Added more JavaDocs

java/com.sap.sse.security/src/com/sap/sse/security/PreferenceObjectListener.java

@@ -3,8 +3,23 @@ package com.sap.sse.security;
 /**
  * Listener used by UserStore to notify about changes of stored preference objects.
  *
- * @param <PrefT> The type of preference object this Listener handles.
+ * @param <PrefT>
+ *            The type of preference object this Listener handles.
  */
 public interface PreferenceObjectListener<PrefT> {
+    /**
+     * Called when the preference object for the given user and preference key has changed.
+     * 
+     * @param username
+     *            the user for whom the preference object changed
+     * @param key
+     *            the key of the changed preference object
+     * @param oldPreference
+     *            the old state of the preference object. May be <code>null</code> if there was not preference object
+     *            formerly.
+     * @param newPreference
+     *            the new state of the preference object. May be <code>null</code> if the preference object is being
+     *            deleted.
+     */
     void preferenceObjectChanged(String username, String key, PrefT oldPreference, PrefT newPreference);
 }