public class Trapezoid {
    public static double trapzd(MathFunction func, double a, double b, int n) {
        if (n==1) {
            s= 0.5*(b-a)*(func.f(a)+func.f(b));
            return s; }
        else {
            int it= 1;
            for (int j= 0; j < n-2; j++)
                it *= 2;              // Subdivisions
            double tnm= it;
            double delta= (b-a)/tnm;  // Spacing of points to be added
            double x= a+0.5*delta;
            double sum= 0.0;
            for (int j= 0; j < it; j++) {
                sum += func.f(x);
                x+= delta; }
            s= 0.5*(s+(b-a)*sum/tnm);
            return s;
        }
    }
    private static double s;    // Holds current estimate of integral. Do only 1 at a time.
}