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!
正确答案及解析
正确答案
解析
（1）ticket.printInvoice()
（2）super.printInvoice()
（3）super.printInvoice()
（4）new HeadDecorator(new FootDecorator(t))
（5）new HeadDecorator(new FootDecorator(null))
本题考查的是面向对象程序设计和设计模式。本题涉及的设计模式是装饰模式。
装饰模式（Decorator）：动态地给一个对象添加一些额外的职责。它提供了用子类扩展功能的一个灵活的替代，比派生一个子类更加灵活。
对于程序填空可以参照代码上下文、题干说明和设计模式综合考虑。
对于第（1）空，是对printInvoice方法的具体调用，在Decorator是装饰类，继承了Invoice发票类。此处需要填写的是printInvoice方法的方法体，根据Decorator类的上下文，已定义ticket对象，所以此处调用printInvoice方法的是ticket，第（1）空填写ticket.printInvoice()。
对于第（2）（3）空，根据类图可知，分别是HeadDecorator抬头类、FootDecorator脚注类调用printInvoice方法的方法体，由于在这两个类中并没有定义属性，只有借助其超类的构造函数，所以这两个地方调用printInvoice方法的是它们的超类，即（2）（3）填写的是super.printInvoice()。
对于第（4）（5）空，考查的是对装饰模式的调用，都是main函数中实例化的过程，根据输出结果可以看到，第（4）空实例化ticket对象，可以输出抬头、内容、脚注3个部分，因此需要调用三者的printInvoice()方法，前面已经实例化了一个Invoice对象t，可以利用t给子类实例化，因此第（4）空填写new HeadDecorator(new FootDecorator(t))；而第（5）空没有输出具体内容，只有抬头和脚注部分，可以看到这里的Invoice对象应该是空，所以第（5）空填写new HeadDecorator(new FootDecorator(null))。
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