Review

class AttributeSource {
  /** Returns a new iterator that iterates the attribute classes
   * in the same order they were added in.
   * <p>Signature for Java 1.5: <code>public Iterator&lt;Class&lt;? extends Attribute&gt;&gt; getAttributeClassesIterator()</code>
   */
  public Iterator getAttributeClassesIterator() {
    return Collections.unmodifiableSet(attributes.keySet()).iterator();
  }

}