Inheritance Lecture 9

2. InheritanceLecture 9 Course Name: High Level Programming Language Year : 2010

3. Learning Outcomes At the end of this lecture, students are capable of: Understanding the concept of Inheritance in C++ programming.

4. Outline Materi • Introduction to the conceptual of Inheritance • Declaration of Derived Class • Types access of Derived Class • Single Inheritance

5. Introduction to the conceptual of Inheritance • The mechanism by which one class can inherit the properties of another. • It allows a hierarchy of classes to be built, moving from the most general to the most specific.

6. Forms of Class Hierarcy Single Inheritance Multiple Inheritance

7. Class Hierarchy • In the design of class hierarchy, based class is a class that has the most common properties or the properties that are needed by its derived class. • While specific behaviors are belonged to its derived classes, where those specific behaviors are used to improve the based class.

8. C++ Syntax for Inheritance • class Nama_Turunan : jenis_akses Nama_Induk • { <Anggota_klas> } • Contoh : • class Barang • { protected: int A; • }; • class Meja : public Barang • { protected: int B; • }; Nama_Turunan Jenis_akses

9. Example: Base Class class base { int x; public: void setx(int n) { x = n; } void showx() { cout << x << ‘\n’ } };

10. Example: Derived Class // Inherit as public class derived : public base { int y; public: void sety(int n) { y = n; } void showy() { cout << y << ‘\n’;} };

11. Access member of Base class from Derived class • Member of based class can be accessed by its derivative class, if access-member of the based class is public or protected. • Protected member of based class can be accessed by its derived classes, as it is declared inside its derived classes. • Protected member from a class can not be accessed by other functions or classes in a program, that are not derived from the based class.

12. Access Type of Derived Class • class Nama_Turunan : jenis_akses Nama_Induk { <Anggota_klas> } • Access type from the above derived class can be of typepublic/protected/private.

13. #include <iostream.h> #include <stdio.h> #include <conio.h> class Mahasiswa {private: char NIM[11], Nama[40]; public: void Masuk_Mhs () { cout << “Masukkan NIM : “; cin >> NIM; cout << “Masukkan Nama : “; gets( Nama ); } void Tampil_Mhs () {cout << “NIM = “ << NIM << endl; cout << “Nama = “ << Nama < endl; } }; class Mata_Kuliah : public Mahasiswa {protected: char Kd_Kuliah[6], Nm_MataKuliah[30]; public: void Masuk_Kuliah () { cout << “Masukkan Kode Kuliah : “; cin >> Kd_Kuliah; cout << “Masukkan Nama Mata Kuliah : “; gets( Nm_MataKuliah ); } Program1 - Single Inheritance void Tampil_Kuliah () { cout << “Kode Kuliah : “ << Kd_Kuliah << endl; cout << “Nama Mata Kuliah : “ << Nm_MataKuliah << endl; } }; void main( ) { Mata_Kuliah M1; M1.Masuk_Mhs(); M1.Masuk_Kuliah(); M1.Tampil_Mhs(); M1.Tampil_Kuliah(); getch(); }

14. #include <iostream.h> #include <stdio.h> #include <conio.h> class Pegawai { protected: char NIP[10], Nama[30]; public: void Masuk_Data () { cout << “Masukkan Nomor Induk Pegawai : “; cin >> NIP; cout << “Masukkan Nama Pegawai : “; cin >> Nama; } void Tampil_Data () { cout << “Nomor Induk Pegawai = “ << NIP << endl; cout << “Nama Pegawai = “ << Nama << endl; } }; Program 2 - single Inheritance class Manager : public Pegawai {protected: char Titel[20], Telpon[20]; public: void Masuk_Data () { Pegawai :: Masuk_Data(); cout << “Masukkan titel dari manager : “; cin >> Titel; cout<< “Masukkan No Telpon : “; cin >> Telpon; } void Tampil_Data () { Pegawai :: Tampil_Data(); cout << “Titel dari manager : “ << Titel << endl; cout << “No Telpon manager : “ << Telpon << endl; } };

