java - 为什么我的构造函数参数没有传递？

Question

这是我的类(class)。在底部的 main 方法中，我在构造函数中传递两个参数(int numTriangles，双半径)作为 (8,1)。在顶部 radius 和 numTriangles 声明的变量应采用这些值，因为我的构造函数分配它们然后运行计算。然而，当计算twoTheta时，我会得到除以零的错误，因为此时numTriangles为零。这是为什么？我该如何解决它？谢谢。

package Triangles;

public class Triangles {

    double radius;
    int numTriangles;
    double twoTheta = 360/numTriangles;
    double theta = twoTheta / 2;
    double base;
    double height;
    double result;
    double halfTriangleArea;
    double triangleArea;
    double area;

    public Triangles(int numTriangles, double radius) {
        this.numTriangles = numTriangles;
        this.radius = radius;
        runCalculation();
    }

    // My methods

    public double calculateBase() { // SOH
        double thetaToRadians = Math.toRadians(theta);
        double base = Math.sin(thetaToRadians) / radius;
        return base;
    }

    public double calculateHeight() { // CAH
        double thetaToRadians = Math.toRadians(theta);
        double height = Math.cos(thetaToRadians) / radius;
        return height;
    }

    public double checkPythag(double base, double height) {
        double a = base;
        double b = height;
        double result = Math.sqrt(a*a + b*b);
        return result;
    }

    public double calculateArea(double base, double height) {
        double halfTriangleArea = (0.5) * base * height;
        return halfTriangleArea;
    }

    public double runCalculation() {
        base = calculateBase();
        height = calculateHeight();
        result = checkPythag(base, height);
        halfTriangleArea = calculateArea(base, height); 
        triangleArea = 2 * halfTriangleArea;
        // C = Pi * D = Pi * 2 * r
        // A = Pi * r.^2
        area = numTriangles * triangleArea;
        // Substitute Pi for X
        // area = X * r.^2
        // if r is 1
        // area = X
        return area;
    }

    // Runnable

    public static void main(String[] args) { // create an instance of class to run in main
        Triangles triangles = new Triangles(8, 1);
        System.out.println("radius: " + triangles.radius);
        System.out.println("numTriangles: " + triangles.numTriangles);
        System.out.println("twoTheta " + triangles.twoTheta);
        System.out.println("theta " + triangles.theta);
        System.out.println("base: " + triangles.base);
        System.out.println("height: " + triangles.height);
        System.out.println("checkPythag " + triangles.result + " | " + triangles.radius);
        System.out.println("halfTriangleArea: " + triangles.halfTriangleArea);
        System.out.println("triangleArea: " + triangles.triangleArea);
        System.out.println("Approximation of Pi by triangles: " + triangles.area);
    }   
}

Answer 1

正如多个答案所指出的，twoTheta(以及 theta)是在调用构造函数之前初始化的，因此会出现错误。

我建议您在构造函数内部初始化twoTheta和theta。

 public Triangles(int numTriangles, double radius) {
    this.numTriangles = numTriangles;
    this.radius = radius;
    //Initialize twoTheta
    this.twoTheta = 360/this.numTriangles;
    this.theta = this.twoTheta/2;
    runCalculation();
}