Lab 13-1: 異質容器, 虛擬函式, 與多型

    class Student
    {
    public:
        Student(const char *name, const char *ID, 
                const char *phone, const char *department);
        ~Student();
        void display(ostream &os) const;
        bool IDEquals(const char *id) const;
        bool ofTheSameDepartment(Student &student2) const;
    private:
        char *m_name;
        char *m_ID;
        char *m_phone;
        char *m_department;
    };

在嘗試對 Student 類別進行修改, 以及設計繼承的架構之前, 我們可以先來看一下預期的使用方法

    #include <iostream>
    #include <fstream>
    using namespace std;
    
    #include "UndergraduateStudent.h"
    #include "GraduateStudent.h"
    #include "ForeignGraduateStudent.h"
    #include "LoggedStudentList.h"
    #include "StudentListIterator.h"
    
    void main()
    {
        ofstream logfile("main2.log");
        LoggedStudentList sList(logfile);
        sList.appendEntry(new UndergraduateStudent("Mary Chen", "111111111", 
                                      "0933111111", 
                                      "Business",
                                      "John Viega"));
        sList.appendEntry(new UndergraduateStudent("John Wang", "222222222", 
                                      "0928222222", 
                                      "Computer Science",
                                      "Dan Smart"));
        sList.appendEntry(new GraduateStudent("Mel Lee", "333333333", 
                                      "0968333333", 
                                      "Mechanical Engineering",
                                      "Ron Rivest"));
        sList.appendEntry(new GraduateStudent("Bob Tsai", "444444444", 
                                      "0930444444", 
                                      "Electrical Engineering",
                                      "Alan Laub"));
        sList.appendEntry(new ForeignGraduateStudent("Ron Yang", "555555555", 
                                      "0918555555", 
                                      "Computer Science",
                                      "Allen Gersho",
                                      "Singapore"));
    
        int i;
        StudentListIterator iter1(sList), iter2(sList);
        for (i=0, iter1.reset(); 
             iter1.hasMoreData(); iter1.next(), i++)
        {
            cout << i << ":";
            iter1->display(cout);
            cout << endl;
        }
    
        sList.find("222222222")->display(cout); cout << " found!!" << endl;
    
        if (sList.deleteEntry("444444444"))
            cout << "Bob Tsai's entry deleted successfully!\n";
        else
            cout << "Bob Tsai's entry deletion failed!\n";
    
        if (sList.find("444444444") == 0)
            cout << "Can not find Bob Tsai's entry!\n";
    
    
        cout << endl;
        for (iter1.reset(); iter1.hasMoreData(); iter1.next())
        {
            for (iter2=iter1, iter2.next(); 
                 iter2.hasMoreData(); iter2.next())
            {
                if (iter1->ofTheSameDepartment(*iter2))
                {
                    cout << "The following two students"
                            " are of the same department:\n";
                    iter1->display(cout);
                    cout << endl;
                    iter2->display(cout);
                    cout << endl;
                }
            }
        }
    
        cout << endl;
        for (iter1.reset(); iter1.hasMoreData(); iter1.next())
            if (iter1->IDEquals("333333333"))
                sList.insertEntry(iter1, 
                    new UndergraduateStudent("Carol Chen", "333331111", 
                                          "0933333111", "Business",
                                          "John Fowler"));
        for (i=0; i<sList.size(); i++)
        {
            sList[i]->display(cout);
            cout << endl;
        }
    
        sList.dump();
    }

    void appendEntry(UndergraduateStudent *student);
    void insertEntry(StudentListIterator iter, UndergraduateStudent *student);
    void appendEntry(GraduateStudent *student);
    void insertEntry(StudentListIterator iter, GraduateStudent *student);
    void appendEntry(ForeignGraduateStudent *student);
    void insertEntry(StudentListIterator iter, ForeignGraduateStudent *student);

    class UndergraduateStudent: public Student
    {
    public:
        UndergraduateStudent(const char *name, const char *ID, 
                             const char *phone, const char *department,
                             const char *academicAdvisor);
        ~UndergraduateStudent();
        void display(ostream &os) const;
    private:
        char *m_academicAdvisor;
    };

建構元也需要在初始化串列中運用父類別的建構元函式初始化父類別物件

這個類別裡需要重新定義 void display(ostream &os) 函式, 除了基本資料之外, 額外列印 m_academicAdvisor

因為 UndergraduateStudent 類別的物件需要放進 StudentList 中, 同時 GraduateStudent 和 ForeignGraduateStudent 類別的物件也需要能夠放進 StudentList 中, 所以需要在 StudentList::Node 中改成運用 Student *m_data 這樣子的多型指標來記錄 (對於物件導向的設計來說, 所有衍生類別的物件都可以看成是一個父類別的物件來使用, 所以這個父類別的指標可以指到 UndergraduateStudent 類別的物件, 也可以指到 GraduateStudent 或是 ForeignGraduateStudent 類別的物件), 如果 Student 類別裡讓 display 界面定義為虛擬函式(在 void Student::display(ostream&) 函式前面加上 virtual 關鍵字), 運用 m_data->display(os) 來執行到的 display 函式是 m_data 指到的那個物件的類別所定義的 display 函式, 也就是說如果 m_data 指向一個 Undergraduate 類別的物件, m_data->display(os) 執行到的就是 Undergraduate::display(ostream& os) 函式。由於 StudentList 的解構元裡面用一個迴圈刪除所有由 m_data 指向的物件, 所以 Student 類別的解構元也需要定義為虛擬函式, virtual ~Student()。

