Class (Inheritance) SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong

Transcription

1 Class (Inheritance) Prof. Jinkyu Jeong TA -- Minwoo Ahn TA -- Donghyun Kim Computer Systems Laboratory Sungkyunkwan University SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong

2 Object Oriented Programming Vehicle class Inheritance? SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong 2

3 Inheritance Concept Rectangle Polygon Triangle class Rectangle{ private: int numvertices; float *xcoord, *ycoord; void set(float *x, float *y, int nv); float area(); class Polygon{ class Triangle{ private: private: int numvertices; int numvertices; float *xcoord, *ycoord; float *xcoord, *ycoord; void set(float *x, float *y, int nv); void set(float *x, float *y, int nv); float area(); SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong 3

4 Inheritance Concept Rectangle Polygon Triangle class Polygon{ protected: int numvertices; float *xcoord, float *ycoord; void set(float *x, float *y, int nv); class Rectangle{ protected: class Rectangle : public Polygon{ int numvertices; float *xcoord, float *ycoord; float area(); void set(float *x, float *y, int nv); float area(); SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 4

5 Inheritance Concept Rectangle Polygon Triangle class Polygon{ protected: int numvertices; float *xcoord, float *ycoord; void set(float *x, float *y, int nv); class Triangle{ protected: class Triangle : public Polygon{ int numvertices; float *xcoord, float *ycoord; float area(); void set(float *x, float *y, int nv); float area(); SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 5

6 Inheritance Concept Circle x y r Point 3D-Point x y z x y class Point{ protected: int x, y; void set (int a, int b); class Circle : public Point{ private: double r; class 3D-Point: public Point{ private: int z; SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 6

7 Inheritance Concept Augmenting the original class Polygon Point Rectangle Triangle Circle 3D-Point Specializing the original class ComplexNumber real imag real RealNumber ImaginaryNumber imag SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong 7

8 Why Inheritance? Inheritance is a mechanism for building class types from existing class types defining new class types to be a specialization augmentation of existing types SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 8

9 Define a Class Hierarchy Syntax: class DerivedClassName : access-level BaseClassName where access-level specifies the type of derivation private by default, or public Any class can serve as a base class Thus a derived class can also be a base class SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 9

10 Class Derivation Point 3D-Point Sphere class 3D-Point : public Point{ private: double z; class Point{ protected: int x, y; void set (int a, int b); class Sphere : public 3D-Point{ private: double r; Point is the base class of 3D-Point, while 3D-Point is the base class of Sphere SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 10

11 What to Inherit? In principle, every member of a base class is inherited by a derived class just with different access permission SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 11

12 derive from Access Control Over the Members base class/ superclass/ parent class members goes to derived class/ subclass/ child class Two levels of access control over class members class definition inheritance type class Point{ protected: int x, y; void set(int a, int b); class Circle : public Point{ SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 12

13 Access Rights of Derived Classes Type of Inheritance Access Control for Members private protected public private protected private protected protected public private protected public The type of inheritance defines the access level for the members of derived class that are inherited from the base class SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 13

14 Class Derivation class mother{ protected: int mproc; int mpubl; private: int mpriv; private/protected/public class daughter : mother{ private: double dpriv; void mfoo dfoo ((); ); class granddaughter : public daughter { private: double gpriv; void gfoo ( ); int main() { /*.*/ } void daughter :: dfoo ( ){ mpriv = 10; //error mproc = 20; SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 14

15 Access Rights Examples Type of inheritance: private num1, num2, num3 are inaccessible SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong 15

16 Access Rights Examples Type of inheritance: protected num1, num2, num3 are inaccessible SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong 16

17 Access Rights Examples Type of inheritance: public num1, num2 are inaccessible num3 is accessible SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong 17

18 What to Inherit? In principle, every member of a base class is inherited by a derived class just with different access permission However, there are exceptions for constructor and destructor operator=() member friends Since all these functions are class-specific SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 18

19 Constructor Rules for Derived Classes The default constructor and the destructor of the base class are always called when a new object of a derived class is created or destroyed. class A { A ( ) {cout<< A:default <<endl;} A (int a) {cout<< A:parameter <<endl;} class B : public A { B (int a) {cout<< B <<endl;} B test(1); output: A:default B SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 19

20 Constructor Rules for Derived Classes You can also specify an constructor of the base class other than the default constructor DerivedClassCon ( derivedclass args ) : BaseClassCon ( baseclass args ) { DerivedClass constructor body } class A { A ( ) {cout<< A:default <<endl;} A (int a) {cout<< A:parameter <<endl;} C test(1); output: class C : public A { C (int a) : A(a) {cout<< C <<endl;} A:parameter C SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 20

21 Define its Own Members The derived class can also define its own members, in addition to the members inherited from the base class Point x y class Point{ protected: int x, y; void set(int a, int b); x y r Circle class Circle : public Point{ private: double r; void set_r(double c); class Circle{ protected: int x, y; private: double r; void set(int a, int b); void set_r(double c); SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 21

22 Even More A derived class can override methods defined in its parent class. With overriding, the method in the subclass has the identical signature to the method in the base class. a subclass implements its own version of a base class method. class A { protected: int x, y; void print () {cout<< From A <<endl;} class B : public A { void print () {cout<< From B <<endl;} SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 22

23 Even More Multiple Inheritance SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong 23

24 Access Method class Point{ protected: int x, y; void set(int a, int b) {x=a; y=b;} void foo (); void print(); class Circle : public Point{ private: double r; void set (int a, int b, double c) { Point :: set(a, b); //same name function call r = c; } void print(); Point A; A.set(30,50); // from base class Point A.print(); // from base class Point Circle C; C.set(10,10,100); // from class Circle C.foo (); // from base class Point C.print(); // from class Circle SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 24

25 [Lab Practice #1] Calculate Average Class : student Variables(private) : float math, science, english, korean, average Methods(public): getter/setter for each member variables Class : school Variables(private) : student students[10] Methods(public) : void calc_avg() void print_result() Class : university Variables(private) : int m_credit, s_credit, e_credit, k_credit Methods(public) : void calc_avg() SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 25

26 Class Hierarchy School Type of inheritance: public University Object Object UniversityA UniversityB SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong 26

27 Sample Input/Output <score> students[i].math = i * students[i].science = i * students[i].english = i * students[i].korean = i * <main> int main(){ universitya univ_a(3, 4, 1, 2); universityb univ_b(2, 1, 4, 3); } <output> University A student 0, math : 20, science : 30, english : 40, korean : 50, average : 32. University B student 0, math : 20, science : 30, english : 40, korean : 50, average : 38. SSE2034: System Software Experiment 3, Fall 2018, Jinkyu Jeong (jinkyu@skku.edu) 27