double[][] points = {
                {0.0, 1.0},
                {0.5, 2.0},
                {1.0, 4.0},
                {0.5, 5.0},
                {2.0, 0.0}
        };

        int last = points.length - 1;
        int i;
        double inner = 0.0, outer = 0.0;

        for(i = 0; i < last; i++){
                outer += (points[i][0] * points[i + 1][1]) + (points[last][0] * points[0][1]);
                inner += (points[i + 1][0] * points[i][1]) + (points[0][0] * points[last][1]);
        }

        System.out.println("outer: " + String.valueOf(outer));
        System.out.println("inner: " + String.valueOf(inner));
        System.out.println("area: " + String.valueOf(outer - inner));