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package org.apidesign.apifest08.currency;
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import java.math.BigDecimal;
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import java.util.Currency;
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import java.util.Set;
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/**
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* A Convertor that looks up the exchange rate with each call to "convert".
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*
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* @author D'Arcy Smith
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* @version 1.0
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*/
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public class OnlineConvertor
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implements Convertor
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{
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/**
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* The currency to convert from.
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*/
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private final Currency currencyA;
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/**
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* The currency to convert to.
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*/
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private final Currency currencyB;
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/**
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* Used to find the current exchange rate.
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*/
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private final ExchangeRateFinder finder;
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/**
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* The convertor to perform the conversion.
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*/
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private Convertor realConvertor;
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/**
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* Constructs an OnlinConvertor with the specified currencies.
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*
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* @param a the currency to convert from.
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* @param b the currency to convert to.
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* @param f the finder used to obtanin the current exchange rate.
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* @throws IllegalArgumentException if either a or b are null.
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*/
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public OnlineConvertor(final Currency a,
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final Currency b,
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final ExchangeRateFinder f)
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{
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if(a == null)
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{
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throw new IllegalArgumentException("a cannot be null");
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}
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if(b == null)
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{
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throw new IllegalArgumentException("b cannot be null");
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}
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if(f == null)
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{
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throw new IllegalArgumentException("f cannot be null");
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}
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currencyA = a;
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currencyB = b;
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finder = f;
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realConvertor = lookupRate();
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}
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/**
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* Convert an amount from one currency to another. Before the conversion takes place
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* the current exchange rate is looked up.
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*
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* @param from the currency to convert from.
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* @param to the currency to convert to.
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* @param amount the amount to convert.
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* @return the converted amount.
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* @throws IllegalArgumentException if any of the arguments are null.
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* @throws InvalidConversionException if either from or to are not equal to the currencies passed to the constructor.
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*/
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public BigDecimal convert(final Currency from,
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final Currency to,
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final BigDecimal amount)
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throws InvalidConversionException
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{
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final BigDecimal value;
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synchronized(this)
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{
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realConvertor = lookupRate();
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value = realConvertor.convert(from, to, amount);
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}
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return (value);
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}
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/**
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* Lookup the current exchange rate.
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*
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* @return
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*/
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private final Convertor lookupRate()
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{
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final Convertor convertor;
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final ExchangeRate rate;
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rate = finder.findRate(currencyA, currencyB);
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convertor = ConvertorFactory.getConvertor(rate.getCurrencyA(), rate.getRateAtoB(), rate.getCurrencyB(), rate.getRateBtoA());
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return (convertor);
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}
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/**
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* Check to see if converting between the two currencies is possible.
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*
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* @param from the currency to convert from.
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* @param to the currency to convert to.
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* @return true if the conversion is possible.
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* @throws IllegalArgumentException if either from or to are null.
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*/
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public boolean canConvert(final Currency from,
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final Currency to)
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{
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if(from == null)
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{
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throw new IllegalArgumentException("from cannot be null");
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}
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if(to == null)
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{
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throw new IllegalArgumentException("to cannot be null");
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}
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return (realConvertor.canConvert(from, to));
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}
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/**
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* Get the currencies that the convertor supports.
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*
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* @return the supported currencies.
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*/
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public Set<Currency> getCurrencies()
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{
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return (realConvertor.getCurrencies());
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}
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/**
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* Get the conversion rate between two currencies. This does not lookup the current
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* conversion rate (it probably should, but given the way the contest works that might
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* not be a good idea - if it were the real world way it might be a good idea).
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*
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* @param from the currency to convert from.
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* @param to the currency to convert to.
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* @return the conversion rate between the two currencies.
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* @throws InvalidConversionException if canConvert would return false.
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* @throws IllegalArgumentException if either from or to are null.
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*/
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public BigDecimal getConversionRate(final Currency from,
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final Currency to)
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throws InvalidConversionException
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{
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if(from == null)
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{
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throw new IllegalArgumentException("from cannot be null");
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}
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if(to == null)
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{
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throw new IllegalArgumentException("to cannot be null");
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}
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return (realConvertor.getConversionRate(from, to));
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}
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}
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