Object-Oriented Design

Object-Oriented Design Lesson #13 Note: CIS 601 notes were originally developed by H. Zhu for NJIT DL Program. The notes were subsequently revised by M. Deek

Activities in Software Development • Problem Analysis • Solution Design • Coding • Documenting • Testing • Maintenance

Strategy • One basic way to deal with complexity: Divide and Conquer. • Systems can be divided into modules (Objects or Classes). • The challenge is to ensure effective communication between different parts of the program without destroying the divisions.

Objectives • We are concerned with producing software that satisfies user requirements. • The primary means to do so is to produce software with a clean internal structure.

The Tasks of OO Design We need to specify: • The needed classes • The public interface • The protected interface

The Need for a Clean Internal Structure To simplify: • Testing • Porting • Maintenance • Extension • Re-organization • Understanding

Characteristics of Successful Software It has an extended life where it might be: • worked on by a succession of programmers and designers • ported to new hardware • adapted to unanticipated uses

The Development Cycle • Create an overall design • Find standard components and then customize the components for this design. • Create new standard components and then customize the components for this design. • Assemble design.

Design for Change • The system must be designed to remain as simple as possible under a sequence of changes. • Aim for: • flexibility • extensibility • portability • OOD can support the above.

Design Steps of OOD • Find the Concepts/Classes and their fundamental relationships. • Refine the Classes by specifying the sets of Operations on them • classify these operations: constructors, destructors, etc. • consider minimalism, completeness, and convenience

Design Steps • Refine the classes by specifying their dependencies on other classes: • Inheritance • Use dependencies • Specify the interfaces for the classes: • separate functions into public and protected operations • specify the exact type of the operations on the classes.

Finding Classes • Good design must capture and model some aspects of reality. • Look at the application rather than the abstractions. • Usually nouns correspond to classes and verbs represent functions.

Example • When ordering new videotapes from a supplier, the store manager creates a purchase order, fills in the date, the supplier’s name , address, and enters a list ofvideotapes to be ordered. The purchase order is added to a permanent list of purchases. When one or more video tapes are received from a supplier, a clerk locates the original purchase order and makes a record of each tape that was received. A record of the videotape is then added to the store’s inventory. When all tapes listed on a particular purchase order have been received, the manager sends a payment to the supplier and the purchase order is given a completion date.

Specifying operations • Consider how an object of the class is constructed, copied, and destroyed. • Define the minimal set of operations required by the concept the class is representing. • Consider which operations could be added for notational convenience and include only important ones.

Specifying Operations • Consider which operations are to be virtual. • Consider what commonality of naming and functionality can be achieved across all the classes of the component.

Operations on a Class • Foundation: • Constructors, destructors, and copy operators • Selectors: • Operations that do not modify the state of an object. • Modifiers: • Operations that modify the state of an object.

Operations on a Class • Conversion Operators: • Operations that produce an object of another type based on the value (state) of the object to which they are applied. • Iterators: • Operations that process data members containing collections of objects.

Specifying Dependencies • The key dependencies to consider in the context of design are inheritance and use relationships. • Overuse can lead to inefficient and incomprehensible designs.

Specifying Interfaces • Private functions are not considered at this stage. • The interface should be implementation independent (more than one implementation should be possible). • All operators in a class should support the same level of abstraction.

Reorganizing the Class Hierarchy • Typically, initial organization of classes may not be adequate and therefore, may have to be reorganize to improve the design and/or implementation. • The two most common reorganizations of a class hierarchy are: • factoring of two classes into a new class. • splitting a class into two new ones.

Use of Models • Whenever possible, design and programming should be based on previous work. • This allows the designer to focus on a the important issues at any given time.

Experimentation and Analysis • Prototyping is frequently used for experimenting. • Different aspects of a system may be prototyped independently, such as the graphical user interface. • Analysis of a design and/or implementation can be an important source of insight.

Example:Doctor’s office scheduling • Specification: • The program allows to schedule appointments for patients. • The office has multiple doctors, each with a daily schedule divided into 15-minute appointment slots beginning from 8:00am to 6:00pm. • We also want to print out separate daily schedules for each doctor, listing the time and patient name of each appointment. • All output directed to the screen, except for the doctors’ schedules, which will be written to a file for later printing. • For simplicity: Each doctor has only one appointment day.

