moneybag.java~3~

来自「数据库应用程序.它比较全面的含盖了JAVA应用程序与数据库之间通讯的全过程.本程」· JAVA~3~ 代码 · 共 199 行

package chapter25.money;

import java.util.*;

/**
 * A MoneyBag defers exchange rate conversions. For example adding
 * 12 Swiss Francs to 14 US Dollars is represented as a bag
 * containing the two Monies 12 CHF and 14 USD. Adding another
 * 10 Swiss francs gives a bag with 22 CHF and 14 USD. Due to
 * the deferred exchange rate conversion we can later value a
 * MoneyBag with different exchange rates.
 *
 * A MoneyBag is represented as a list of Monies and provides
 * different constructors to create a MoneyBag.
 */
class MoneyBag
    implements IMoney
{
    private Vector fMonies = new Vector(5);

    static IMoney create(IMoney m1, IMoney m2)
    {
        MoneyBag result = new MoneyBag();
        m1.appendTo(result);
        m2.appendTo(result);
        return result.simplify();
    }

    public IMoney add(IMoney m)
    {
        return m.addMoneyBag(this);
    }

    public IMoney addMoney(Money m)
    {
        return MoneyBag.create(m, this);
    }

    public IMoney addMoneyBag(MoneyBag s)
    {
        return MoneyBag.create(s, this);
    }

    void appendBag(MoneyBag aBag)
    {
        for (Enumeration e = aBag.fMonies.elements(); e.hasMoreElements(); )
        {
            appendMoney( (Money) e.nextElement());
        }
    }

    void appendMoney(Money aMoney)
    {
        if (aMoney.isZero())
        {
            return;
        }
        IMoney old = findMoney(aMoney.currency());
        if (old == null)
        {
            fMonies.addElement(aMoney);
            return;
        }
        fMonies.removeElement(old);
        IMoney sum = old.add(aMoney);
        if (sum.isZero())
        {
            return;
        }
        fMonies.addElement(sum);
    }

    public boolean equals(Object anObject)
    {
        if (isZero())
        {
            if (anObject instanceof IMoney)
            {
                return ( (IMoney) anObject).isZero();
            }
        }

        if (anObject instanceof MoneyBag)
        {
            MoneyBag aMoneyBag = (MoneyBag) anObject;
            if (aMoneyBag.fMonies.size() != fMonies.size())
            {
                return false;
            }

            for (Enumeration e = fMonies.elements(); e.hasMoreElements(); )
            {
                Money m = (Money) e.nextElement();
                if (!aMoneyBag.contains(m))
                {
                    return false;
                }
            }
            return true;
        }
        return false;
    }

    private Money findMoney(String currency)
    {
        for (Enumeration e = fMonies.elements(); e.hasMoreElements(); )
        {
            Money m = (Money) e.nextElement();
            if (m.currency().equals(currency))
            {
                return m;
            }
        }
        return null;
    }

    private boolean contains(Money m)
    {
        Money found = findMoney(m.currency());
        if (found == null)
        {
            return false;
        }
        return found.amount() == m.amount();
    }

    public int hashCode()
    {
        int hash = 0;
        for (Enumeration e = fMonies.elements(); e.hasMoreElements(); )
        {
            Object m = e.nextElement();
            hash ^= m.hashCode();
        }
        return hash;
    }

    public boolean isZero()
    {
        return fMonies.size() == 0;
    }

    public IMoney multiply(int factor)
    {
        MoneyBag result = new MoneyBag();
        if (factor != 0)
        {
            for (Enumeration e = fMonies.elements(); e.hasMoreElements(); )
            {
                Money m = (Money) e.nextElement();
                result.appendMoney( (Money) m.multiply(factor));
            }
        }
        return result;
    }

    public IMoney negate()
    {
        MoneyBag result = new MoneyBag();
        for (Enumeration e = fMonies.elements(); e.hasMoreElements(); )
        {
            Money m = (Money) e.nextElement();
            result.appendMoney( (Money) m.negate());
        }
        return result;
    }

    private IMoney simplify()
    {
        if (fMonies.size() == 1)
        {
            return (IMoney) fMonies.elements().nextElement();
        }
        return this;
    }

    public IMoney subtract(IMoney m)
    {
        return add(m.negate());
    }

    public String toString()
    {
        StringBuffer buffer = new StringBuffer();
        buffer.append("{");
        for (Enumeration e = fMonies.elements(); e.hasMoreElements(); )
        {
            buffer.append(e.nextElement());
        }
        buffer.append("}");
        return buffer.toString();
    }

    public void appendTo(MoneyBag m)
    {
        m.appendBag(this);
    }
}