//
// example of use of java.net.* classes and serialization:  
//      set up client/server interaction in which client sends request 
//      object to server for processing and server returns result.
// this file defines classes for request objects; RequestServer.java
//      and RequestClient.java contain the programs for the server and
//      client.
// example adapted from one in chapter 11 of _Exploring Java_ by
//      Niemeyer & Peck.
//

//
// the Request class is the base class for requests to be sent from
//      the client to the server.  
// implement Serializable so our objects can be serialized for
//      transmission over the network.
//
abstract class Request implements java.io.Serializable {

        // subclasses implement this method to define what service
        //      they want the server to perform.  return type is
        //      Object to permit returning any type.
        abstract public Object serviceRequest() ;

        // subclasses can override this method.
        public String toString() {
                return "Request" ;
        }
}

//
// a ShowLocalTime object represents a request that the server
//      create and format a Date object showing the local time/date
//      at the server.  what is returned is a string showing
//      local time/date.
//
class ShowLocalTime extends Request {

        public Object serviceRequest() {
                System.out.println("servicing ShowLocalTime") ;
                return new java.util.Date().toString() ;
        }

        public String toString() {
                return "ShowLocalTime" ;
        }
}

//
// a FindRealRoots object represents a request that the server
//      calculate the real roots of the quadratic equation
//      a*x*x + b*x + c = 0.  what is returned is an array
//      containing the 0, 1, or 2 real roots.
// since such a request must include some data (values for
//      a, b, and c), we define some instance variables
//      and provide an appropriate constructor.
//
class FindRealRoots extends Request {

        double a, b, c ;

        FindRealRoots(double a, double b, double c) {
                this.a = a ; this.b = b ; this.c = c ;
        }

        public Object serviceRequest() {
                System.out.println("servicing FindRealRoots") ;
                double discrim = b*b - 4*a*c ;
                double[] roots ;
                if (discrim < 0) {
                        roots = new double[0] ;
                }
                else if (discrim == 0) {
                        roots = new double[1] ;
                        roots[0] = (-b)/(2*a) ;
                }
                else {
                        roots = new double[2] ;
                        roots[0] = (-b + Math.sqrt(discrim))/(2*a) ;
                        roots[1] = (-b - Math.sqrt(discrim))/(2*a) ;
                }
                return roots ;
        }

        public String toString() {
                return "FindRealRoots (" + 
                        a + ", " + b + ", " + c + ")" ;
        }
}