diff -r 09d690bb97f6 -r 58ec6da75f6f task4/solution11/src/org/apidesign/apifest08/currency/ExchangeRateProvider.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/task4/solution11/src/org/apidesign/apifest08/currency/ExchangeRateProvider.java	Sat Oct 11 23:38:46 2008 +0200
@@ -0,0 +1,55 @@
+package org.apidesign.apifest08.currency;
+
+/**
+ * Exchange rate provider.
+ * 
+ * @author ked
+ * @see http://wiki.apidesign.org/wiki/APIDesignPatterns:ResponseReply
+ */
+public interface ExchangeRateProvider<AmountType, IdentifierType> {
+
+    public void getExchangeRate(
+            ExchangeRateRequest<AmountType, IdentifierType> request,
+            ExchangeRateResponse<AmountType, IdentifierType> response);
+
+    public final class ExchangeRateRequest<AmountType, IdentifierType> {
+
+        private IdentifierType currencyAIdentifier;
+        private IdentifierType currencyBIdentifier;
+
+        ExchangeRateRequest() {
+        }
+
+        public IdentifierType getCurrencyAIdentifier() {
+            return currencyAIdentifier;
+        }
+
+        void setCurrencyAIdentifier(IdentifierType currencyAIdentifier) {
+            this.currencyAIdentifier = currencyAIdentifier;
+        }
+
+        public IdentifierType getCurrencyBIdentifier() {
+            return currencyBIdentifier;
+        }
+
+        void setCurrencyBIdentifier(IdentifierType currencyBIdentifier) {
+            this.currencyBIdentifier = currencyBIdentifier;
+        }
+    }
+
+    public final class ExchangeRateResponse<AmountType, IdentifierType> {
+
+        private ExchangeRateValue<AmountType, IdentifierType> exchangeRate;
+
+        ExchangeRateResponse() {
+        }
+
+        ExchangeRateValue<AmountType, IdentifierType> getExchangeRate() {
+            return exchangeRate;
+        }
+
+        public void setExchangeRate(ExchangeRateValue<AmountType, IdentifierType> exchangeRate) {
+            this.exchangeRate = exchangeRate;
+        }
+    }
+}