5.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!