Analysis • Finding classes: • Doctor • Patient • DailySchedule • Appointment • Scheduler (Interface to the user)

Scenario of the process • Scheduler requests the patient’s name; • Patient chooses a doctor; • Scheduler displays doctor’s schedule, showing available appointment slots; • Patient requests the specific slot; • Scheduler adds the appointment to the doctor’s schedule, and adds the appointment to the patient’s record; • Scheduler confirms the appointment.

Class dependencies Scheduler Fstring(LastName) Patient Doctor Fstring(FirstName) DailySchedule Appointment :composite(contains) :link(requests, send messages)

Operations • Doctor 1. AddToSchedule: Add an appt. to the Dr’s Sch. 2. ShowAppointment:Display the sch • Patient 1.InputName: 2.ChooseDoctor: 3.ChooseTimeSlot: 4.SetAppointment: Schedule an Appt.

Operations • DailySchedule 1.SetAppointment: Add an appt to the sch. 2.IsTimeSlotFree:Find out if a particular slot is available 3.ShowAppointments: Display the schd appt • Appointment 1.Constructor: 2.IsScheduled: Find out if an appt schd for the current Appt • Scheduler 1.ScheduleOneAppointment: p-appt-d 2.ScheduleAllAppointments:input p, request d, update d 3.PrintAllAppointment: print all the schd appt for all Ds

Additional Classes • TimeSlot: • Handles the translation and formatting of appointment times. • FString: • Deals with string data members.

The TimeSlot class class TimeSlot { public: TimeSlot( const unsigned n = 0 ); unsigned AsInteger() const; friend istream & operator >>(istream & inp, TimeSlot & T); friend ostream & operator <<(ostream & os, const TimeSlot & T); private: static unsigned StartHour; static unsigned ApptLen; unsigned intValue; };

The Appointment class class Appointment { public: Appointment(); Appointment ( const TimeSlot & aTime, unsigned docNum, const Patient & P); const FString & GetPatientName() const; const TimeSlot & GetTime() const; int IsScheduled() const; void SetTime( const unsigned n ); friend ostream & operator <<( ostream & os,const Appointment & A ); private: enum { NoDoctor = 9999 }; unsigned doctorNum; TimeSlot timeSlot; FString patientName; };

The Patient class class Patient { public: Patient(); void InputName(); unsigned ChooseDoctor() const; TimeSlot ChooseTimeSlot(const Doctor & D) const; const Appointment & GetAppointment() const; const FString & GetFirstName() const; const FString & GetLastName() const; int IsScheduled() const; void SetAppointment( const Appointment & A ); friend ostream & operator <<( ostream & os, const Patient & P ); private: FString lastName; FString firstName; Appointment nextVisit; };

The DailySchedule class class DailySchedule { public: DailySchedule(); int IsTimeSlotFree( const TimeSlot & T ) const; void SetAppointment( const Appointment & A ); void ShowAppointments( ostream & os ) const; friend ostream & operator <<( ostream & os, const DailySchedule & DS ); private: enum { MaxTimeSlots = 40 }; Appointment appointments[MaxTimeSlots]; };

The Doctor class class Doctor { public: Doctor(); int AddToSchedule( const Appointment & A ); const DailySchedule & GetSchedule() const; void SetId( const unsigned ); void SetLastName( const FString & L ); const FString & GetLastName() const; void ShowAppointments( ostream & ) const; static const FString & GetDoctorName( unsigned index ); static void SetDoctorName(unsigned, const FString & nam); private: unsigned id; FString lastName; DailySchedule schedule; static FString doctorName[NumDoctors]; };

The Scheduler class class Scheduler { public: Scheduler( Doctor * docs ); void PrintAllAppointments( const char * fileName); int ScheduleOneAppointment(); void ScheduleAllAppointments(); private: Doctor * doctors; };

The main Program #include "doctors.h" static Doctor doctorArray[NumDoctors]; int main() { cout << "Doctors Office Scheduling Program\n\n"; Scheduler officeSchedule( doctorArray ); officeSchedule.ScheduleAllAppointments(); officeSchedule.PrintAllAppointments( "appts.txt" ); return 0; }

The Implementation • The Time Slot • h : hour value • sa: the starting appointment time • aph: appointments per hour • m: minute value • al: the appointment length in minutes timeslot = (h-sa)*aph+m/al E.g: timeslot = (12-8)*4+20/15=17 The 17th slot.

