diff -r 14e78f48ac2b -r 58ec6da75f6f task4/solution04/src/org/apidesign/apifest08/currency/OnlineConvertor.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/task4/solution04/src/org/apidesign/apifest08/currency/OnlineConvertor.java	Sat Oct 11 23:38:46 2008 +0200
@@ -0,0 +1,175 @@
+package org.apidesign.apifest08.currency;
+
+
+import java.math.BigDecimal;
+import java.util.Currency;
+import java.util.Set;
+
+
+/**
+ * A Convertor that looks up the exchange rate with each call to "convert".
+ *
+ * @author D'Arcy Smith
+ * @version 1.0
+ */
+public class OnlineConvertor
+    implements Convertor
+{
+    /**
+     * The currency to convert from.
+     */
+    private final Currency currencyA;
+
+    /**
+     * The currency to convert to.
+     */
+    private final Currency currencyB;
+
+    /**
+     * Used to find the current exchange rate.
+     */
+    private final ExchangeRateFinder finder;
+    
+    /**
+     * The convertor to perform the conversion.
+     */
+    private Convertor realConvertor;
+
+    /**
+     * Constructs an OnlinConvertor with the specified currencies.
+     * 
+     * @param a the currency to convert from.
+     * @param b the currency to convert to.
+     * @param f the finder used to obtanin the current exchange rate.
+     * @throws IllegalArgumentException if either a or b are null.
+     */
+    public OnlineConvertor(final Currency           a,
+                           final Currency           b,
+                           final ExchangeRateFinder f)
+    {
+        if(a == null)        
+        {
+            throw new IllegalArgumentException("a cannot be null");
+        }
+        
+        if(b == null)
+        {
+            throw new IllegalArgumentException("b cannot be null");
+        }
+        
+        if(f == null)
+        {
+            throw new IllegalArgumentException("f cannot be null");
+        }
+        
+        currencyA     = a;
+        currencyB     = b;
+        finder        = f;
+        realConvertor = lookupRate();
+    }
+
+    /**
+     * Convert an amount from one currency to another.  Before the conversion takes place 
+     * the current exchange rate is looked up.
+     *
+     * @param from the currency to convert from.
+     * @param to the currency to convert to.
+     * @param amount the amount to convert.
+     * @return the converted amount.
+     * @throws IllegalArgumentException if any of the arguments are null.
+     * @throws InvalidConversionException if either from or to are not equal to the currencies passed to the constructor.
+     */
+    public BigDecimal convert(final Currency   from, 
+                              final Currency   to, 
+                              final BigDecimal amount) 
+        throws InvalidConversionException
+    {
+        final BigDecimal value;
+        
+        synchronized(this)
+        {
+            realConvertor = lookupRate();
+            value         = realConvertor.convert(from, to, amount);
+        }
+        
+        return (value);
+    }
+
+    /**
+     * Lookup the current exchange rate.
+     * 
+     * @return
+     */
+    private final Convertor lookupRate()
+    {
+        final Convertor convertor;
+        final ExchangeRate rate;
+
+        rate      = finder.findRate(currencyA, currencyB);
+        convertor = ConvertorFactory.getConvertor(rate.getCurrencyA(), rate.getRateAtoB(), rate.getCurrencyB(), rate.getRateBtoA());
+
+        return (convertor);
+    }
+
+    /**
+     * Check to see if converting between the two currencies is possible.
+     * 
+     * @param from the currency to convert from.
+     * @param to the currency to convert to.
+     * @return true if the conversion is possible.
+     * @throws IllegalArgumentException if either from or to are null.
+     */
+    public boolean canConvert(final Currency from, 
+                              final Currency to) 
+    {
+        if(from == null)
+        {
+            throw new IllegalArgumentException("from cannot be null");
+        }
+        
+        if(to == null)
+        {
+            throw new IllegalArgumentException("to cannot be null");
+        }
+        
+        return (realConvertor.canConvert(from, to));
+    }
+
+    /**
+     * Get the currencies that the convertor supports.
+     * 
+     * @return the supported currencies.
+     */
+    public Set<Currency> getCurrencies() 
+    {
+        return (realConvertor.getCurrencies());
+    }
+
+    /**
+     * Get the conversion rate between two currencies.  This does not lookup the current
+     * conversion rate (it probably should, but given the way the contest works that might 
+     * not be a good idea - if it were the real world way it might be a good idea).
+     * 
+     * @param from the currency to convert from.
+     * @param to the currency to convert to.
+     * @return the conversion rate between the two currencies.
+     * @throws InvalidConversionException if canConvert would return false.
+     * @throws IllegalArgumentException if either from or to are null.
+     */
+    public BigDecimal getConversionRate(final Currency from, 
+                                        final Currency to) 
+        throws InvalidConversionException 
+    {        
+        if(from == null)
+        {
+            throw new IllegalArgumentException("from cannot be null");
+        }
+        
+        if(to == null)
+        {
+            throw new IllegalArgumentException("to cannot be null");
+        }
+        
+        return (realConvertor.getConversionRate(from, to));
+    }    
+}