// trapezoide.java  compile    javac -cp . trapezoide.java
//                  execute    java  -cp . trapezoide

public class trapezoide
{
  public trapezoide()
  {
    double xmin = 1.0;
    double xmax = 2.0;
    int n = 10;
    double area = 0.0;
    
    System.out.println("trapezoide.java running");
    area = trap_int(xmin, xmax, n); // f(x) available
    System.out.println("trap_int area under x*x from "+xmin+
		       " to "+xmax+" = "+area);
    System.out.println("trapezoide.java finished");
  }
  
  double f(double x) // function to be integrated
  {
     return x*x;
  }

  // double trap_int((*f)(double x), double xmin, double xmax, int nstep)

  double trap_int(double xmin, double xmax, int nstep)
  {               // integrate f(x) from xmin to xmax
    double area, h, x;
    area=(f(xmin)+f(xmax))/2.0;
    h = (xmax-xmin)/(double)nstep;
    for(int i=1; i<nstep; i++)
    {
      x = xmin+(double)i*h;
      area = area + f(x);
    }
    return area*h;   // trapezoidal method
  }

  public static void main (String[] args) // "main" required
  {
    new trapezoide(); // construct and execute
  }
} // end trapezoide.java