The TimeSlot class unsigned TimeSlot::StartHour = 8; unsigned TimeSlot::ApptLen = 15; istream & operator >>( istream & inp, TimeSlot & T ) { char buf[20]; inp.getline( buf, 20 ); // get a line of input istrstream aStream( buf, 20 ); unsigned h, m; char ch; aStream >> dec >> h >> ch >> m; unsigned aph = 60 / TimeSlot::ApptLen; if( h < T.StartHour ) // afternoon hour? h += 12; // add 12 to hours T.intValue = ((h - TimeSlot::StartHour)* aph) + (m / TimeSlot::ApptLen); return inp; }

The TimeSlot class ostream & operator <<( ostream & os, const TimeSlot & T ) { unsigned aph = 60 / T.ApptLen; // 4 = 60 / 15 unsigned h = (T.intValue / aph ) + T.StartHour; // (S / 4) + 8 unsigned m = (T.intValue % aph ) * T.ApptLen; // (S % 4) * 15 char oldfill = os.fill('0'); os << setw(2) << h << ':' << setw(2) << m; os.fill( oldfill ); return os; }

The Appointment class Appointment::Appointment ( const TimeSlot & aTime, unsigned docNum, const Patient & aPatient ) { timeSlot = aTime; doctorNum = docNum; patientName = aPatient.GetLastName(); patientName.Append( ", " ); patientName.Append( aPatient.GetFirstName() ); }

The Appointment class ostream & operator <<( ostream & os, const Appointment & A ) { os << "Dr. " << Doctor::GetDoctorName(A.doctorNum) << ", " << "Time: " << A.timeSlot; return os; }

The Patient class void Patient::InputName() { cout << "Patient's last name: "; cin >> lastName; cout << "Patient's first name: "; cin >> firstName; }

The Patient class unsigned Patient::ChooseDoctor() const { for(unsigned i = 0; i < NumDoctors; i++) cout << i << ": " << Doctor::GetDoctorName(i) << '\n'; unsigned n = 0; int ok = 0; do { cout << "Enter a doctor number: "; cin >> n; cin.ignore(255,'\n'); if( n >= NumDoctors ) cout << "Number out of range!\n"; else ok = 1; } while( !ok ); return n; }

The Patient class TimeSlot Patient::ChooseTimeSlot( const Doctor & D ) const { cout << '\n' << "Daily Schedule of Dr. " << D.GetLastName() << '\n' << "........................................" << '\n' << D.GetSchedule() << '\n' << "Enter a time (format hh:mm): "; TimeSlot aSlot; cin >> aSlot; return aSlot; }

The Patient class ostream & operator <<( ostream & os, const Patient & P ) { os << "Patient " << P.firstName << ' ' << P.lastName << '\n' << "has been scheduled as follows:" << '\n' << P.nextVisit << endl; return os; }

The DailySchedule class DailySchedule::DailySchedule() { for(unsigned i = 0; i < MaxTimeSlots; i++) appointments[i].SetTime( i ); } int DailySchedule::IsTimeSlotFree( const TimeSlot & aTime ) const { unsigned n = aTime.AsInteger(); return !appointments[n].IsScheduled(); } void DailySchedule::SetAppointment( const Appointment & app ) { unsigned n = app.GetTime().AsInteger(); appointments[n] = app; }

The DailySchedule class void DailySchedule::ShowAppointments( ostream & os ) const { for(unsigned i = 0; i < MaxTimeSlots; i++) { if( appointments[i].IsScheduled()) os << appointments[i].GetTime() << " " << appointments[i].GetPatientName() << endl; } }

The DailySchedule class ostream & operator <<( ostream & os, const DailySchedule & DS ) { for(unsigned i = 0; i < DS.MaxTimeSlots; i++) { os << DS.appointments[i].GetTime(); if( DS.appointments[i].IsScheduled()) os << " *** "; else os << " "; if( i % 4 == 3 ) os << '\n'; } return os; }

The Doctor class FString Doctor::doctorName[NumDoctors]; //Static member. Doctor::Doctor() { id = 0;} int Doctor::AddToSchedule( const Appointment & app ) { if( schedule.IsTimeSlotFree( app.GetTime())) { schedule.SetAppointment( app ); return 1; } return 0; }

The Doctor class void Doctor::ShowAppointments( ostream & os ) const { os << "Appointments for Dr. " << lastName << '\n' << ".................................." << '\n'; schedule.ShowAppointments( os ); os << endl; }//cis601source/chap5/doctors/

Object-Oriented Design