape(50);

没有人打电话给这些方法

    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;
    }

和其他方法。如果您想通过以下方法计算，请从构造函数或main中调用它们：

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);

    double roundArea = RoundShape1.calcArea();//then use this
    string roundMessage = RoundShape1.toString();//and this whatever you want.

    //do it in others too

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

对于Cylinder区域，音量，范围+继承java，程序打印保持打印0.0

2 个答案: