8.5 Design the data structures for an online book reader system.
这道题OOB的题让我们设计一个在线读书系统，还是没有任何提示，所以发挥空间很大。根据书上的解答，我们设计一个具有基本功能的系统：
1. 用户会员的建立和延长
2. 搜索书库中的书
3. 在线读书
4. 每次只能有一个活跃用户
5. 每个读者只能读一本书
那么最基本的先实现书类Book，和用户类User，然后是书库类Library，用户管理类UserManager，显示类Display，最后是整合类OnlineReaderSystem，具体实现代码如下：
class Book {
public:
Book(int id, string det): _bookId(id), _details(det) {}
int getID() { return _bookId; }
void setId(int id) { _bookId = id; }
string getDetails() { return _details; }
void setDetails(string d) { _details = d; }
private:
int _bookId;
string _details;
};
class User {
public:
User(int id, string details, int accountType): _userId(id), _details(details), _accountType(accountType) {}
void renewMembership() {}
int getID() { return _userId; }
void setID(int id) { _userId = id; }
string getDetails() { return _details; }
void setDetails(string details) { _details = details; }
int getAccountType() { return _accountType; }
void setAccountType(int t) { _accountType = t; }
private:
int _userId;
string _details;
int _accountType;
};
class Library {
public:
Library() {}
Book* addBook(int id, string details) {
if (_books.find(id) == _books.end()) return nullptr;
Book *book = new Book(id, details);
_books[id] = book;
return book;
}
bool remove(Book *b) { return remove(b->getID()); }
bool remove(int id) {
if (_books.find(id) == _books.end()) return false;
_books.erase(id);
return true;
}
Book* find(int id) {
if (_books.find(id) == _books.end()) return nullptr;
return _books[id];
}
private:
unordered_map<int, Book*> _books;
};
class UserManager {
public:
UserManager() {}
User* addUser(int id, string details, int accountType) {
if (_users.find(id) == _users.end()) return nullptr;
User *user = new User(id, details, accountType);
_users[id] = user;
return user;
}
bool remove(User *u) { return remove(u->getID()); }
bool remove(int id) {
if (_users.find(id) == _users.end()) return false;
_users.erase(id);
return true;
}
User* find(int id) {
if (_users.find(id) == _users.end()) return nullptr;
return _users[id];
}
private:
unordered_map<int, User*> _users;
};
class Display {
public:
Display() {}
void displayUser(User *user) {
_activeUser = user;
refreshUsername();
}
void displayBook(Book *book) {
_pageNumber = ;
_activeBook = book;
refreshTitle();
refreshDetails();
refreshPage();
}
void turnPageForward() {
++_pageNumber;
refreshPage();
}
void turnPageBackward() {
--_pageNumber;
refreshPage();
}
void refreshUsername() {} // ...
void refreshTitle() {} // ...
void refreshDetails() {} // ...
void refreshPage() {} // ...
private:
Book *_activeBook;
User *_activeUser;
int _pageNumber = ;
};
class OnlineReaderSystem {
public:
OnlineReader() {
_userManager = new UserManager();
_library = new Library();
_display = new Display();
}
Library* getLibrary() { return _library; }
UserManager* getUserManager() { return _userManager; }
Display* getDisplay() { return _display; }
Book* getActiveBook() { return _activeBook; }
void setActiveBook(Book *book) {
_activeBook = book;
_display->displayBook(book);
}
User* getActiveUser() { return _activeUser; }
void setActiveUser(User *user) {
_activeUser = user;
_display->displayUser(user);
}
private:
Library *_library;
UserManager *_userManager;
Display *_display;
Book *_activeBook;
User *_activeUser;
};