diff -r f6073056b9fe -r a7e6f84fb078 task2/solution13/src/org/apidesign/apifest08/currency/ExchangeRate.java
--- a/task2/solution13/src/org/apidesign/apifest08/currency/ExchangeRate.java	Wed Oct 01 10:43:05 2008 +0200
+++ b/task2/solution13/src/org/apidesign/apifest08/currency/ExchangeRate.java	Tue Oct 07 01:18:23 2008 +0200
@@ -12,20 +12,47 @@
     private BigDecimal numberFor;
     private BigDecimal numberGet;
 
+    /**
+     * Constructor for new exchange rate holding two values - <em>from value</em> and <em>to value</em>
+     * @param fromValue Exchange rate <em>from value</em>
+     * @param toValue Exchange rate <em>to value</em>
+     */
     public  ExchangeRate(BigDecimal fromValue, BigDecimal toValue) {
         this.numberFor = fromValue;
         this.numberGet = toValue;
     }
+    
+    /**
+     * Create new instance of <code>ExchangeRate</code> based on provided exchange rate, but swapping its
+     * <em>from</em> and <em>to</em> value.
+     * <p>
+     * Provided exchange rate is not chaged, this method returns different instance describing reverted exchange rate.
+     * 
+     * @param rate Exchange rate which describes rate to be reverted.
+     * @return Instance of reverted rate.
+     */
+    public static ExchangeRate createRevertedRate(ExchangeRate rate) {
+        ExchangeRate reverted = new ExchangeRate(rate.getToValue(), rate.getFromValue());
+        return reverted;
+    }
 
     @Override
     public String toString() {
         return "for "+numberFor+" recieve "+numberGet+" @"+getClass().getName();
     }
     
+    /**
+     * Return exchange rate <em>from</em> value stored in this object.
+     * @return Returns <em>from</em> value for this exchange rate.
+     */
     public BigDecimal getFromValue() {
         return numberFor;
     }
     
+    /**
+     * Return exchange rate <em>to</em> value stored in this object.
+     * @return Returns <em>to</em> value for this exchange rate.
+     */
     public BigDecimal getToValue() {
         return numberGet;
     }