做到這裡你可以先修改一下步驟二中的 main() 函式, 暫時先不使用 GraduateStudent 和 ForeignGraduateStudent 類別, 先用 StudentList 而不用 LoggedStudentList, 測試結果如下

0:[Mary Chen, 111111111, 0933111111, Business] [AcademicAdvisor:John Viega]
1:[John Wang, 222222222, 0928222222, Computer Science] [AcademicAdvisor:Dan Smart] 
2:[Mel Lee, 333333333, 0968333333, Mechanical Engineering] [AcademicAdvisor:Ron Rivest] 
3:[Bob Tsai, 444444444, 0930444444, Electrical Engineering] [AcademicAdvisor:Alan Laub] 
4:[Ron Yang, 555555555, 0918555555, Computer Science] [AcademicAdvisor:Allen Gersho] 
[John Wang, 222222222, 0928222222, Computer Science] [AcademicAdvisor:Dan Smart] found!!
Bob Tsai's entry deleted successfully!
Can not find Bob Tsai's entry!
...

使用步驟二中的 main() 函式, 先用 StudentList 取代 LoggedStudentList 測試一下, 結果如下:

0:[Mary Chen, 111111111, 0933111111, Business] [AcademicAdvisor:John Viega]
1:[John Wang, 222222222, 0928222222, Computer Science] [AcademicAdvisor:Dan Smart]
2:[Mel Lee, 333333333, 0968333333, Mechanical Engineering] [Advisor:Ron Rivest]
3:[Bob Tsai, 444444444, 0930444444, Electrical Engineering] [Advisor:Alan Laub]
4:[Ron Yang, 555555555, 0918555555, Computer Science] [Advisor:Allen Gersho] 
                                          [Nationality:Singapore]
[John Wang, 222222222, 0928222222, Computer Science] [AcademicAdvisor:Dan Smart] found!!    
Bob Tsai's entry deleted successfully!
Can not find Bob Tsai's entry!
...

使用步驟二中的 main() 函式測試一下, 螢幕顯示結果如下:

0:[Mary Chen, 111111111, 0933111111, Business] [AcademicAdvisor:John Viega]
1:[John Wang, 222222222, 0928222222, Computer Science] [AcademicAdvisor:Dan Smart]
2:[Mel Lee, 333333333, 0968333333, Mechanical Engineering] [Advisor:Ron Rivest]
3:[Bob Tsai, 444444444, 0930444444, Electrical Engineering] [Advisor:Alan Laub]
4:[Ron Yang, 555555555, 0918555555, Computer Science] [Advisor:Allen Gersho] 
                                          [Nationality:Singapore]
[John Wang, 222222222, 0928222222, Computer Science] [AcademicAdvisor:Dan Smart] found!!    
Bob Tsai's entry deleted successfully!
Can not find Bob Tsai's entry!
...

請檢查所產生的 main2.log 檔案內的記錄資料

LoggedStudentList::appendEntry()
   [Mary Chen, 111111111, 0933111111, Business] [AcademicAdvisor:John Viega]
LoggedStudentList::appendEntry()
   [John Wang, 222222222, 0928222222, Computer Science] [AcademicAdvisor:Dan Smart]
LoggedStudentList::appendEntry()
   [Mel Lee, 333333333, 0968333333, Mechanical Engineering] [Advisor:Ron Rivest]
LoggedStudentList::appendEntry()
   [Bob Tsai, 444444444, 0930444444, Electrical Engineering] [Advisor:Alan Laub]
...

    virtual void display(std::ostream &os) const=0;

在這個實習中所完成的異質容器物件架構，雖然不是這個 Strategy 樣板，但是 StudentList - Student/UndergraduateStudent/GraduateStudent 的架構及基本設計精神和這個 Strategy 設計樣板是一致的，最主要是運用 Strategy 這個抽象界面來分隔 (Decouple) Player 類別以及 WinningStrategy 或是 RandomStrategy 類別，在設計的過程中主要滿足了 Dependency-Inversion Principle，設計出來的結果也滿足了 Open-Closed Principle，其中 Student 抽象基礎類別以及運用這個類別的 main() 函式是 open for extension 但是 closed for modification 的，需要增加的功能完全寫在由 Student 類別衍生出來的子類別中。