計算一個n角度的角度（加上比較）

Question

我想要計算n角形狀的點之間的角度。有2個數組可以保存x和y座標。我不斷收到P13的錯誤，我無法弄清楚原因。有誰知道一個原因？

public class Ugao { 

    public static int nizovi(double[]a , double[]b , double alfa) { 
     int BrStr = 0; 
     for (int i = 0; i < b.length; i++) { 
      double P12,P13, P23; 
      P12 = duzina(a[i+1], b[i+1], a[i], b[i]); 
      P13 = duzina(a[i+1], b[i+1], a[i+2], b[i+2]); // pisemo prvo i+1 jer je to vertex tacka, ona koja je u centru ugla, zato nije od i 
      P23 = duzina(a[i], b[i], a[i+2], b[i+2]); 

      double x = ugao(P12, P13, P23); 
      if(x > alfa) { 
       System.out.print("Stranica : " + "(" + a[i] + "," + b[i] + ")" + "(" + a[i+1] + "," + b[i+1] + ")" + " & "); 
       System.out.println("(" + a[i+1] + "," + b[i+1] + ")" + "(" + a[i+2] + "," + b[i+2] + ")"); 
       System.out.println(); 
       BrStr++; 
      } 
     } 
     return BrStr; 
    } 


    public static double ugao (double P12, double P13, double P23) { 
     return Math.acos((Math.pow(P12, 2) + Math.pow(P13, 2) - Math.pow(P23, 2))/(2 * P12 * P13)); 
    } 

    public static double duzina (double vertexX1, double vertexY1, double x2, double y2) { 
     return Math.sqrt(Math.pow((vertexX1-x2),2)+ Math.pow((vertexY1-y2), 2)); 
    } 

    public static void main(String[] args) { 
     // TODO Auto-generated method stub 

     double a[] = {12,25,3}; 
     double b[] = {11,20,5}; 

     nizovi(a, b, 45); 

    } 

} 

Answer 1

您正在用完數組範圍。

例如，如果length = 4數組包含索引0..3，但在與i=3表達運行的最後一個週期a[i+2]想元素a[5]

可以使用模運算來獲得下一個頂點指數

current: i 
next: (i+1)%length 
nextnext: (i+2)%length