计算多边形面积（JAVA）

import java.util.*;class point{public int x;public int y;point(){this.x=0;this.y=0;}}public class caculateArea {    public static float caculate(point vertex[],int pointNum)    {    int i=0;    float temp=0;    for(;i<pointNum-1;i++)    {    temp+=(vertex[i].x-vertex[i+1].x)*(vertex[i].y+vertex[i+1].y);    }    temp+=(vertex[i].x-vertex[0].x)*(vertex[i].y+vertex[0].y);    return temp/2;    }        public static void main(String args[])         {        point[] vertex=new point[100];        int pointNum=0;        Scanner in = new Scanner(System.in);        for(int i=0;i<100;i++)        {        vertex[i]= new point();        }        System.out.println("请输入多边形顶点数,个数不能超过100个(逆时针）：");        pointNum=in.nextInt();        for(int i=0;i<pointNum;i++)        {        System.out.println("第"+i+"个顶点的横坐标:");        vertex[i].x = in.nextInt();        System.out.println("第"+i+"个顶点的纵坐标:");        vertex[i].y = in.nextInt();        }        System.out.println("多边形面积是："+caculate(vertex,pointNum));        }}