阅读下列说明和java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6-1所示的类图。 【java代码】 class invoice{ public void printInvoice（ ）{ System.out.println ( "This is the content of the invoice!"); } } class Decorator extends Invoice { protected Invoice ticket; public Decorator(lnvoice t){ ticket = t; } public void printInvoice（ ）{ if(ticket != null) （1） ; } } class HeadDecorator extends Decorator{ public HeadDecorator(lnvoice t){ super(t); } public void printInvoice （ ）{ Systent.out.println( "This is the header of the invoice! "); （2） ; } } class FootDecorator extends Decorator { public FootDecorator(Invoice t){ super(t); } public void printlnvoice（ ）{ （ 3） ; Systent.out.println( "This is the footnote of the invoice! "); } } Class test { public static void main(String[] args){ Invoice t =new Invioce（ ）; Invoice ticket; ticket= （4） ; ticket.printInvoice（ ）; Systent.out.println(“------------------“); ticket= （5） ; ticket.printInvoice（ ）; } } 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java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6-1所示的类图。

【java代码】
class invoice{
public void printInvoice（ ）{ 
          
System.out.println ( "This is the content of the invoice!");
    }
}
class Decorator extends Invoice {
  
protected Invoice ticket;
  
public Decorator(lnvoice t){
        
ticket = t;
}
   public
void printInvoice（ ）{
        
if(ticket != null)
                          （1）       ;
 
}  
}
class HeadDecorator extends Decorator{
      
public HeadDecorator(lnvoice t){
          
super(t);
}
    
public void printInvoice （ ）{
           
Systent.out.println( "This is the header of the invoice! ");
                          （2）         ;
    }
}
 class FootDecorator extends Decorator {
   
public FootDecorator(Invoice t){
   
super(t);
}
    
public void printlnvoice（ ）{
      
                （ 3）        ;
            
Systent.out.println( "This is the footnote of the invoice! ");
    }
}
Class test {
   
public static void main(String[] args){
    
Invoice t =new Invioce（ ）;
    
Invoice ticket;
    
ticket=     （4）       ;
    
ticket.printInvoice（ ）;
    
Systent.out.println(“------------------“);
    
ticket=       （5）       ;
    
ticket.printInvoice（ ）;
   }
}
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!