//Method that set next handler in the pipeline
public CurrencyBill RegisterNext(CurrencyBill currencyBill)
{
next = currencyBill;
return(next);
}
//A static constructor that initializes static Zero property
//This property is used as default next handler instead of a null object
static CurrencyBill()//静态构造函数的用法
{
Zero = new ZeroCurrencyBill();
}
