1. Inheritance: The Fundamental Functions
Lecture 24
Mon, Mar 26, 2007
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Inheritance

2. Inheritance of Constructors
A derived-class constructor will automatically invoke the base-class default constructor, unless instructed otherwise.
The base-class constructor is invoked before the derived-class constructor is executed.
The derived-class constructor may invoke a specific base-class constructor.
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Inheritance

3. Inheritance of Constructors
Suppose we create a List class and then derive an ArrayList class and a LinkedList class from it.
List
ArrayList
LinkedList
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Inheritance

4. Inheritance of Constructors
Since ArrayList and LinkedList have mSize in common, we could put mSize in the List class.
class List
{int mSize;}
class ArrayList
{int* element;}
class LinkedList
{Node* head;}
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Inheritance

5. Inheritance of Constructors
When we construct an ArrayList, what happens?
The ArrayList constructor will first call a List constructor which will initialize mSize. Then it will initialize element.
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6. Inheritance of Constructors
Which List constructor will it call?
Unless we specify otherwise, it will call the default List constructor.
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7. Invoking the Base Class Constructor
How do we specify a different constructor?
We do it through an initializer.
ArrayList(parameters) : List(parameters)
{body of the ArrayList constructor}
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8. Invoking the Base Class Constructor
ArrayList(int sz, int value) : List(sz) {
if (mSize == 0)
element = NULL;
else
element = new int[mSize];
for (int i = 0; i < mSize; i++)
element[i] = value; }
return;
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Inheritance

9. Inheritance of Destructors
The derived-class destructor automatically invokes the base-class destructor.
The base-class destructor is invoked after the derived-class destructor is executed.
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Inheritance

10. Inheritance of the Assignment Operator
The automatic assignment operator invokes the assignment operator for the base class.
A programmer-defined assignment operator must copy the base-class members.
This is a problem if the base-class members are private.
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Inheritance

11. Inheritance of the Assignment Operator
One can use the scope operator :: to invoke the assignment operator of the base class.
class A {private: int a;};
class B : class A {private: int b;};
B& B::operator=(const B& x) {
a = x.a // Illegal
A::operator=(x); // Legal
b = x.b; }
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Inheritance

12. Inheritance of the Assignment Operator
See the tip about the assignment operator.
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Inheritance

13. Inheritance of the Assignment Operator
Suppose we create a class ArrayListwPos, which is an ArrayList that keeps track of a current position.
ArrayListwPos has one additional data member
int currPos – the current position in the list.
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Inheritance

14. Inheritance of the Assignment Operator
ArrayListwPos& operator=(const ArrayListwPos& list) {
if (this != &list)
ArrayList::operator=(list);
currPos = list.currPos; }
return *this;
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15. Example: Inheritance Header files person.h man.h woman.h father.h
mother.h
marriedman.h
marriedwoman.h
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16. Example: Inheritance Programs DefaultPeople.cpp FamilyTree.cpp
TheFirstFamily.cpp
ChangingPlaces.cpp
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Inheritance