Question

我试图编写采用三角形顶点（将是用户输入）的Java代码并输出所述三角形的区域。我得到NaN作为回复。我应该将我的类型改成浮动吗？我是否采取了更长的路线尝试解决这个问题？

使用的公式是距离公式和苍鹭公式。

import java.util.Scanner;

public class TriangleArea {

    public static void main(String[]args){

        Scanner user = new Scanner(System.in);

        System.out.println("To compute the area of a triangle, please input a point in a vertex when prompted");

        System.out.println("Please input X of the first vertex: x ");
        double firstVertexX = user.nextDouble();

        System.out.println("Please input Y of the first vertex: y ");
        double firstVertexY = user.nextDouble();        

        System.out.println("Please input X  of the second vertex: x");
        double secondVertexX = user.nextDouble();

        System.out.println("Please input Y of the second vertex: y ");
        double secondVertexY = user.nextDouble();       

        System.out.println("Please input X of the third vertex: x");
        double thirdVertexX = user.nextDouble();

        System.out.println("Please input Y of the third vertex: y");
        double thirdVertexY = user.nextDouble();        

        double sideOneX = Math.pow(firstVertexX * 1, 2) - Math.pow(secondVertexX * 2, 2);
        double sideOneY = Math.pow(firstVertexY * 1, 2) - Math.pow(secondVertexY * 2, 2);
        double sideOne = Math.pow(sideOneX + sideOneY, .5);

        double sideTwoX = Math.pow(secondVertexX * 1, 2) - Math.pow(thirdVertexX * 2, 2);
        double sideTwoY = Math.pow(secondVertexY * 1, 2) - Math.pow(thirdVertexY * 2, 2);
        double sideTwo = Math.pow(sideTwoX + sideTwoY, .5);

        double sideThreeX = Math.pow(thirdVertexX * 1, 2) - Math.pow(firstVertexX * 2, 2);
        double sideThreeY = Math.pow(thirdVertexY * 1, 2) - Math.pow(firstVertexY * 2, 2);
        double sideThree = Math.pow(sideThreeX + sideThreeY, .5);

        double s = (sideOne + sideTwo + sideThree)/2;

        double areaStepOne = (s - sideOne) * (s - sideTwo) * (s - sideThree);
        double areaStepTwo = s * areaStepOne;
        double area = Math.pow(areaStepTwo, .5);

        System.out.println("The area of the triangle is " + area + ".");

        System.out.println("The area of the triangle is " + area);

    }
}

Answer 1

这个问题是错误的估计。

从（x1，y1）到（x2，y2）的线段长度为sqrt（（x1-x2）^ 2 +（y1-y2）^ 2）。

你要计算的是：sqrt（x1 ^ 2 - （x2 * 2）^ 2 + y1 ^ 2 - （y2 * 2）^ 2）。这可能是消极的，给你NaN。

我将这些行更改为：

double sideOneX = firstVertexX - secondVertexX;
double sideOneY = firstVertexY - secondVertexY;
double sideOne = Math.sqrt(sideOneX * sideOneX + sideOneY * sideOneY);

（您可以使用Math.sqrt(v)代替Math.pow(v, .5)。）

Answer 2

我建议你使用更简单的分析公式

|(X2 - X0) (Y1 - Y0) - (X1 - X0) (Y2 - Y0)| / 2

没有取绝对值，符号会告诉您三角形是顺时针还是逆时针。

从三角形的顶点访问区域

2 个答案: