class Polygon (slide 2 of 3)

public double area() {

if (vertices.size() < 3) return 0.0;

Enumeration enum = vertices.elements();

Point firstVertex = (Point) enum.nextElement();

Point lastVertex = firstVertex;

double total = 0.0;

while(enum.hasMoreElements()) {

Point thisVertex = (Point) enum.nextElement();

total += areaUnderSegment(lastVertex, thisVertex);

lastVertex = thisVertex;

}

total += areaUnderSegment(lastVertex, firstVertex);

return total;

}

private double areaUnderSegment(Point p1, Point p2) {

return (p1.x - p2.x) * (p1.y + p2.y) / 2;

}