-
8/3/2019 Computer Notes - Date Class
1/25
Date Class
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
2/25
Date Classclass Date{int day, month, year;
static Date defaultDate;
public:
void SetDay(int aDay);int GetDay() const;
void AddDay(int x);
static void SetDefaultDate(
int aDay,int aMonth, int aYear);
-
8/3/2019 Computer Notes - Date Class
3/25
Date Class...private:
bool IsLeapYear();};
int main(){
Date aDate;
aDate.IsLeapYear(); //Error
return 0;
}
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
4/25
Creating SpecialDate Class
Special Date
Date Special Date
AddSpecialYear...
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
5/25
Creating SpecialDate Classclass SpecialDate: public Date{
public:void AddSpecialYear(int i){
...
if(day == 29 && month == 2&&
!IsLeapyear(year+i)){ //ERROR!
...
}
}
};
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
6/25
Modify Access Specifier We can modify access specifier
IsLeapYear from private to public
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
7/25
Modified Date Classclass Date{
public:
...
bool IsLeapYear();
};
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
8/25
Modified AddSpecialYearvoid SpecialDate :: AddSpecialYear
(int i){...
if(day == 29 && month == 2&&
!IsLeapyear(year+i)){
...}
}http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
9/25
Protected members Protected members can not be
accessed outside the class Protected members of base class
become protected member ofderived class in Public
inheritance
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
10/25
Modified Date Classclass Date{
protected:bool IsLeapYear();
};
int main(){
Date aDate;
aDate.IsLeapYear(); //Error
return 0;
}
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
11/25
Modified AddSpecialYearvoid SpecialDate :: AddSpecialYear
(int i){...
if(day == 29 && month == 2&&
!IsLeapyear(year+i)){
...
}
}http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
12/25
Disadvantages
Breaks encapsulation
The protected member is part of base
classs implementation as well as
derived classs implementation
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
13/25
IS A Relationship Public inheritance models the IS A
relationship
Derived object IS A kind of base
object
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
14/25
Exampleclass Person {char * name;
public: ...const char * GetName();
};
class Student: public Person{
int rollNo;
public: ...int GetRollNo();
};http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
15/25
Exampleint main()
{
Student sobj;
cout
-
8/3/2019 Computer Notes - Date Class
16/25
IS A Relationship The base class pointer can point
towards an object of derived class
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
17/25
int main(){
Person * pPtr = 0;Student s;
pPtr = &s;cout GetName();
return 0;
}
Example
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
18/25
ExamplepPtr = &s;
derived member1
derived member2...
base member1
base member2
...
spPtr
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
19/25
int main(){
Person * pPtr = 0;Student s;
pPtr = &s;//Error
cout GetRollNo();
return 0;
}
Example
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
20/25
Static Type The type that is used to declare a
reference or pointer is called itsstatic type
The static type of pPtr is Person
The static type of s is Student
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
21/25
Member Access The access to members is
determined by static type The static type of pPtr is Person
Following call is erroneous
pPtr->GetRollNo();
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
22/25
IS A Relationship We can use a reference of derived
object where the reference of baseobject is required
http://ecomputernotes.com
-
8/3/2019 Computer Notes - Date Class
23/25
Exampleint main(){
Person p;Student s;
Person & refp = s;
cout
-
8/3/2019 Computer Notes - Date Class
24/25
Examplevoid Play(const Person& p){cout
-
8/3/2019 Computer Notes - Date Class
25/25
Exampleint main(){
Person p;Student s;
Play(p);Play(s);
return 0;
}http://ecomputernotes.com
