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);

}

}