Object Oriented Programming Using C CLASS 5 1 Object Composition Object composition occurs when a class contains an instance of another class Creates a has a relationship between classes 2 Composition example not in textbook A class can contain an object of another class class Date class Employee public public methods methods private private data data char lastName 25 char firstName 25 Date birthdate Date hiredate 3 Date class 4 DATE1 H ifndef DATE1 H define DATE1 H class Date public Date int 1 int 1 int 1900 default constructor void print const Date private int month 1 12 int day 1 31 based on month int year any year int checkDay int endif 5 Date Date int mn int dy int yr if mn 0 mn 12 month mn else month 1 cout Month 1 mn invalid Set to month 1 endl year yr could also check day checkDay dy validate the day cout Date object constructor for date print cout endl 6 int Date checkDay int testDay static int daysPerMonth 13 0 31 28 31 30 31 30 31 31 30 31 30 31 if testDay 0 testDay daysPerMonth month return testDay if month 2 testDay 29 year 400 0 year 4 0 year 100 0 return testDay cout Day testDay invalid Set to day 1 endl return 1 7 Print Date object in form month day year void Date print const cout month day year Date Date cout Date object destructor for date print cout endl 8 Employee class 9 emply1 h ifndef EMPLY1 H define EMPLY1 H include date1 h class Employee public Employee char char int int int int int int void print const Employee private char firstName 25 char lastName 25 const Date birthDate const Date hireDate 10 endif Member function definitions for Employee class include iostream using namespace std include cstring include emply1 h include date1 h 11 Employee Employee char fname char lname int bmonth int bday int byear int hmonth int hday int hyear birthDate bmonth bday byear hireDate hmonth hday hyear body of constructor 12 Employee Employee char fname char lname int bmonth int bday int byear int hmonth int hday int hyear birthDate bmonth bday byear hireDate hmonth hday hyear constructor of date class called twice once for the birthDate object once for the hireDate object body of constructor 13 int length strlen fname length length 25 length 24 strncpy firstName fname length firstName length 0 length strlen lname length length 25 length 24 strncpy lastName lname length lastName length 0 cout Employee object constructor firstName lastName endl 14 void Employee print const cout lastName firstName nHired hireDate print cout Birth date birthDate print cout endl Employee Employee cout Employee object destructor lastName firstName endl P 466 15 include iostream using namespace std Parameters to the Employee constructor include emply1 h int main Employee e Bob Jones 7 24 1949 3 12 1988 e print Date d 14 35 1994 cout endl return 0 For the Birthdate For the Hiredate object object 16 Abstract Data Types Modularity Keeps the complexity of a large program manageable by systematically controlling the interaction of its components Isolates errors Eliminates redundancies 17 Abstract Data Types Modularity Continued A modular program is Easier to write Easier to read Easier to modify 18 Abstract Data Types Functional abstraction Separates the purpose and use of a module from its implementation A module s specifications should Detail how the module behaves Be independent of the module s implementation 19 Abstract Data Types Information hiding Hides certain implementation details within a module Makes these details inaccessible from outside the module 20 Abstract Data Types Typical operations on data Add data to a data collection Remove data from a data collection Ask questions about the data in a data collection 21 Abstract Data Types Data abstraction Asks you to think what you can do to a collection of data independently of how you do it Allows you to develop each data structure in relative isolation from the rest of the solution A natural extension of functional abstraction 22 Abstract Data Types Abstract data type ADT An ADT is composed of A collection of data A set of operations on that data Specifications of an ADT indicate What the ADT operations do not how to implement them Implementation of an ADT Includes choosing a particular data structure 23 Abstract Data Types Figure 3 4 A wall of ADT operations isolates a data structure from the program that uses it 24 Object Oriented Analysis and Design Object oriented design OOD Expresses an understanding of a solution that fulfills the requirements discovered during OOA Describes a solution in terms of Software objects The collaborations of these objects with one another Objects collaborate when they send messages call each other s operations Collaborations should be meaningful and minimal Creates one or more models of a solution Some emphasize interactions among objects Others emphasize relationships among objects 1 25 Applying the UML to OOA D Unified Modeling Language UML A tool for exploration and communication during the design of a solution Models a problem domain in terms of objects independently of a programming language Visually represents object oriented solutions as diagrams Its visual nature is an advantage since we are visual creatures Enables members of a programming team to communicate visually with one another and gain a common understanding of the system being built 1 26 Applying the UML to OOA D UML use case for OOA A set of textual scenarios stories of the solution Each scenario describes the system s behavior under certain circumstances from the perspective of the user Focus on the responsibilities of the system to meeting a user s goals Main success scenario happy path interaction between user and system when all goes well Alternate scenarios interaction between user and system under exceptional circumstances Find noteworthy objects attributes and associations within the scenarios 1 27 Applying the UML to OOA D An example of a main success scenario Customer asks to withdraw money from a bank account Bank identifies and authenticates customer Bank gets account type account number and withdrawal amount from customer Bank verifies that account balance is greater than withdrawal amount Bank generates receipt for the transaction Bank counts out the correct amount of money for customer Customer leaves bank 1 28 Applying the UML to OOA D An example of an alternate scenario 1 29 Customer asks to withdraw money from a bank account Bank identifies but fails to authenticate customer Bank refuses to process the customer s