这里我们定义一个java接口，表示了“金钱”这个神奇东西的一些美妙的抽象方法！早年有首迟志强的歌叫《钞票》：是谁制造的钞票，你在世上逞霸道，有人为你愁眉苦脸啊有人为你哈哈笑；姑娘为你走错了路，小伙子为你受改造！东奔又西跑，点头又哈腰，钞票！人人为你离不了钱哪！你这杀人不见血的刀…形象无比，不扯了，跑题啦！I am back!
之后我们实现这个接口，在src文件夹下定义一个叫做Money.java的类：
public class Money implements IMoney {
private int fAmount;
private String fCurrency;
/**
* Constructs a money from the given amount and currency.
*/
public Money(int amount， String currency) {
fAmount= amount;
fCurrency= currency;
}
/**
* Adds a money to this money. Forwards the request to the addMoney helper.
*/
public IMoney add(IMoney m) {
return m.addMoney(this);
}
public IMoney addMoney(Money m) {
if (m.currency().equals(currency()) )
return new Money(amount()+m.amount()， currency());
return MoneyBag.create(this， m);
}
public IMoney addMoneyBag(MoneyBag s) {
return s.addMoney(this);
}
public int amount() {
return fAmount;
}
public String currency() {
return fCurrency;
}
public boolean equals(Object anObject) {
if (isZero())
if (anObject instanceof IMoney)
return ((IMoney)anObject).isZero();
if (anObject instanceof Money) {
Money aMoney= (Money)anObject;
return aMoney.currency().equals(currency())
&& amount() == aMoney.amount();
}
return false;
}
public int hashCode() {
return fCurrency.hashCode()+fAmount;
}
public boolean isZero() {
return amount() == 0;
}
public IMoney multiply(int factor) {
return new Money(amount()*factor， currency());
}
public IMoney negate() {
return new Money(-amount()， currency());
}
public IMoney subtract(IMoney m) {
return add(m.negate());
}
public String toString() {
StringBuffer buffer = new StringBuffer();
buffer.append("["+amount()+" "+currency()+"]");
return buffer.toString();
}
public /*this makes no sense*/ void appendTo(MoneyBag m) {
m.appendMoney(this);
}
}
