diff -r 14e78f48ac2b -r 58ec6da75f6f task4/solution04/src/org/apidesign/apifest08/currency/ConvertorFactory.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/task4/solution04/src/org/apidesign/apifest08/currency/ConvertorFactory.java	Sat Oct 11 23:38:46 2008 +0200
@@ -0,0 +1,177 @@
+package org.apidesign.apifest08.currency;
+
+import java.math.BigDecimal;
+import java.util.Currency;
+
+
+/**
+ * Create convertors using a flyweight to reduce the number of repetative creations of the same convertor.
+ * 
+ * @author D'Arcy Smith
+ * @version 1.0
+ */
+public final class ConvertorFactory
+{
+    /*
+     * flyweight so that only one vestion of each converter is created at a time.
+    private final static Map<String, WeakReference<Convertor>> convertors;
+    
+    static
+    {
+        convertors = new WeakHashMap<String, WeakReference<Convertor>>();
+    }
+    */
+    
+    /** 
+     * Prevent accidental construction.
+     */
+    private ConvertorFactory()
+    {        
+    }
+    
+    /**
+     * Get the convertor for the specified currencies.  The currency name format
+     * must be acceptable to java.util.Currency.getInstance(String)
+     * 
+     * @param a the currency to convert from.
+     * @param aRate the exchange rate for a to b.
+     * @param b the currency to convert to.
+     * @param bRate the echante rate for b to a.
+     * @return the convertor for the specified currencies.
+     * @throws IllegalArgumentException if any of the arguments are null.
+     */
+    public static Convertor getConvertor(final String     a,
+                                         final BigDecimal aRate,
+                                         final String     b,
+                                         final BigDecimal bRate)
+    {
+        final Currency  currencyA;
+        final Currency  currencyB;
+        final Convertor convertor;
+        
+        currencyA = Currency.getInstance(a);
+        currencyB = Currency.getInstance(b);        
+        convertor = getConvertor(currencyA, aRate, currencyB, bRate);
+        
+        return (convertor);
+    }
+    
+    /**
+     * Get the convertor for the specified currencies.
+     * 
+     * @param a the currency to convert from.
+     * @param aRate the exchange rate for a to b.
+     * @param b the currency to convert to.
+     * @param bRate the echante rate for b to a.
+     * @return the convertor for the specified currencies.
+     * @throws IllegalArgumentException if either any of the arguments are null or if either rate <= 0.
+     */
+    public static Convertor getConvertor(final Currency   a,
+                                         final BigDecimal aRate,
+                                         final Currency   b,
+                                         final BigDecimal bRate)
+    {
+        // final String key;        
+        Convertor    convertor;
+
+        if(a == null)
+        {
+            throw new IllegalArgumentException("a cannot be null");
+        }
+
+        if(b == null)
+        {
+            throw new IllegalArgumentException("b cannot be null");
+        }
+        
+        if(aRate == null)
+        {
+            throw new IllegalArgumentException("aRate cannot be null");
+        }
+        
+        if(bRate == null)
+        {
+            throw new IllegalArgumentException("bRate cannot be null");
+        }
+
+        /*
+        key = a.getCurrencyCode() + aRate + b.getCurrencyCode() + bRate;
+
+        // make sure that we don't try to overwrite one
+        synchronized(convertors)
+        {
+            if(!(convertors.containsKey(key)))
+            {        
+                convertor = new ConvertorImpl(a, aRate, b, bRate);
+                convertors.put(key, new WeakReference(convertor));
+            }
+
+            convertor = convertors.get(key).get();
+        }
+        */
+        
+        convertor = new ConvertorImpl(a, aRate, b, bRate);
+                
+        return (convertor);
+    }
+    
+    /**
+     * 
+     * @param cs
+     * @return
+     */
+    public static Convertor mergeConvertors(final Convertor ... cs)
+    {
+        Convertor convertor;
+        
+        /*
+        final String key;
+
+        // ISSUE: only takes into account the names... not the rates...
+        key = getKey(cs);
+
+        // make sure that we don't try to overwrite one
+        synchronized(convertors)
+        {
+            if(!(convertors.containsKey(key)))
+            {        
+                convertor = new CompositeConvertorImpl(cs);
+                convertors.put(key, new WeakReference(convertor));
+            }
+
+            convertor = convertors.get(key).get();
+        }
+        */
+        
+        convertor = new CompositeConvertorImpl(cs);
+        
+        return (convertor);
+    }
+
+    /*
+    private static String getKey(final Convertor ... cs)
+    {
+        final Set<Currency> currencies;
+        final StringBuilder builder;
+        
+        currencies = new HashSet<Currency>();
+        
+        for(final Convertor convertor : cs)
+        {
+            final Set<Currency> c;
+            
+            c = convertor.getCurrencies();
+            currencies.addAll(c);
+        }
+        
+        builder = new StringBuilder();
+
+        for(final Currency currency : currencies)
+        {
+            builder.append(currency.getCurrencyCode());
+        }
+        
+        return (builder.toString());
+    }
+    */
+}