阅读下列说明和C++-代码，将应填入 （n） 处的字句写在答题纸的对应栏内。 【说明】 某发票（lnvoice）由抬头（Head）部分、正文部分和脚注（Foot）部分构成。现采用装饰（ Decorator）模式实现打印发票的功能，得到如图5-1所示的类图。 【C++代码】 #include ＜iostream> using namespace std; class Invoice{ public: （1） { cout＜＜"This is the content of the invoice!"＜＜endl; } }; class Decorator : public Invoice { Invoice *ticket; public: Decorator(lnvoice *t) { ticket = t; } void printInvoice（ ）{ if(ticket != NULL) （2）; } }; class HeadDecorator : public Decorator{ public: HeadDecorator(lnvoice*t): Decorator(t) { } void printInvoice（ ） { cout＜＜ "This is the header of the invoice! "＜＜ endl; （3） ; } }; class FootDecorator : public Decorator{ public: FootDecorator(Invoice *t): Decorator(t) { } void printlnvoice（ ）{ （4） ; cout＜＜ "This is the footnote of the invoice!"＜＜ endl; } }; int main(void) { Invoice t; FootDecorator f(&t); HeadDecorator h(&f); h.printInvoice（ ）; cout＜＜”------------------------”＜＜endl; FootDecorator a(NULL) ; HeadDecorator b( （5） ); b.printInvoice（ ）; return 0; } 程序的输出结果为： This is the header of the invoice! This is the content of the invoice! This is the footnote of the invoice! ---------------------------- This is the header of the invoice! This is the footnote of the invoice!

阅读下列说明和C++-代码，将应填入  （n）  处的字句写在答题纸的对应栏内。
【说明】 
   某发票（lnvoice）由抬头（Head）部分、正文部分和脚注（Foot）部分构成。现采用装饰（ Decorator）模式实现打印发票的功能，得到如图5-1所示的类图。

【C++代码】
#include
＜iostream>
using
namespace std;
class Invoice{
public:
    （1）   {       
   cout＜＜"This is the content of the
invoice!"＜＜endl;
    }
};
class
Decorator : public Invoice {
     Invoice *ticket;
public:
    Decorator(lnvoice *t)      { ticket = t; }
     void printInvoice（ ）{
         if(ticket != NULL)
 （2）;
   }
 };
class
HeadDecorator : public Decorator{
public:
    HeadDecorator(lnvoice*t): Decorator(t) { }
     void printInvoice（ ） {
            cout＜＜ "This is the
header of the invoice! "＜＜ endl;
     （3）     ;
    }
  };
   class FootDecorator : public Decorator{
 public:
    FootDecorator(Invoice *t): Decorator(t) { }
     void printlnvoice（ ）{
                 （4）   ;
             cout＜＜ "This is the
footnote of the invoice!"＜＜ endl;
    }
};
int main(void)
{
    Invoice t;
    FootDecorator f(&t);
    HeadDecorator h(&f);
    h.printInvoice（ ）;
   
cout＜＜”------------------------”＜＜endl;
    FootDecorator a(NULL) ;                                                                                                             
                      
    HeadDecorator b(     （5）   );
    b.printInvoice（ ）;
    return 0;
}
程序的输出结果为：
    This is the header of the invoice!
    This is the content of the invoice!
    This is the footnote of the invoice!
    ----------------------------
    This is the header of the invoice!
    This is the footnote of the invoice!