Inheritance: The Fundamental Functions Lecture 24 Mon, Mar 26, 2007 2/17/2019 Inheritance

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. 2/17/2019 Inheritance

Inheritance of Constructors Suppose we create a List class and then derive an ArrayList class and a LinkedList class from it. List ArrayList LinkedList 2/17/2019 Inheritance

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;} 2/17/2019 Inheritance

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. 2/17/2019 Inheritance

Inheritance of Constructors Which List constructor will it call? Unless we specify otherwise, it will call the default List constructor. 2/17/2019 Inheritance

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} 2/17/2019 Inheritance

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; 2/17/2019 Inheritance

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. 2/17/2019 Inheritance

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. 2/17/2019 Inheritance

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; } 2/17/2019 Inheritance

Inheritance of the Assignment Operator See the tip about the assignment operator. 2/17/2019 Inheritance

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. 2/17/2019 Inheritance

Inheritance of the Assignment Operator ArrayListwPos& operator=(const ArrayListwPos& list) { if (this != &list) ArrayList::operator=(list); currPos = list.currPos; } return *this; 2/17/2019 Inheritance

Example: Inheritance Header files person.h man.h woman.h father.h mother.h marriedman.h marriedwoman.h 2/17/2019 Inheritance

Example: Inheritance Programs DefaultPeople.cpp FamilyTree.cpp TheFirstFamily.cpp ChangingPlaces.cpp 2/17/2019 Inheritance