# Find area of a polygon

The following java method calculates the sum of a polygon given a list of the points in either clockwise or counter clockwise order:

```private double calculateArea(List<Point> orderedPoints) {
//multiply each x coordinate by the following y
int positiveDiagonalSum = 0;
for (int i = 0; i<orderedPoints.size(); i++){
if (i == orderedPoints.size() - 1){
positiveDiagonalSum += orderedPoints.get(i).x * orderedPoints.get(0).y;
} else {
positiveDiagonalSum += orderedPoints.get(i).x * orderedPoints.get(i+1).y;
}
}

//multiply each y coordinate by the following x
int negativeDiaglonalSum = 0;
for (int i = 0; i<orderedPoints.size(); i++){
if (i == orderedPoints.size() - 1){
negativeDiaglonalSum += orderedPoints.get(i).y * orderedPoints.get(0).x;
} else {
negativeDiaglonalSum += orderedPoints.get(i).y * orderedPoints.get(i+1).x;
}
}

//subtract second sum from first, divide by 2
double area = Math.abs((positiveDiagonalSum - negativeDiaglonalSum) / 2.0);

return area;
}
```