MoneyBag.java

package junit.samples.money;

import java.util.ArrayList;
import java.util.List;

/**
 * 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. 
 */ 
public class MoneyBag implements IMoney {
	private List<Money> fMonies= new ArrayList<Money>(5);

	public 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 (Money each : aBag.fMonies)
			appendMoney(each);
	}
	void appendMoney(Money aMoney) {
		if (aMoney.isZero()) return;
		IMoney old= findMoney(aMoney.currency());
		if (old == null) {
			fMonies.add(aMoney);
			return;
		}
		fMonies.remove(old);
		Money sum= (Money) old.add(aMoney);
		if (sum.isZero()) 
			return;
		fMonies.add(sum);
	}
	@Override
	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 (Money each : fMonies)
		        if (! aMoneyBag.contains(each))
					return false;
			return true;
		}
		return false;
	}
	private Money findMoney(String currency) {
		for (Money each : fMonies)
			if (each.currency().equals(currency))
				return each;
		return null;
	}
	private boolean contains(Money m) {
		Money found= findMoney(m.currency());
		if (found == null) return false;
		return found.amount() == m.amount();
	}
	@Override
	public int hashCode() {
		int hash= 0;
	    for (Money each : fMonies)
	        hash^= each.hashCode();
	    return hash;
	}
	public boolean isZero() {
		return fMonies.size() == 0;
	}
	public IMoney multiply(int factor) {
		MoneyBag result= new MoneyBag();
		if (factor != 0)
			for (Money each : fMonies)
				result.appendMoney((Money) each.multiply(factor));
		return result;
	}
	public IMoney negate() {
		MoneyBag result= new MoneyBag();
	    for (Money each : fMonies)
	        result.appendMoney((Money) each.negate());
		return result;
	}
	private IMoney simplify() {
		if (fMonies.size() == 1)
			return fMonies.iterator().next();
		return this;
	}
	public IMoney subtract(IMoney m) {
		return add(m.negate());
	}
	@Override
	public String toString() {
		StringBuffer buffer = new StringBuffer();
		buffer.append("{");
		for (Money each : fMonies)
		    buffer.append(each);
		buffer.append("}");
		return buffer.toString();
	}
	public void appendTo(MoneyBag m) {
		m.appendBag(this);
	}
}