15. class Peneliti : public Pegawai {protected: int Publikasi; public: void Masuk_Data () { Pegawai :: Masuk_Data(); cout << “Masukkan No Publikasi : “; cin >> Publikasi; } void Tampil_Data () { Pegawai :: Tampil_Data(); cout << “No Publikasi Peneliti : “ << Publikasi << endl; } }; class Satpam : public Pegawai { }; void main () { Manager m1, m2; Peneliti p1; Satpam s1; Program2 (Cont.) // Bagian Entry data cout << “\nMasukkan data untuk manager 1 : “; m1.Masuk_Data(); cout << “\nMasukkan data untuk manager 2 : “; m2.Masuk_Data(); cout << “\nMasukkan data untuk peneliti 1 : “; p1.Masuk_Data(); cout << “\nMasukkan data untuk satpam 1 : “; s1.Masuk_Data(); // Bagian Display data cout << “\nData dari manager 1 : “; m1.Tampil_Data(); cout << “\nData dari manager 2 : “; m2.Tampil_Data(); cout << “\nData dari peneliti 1 : “; p1.Tampil_Data(); cout << “\nData dari satpam 1 : “; s1.Tampil_Data(); getch(); }

16. Constructor and Destructor • It is possible for both the base class and the derived class to have constructor and/or destructor functions. • The constructor functions are executed in order of derivation. • i.e.the base class constructor is executed first. • The destructor functions are executed in reverse order.

17. Passing arguments What if the constructor functions of both the base class and derived class take arguments? • Pass all necessary arguments to the derived class’s constructor. • Then pass the appropriate arguments along to the base class.

18. Example: Constructor of base class base { int i; public: base(int n) { cout << “constructing base \n”; i = n; } ~base() { cout << “destructing base \n”; } };

19. Example: Constructor of derived class derived : public base { int j; public: derived (int n, int m) : base (m) { cout << “constructing derived\n”; j = n; } ~derived() { cout << “destructing derived\n”;} };

20. Example: main() int main() { derived o(10,20); return 0; } constructing base constructing derived destructing derived destructing base

21. Multiple Inheritance • Type 1: base 1 derived 1 derived 2

22. Multiple Inheritance • Type 2: base 1 base 2 derived

23. Example: Type 2 // Create first base class class B1 { int a; public: B1(int x) { a = x; } int geta() { return a; } };

24. Example: Type 2 // Create second base class class B2 { int b; public: B2(int x) { b = x; } int getb() { return b; } };

25. Example: Type 2 // Directly inherit two base classes. class D : public B1, public B2 { int c; public: D(int x, int y, int z) : B1(z), B2(y) { c = x; } void show() { cout << geta() << getb() << c;} } ;

26. Potential Problem • Base is inherited twice by Derived 3! Base Base Derived 2 Derived 1 Derived 3

27. Virtual Base Class • To resolve this problem, virtual base class can be used. class base { public: int i; };

28. Virtual Base Class // Inherit base as virtual class D1 : virtual public base { public: int j; }; class D2 : virtual public base { public: int k; };

29. Virtual Base Class /* Here, D3 inherits both D1 and D2. However, only one copy of base is present */ class D3 : public D1, public D2 { public: int product () { return i * j * k; } };

30. Pointers to Derived Classes • A pointer declared as a pointer to base class can also be used to point to any class derived from that base. • However, only those members of the derived object that were inherited from the base can be accessed.

31. Example base *p; // base class pointer base B_obj; derived D_obj; p = &B_obj; // p can point to base object p = &D_obj; // p can also point to derived // object

32. Conclusions • Inheritance promotes the reusability of coding. • Member-access specifier relates base class with its derived class. • The constructor functions are executed in order of derivation. • Virtual Base Class is a way to solve problem of multiple base class being derived in multiple inheritance.

33. Topic For Next Week • Polymorphism • Assignment: In order to answer the following questions below, please read C++ Begineer’s Guide CH10.pdf. Questions are taken from page 37! • What is a virtual function? • Why are virtual functions important? • When an overridden virtual function is called through a base class pointer, which version of the function is executed?