APCS_CH8_Polygon.java

//Polygon.java      MrG     2013.0208
import java.util.ArrayList;
public class Polygon
{
    private ArrayList<Point> vertices;

    public Polygon()
    {
        vertices = new ArrayList<Point>();
    }

    public void add(Point p)
    {
        vertices.add(p);
    }

    public String toString()
    {
        return "" + vertices;
    }

    public double getArea()
    {
        int stop=vertices.size();
        double sum=0;
        for(int i=0; i<stop;i++)
        {
            sum+=vertices.get(i).getX()*vertices.get((i+1)%stop).getY();
            sum-=vertices.get((i+1)%stop).getX()*vertices.get(i).getY();
        }
        return sum/2;
    }
}