code: public Enumeration<String> getKeys() {
          // lazily load the lookup hashtable.
          if (lookup == null) {
              loadLookup();
          }
  
          ResourceBundle parent = this.parent;
          return new ResourceBundleEnumeration(lookup.keySet(),
                  (parent != null) ? parent.getKeys() : null);
      }
docs: Returns an <code>Enumeration</code> of the keys contained in
  this <code>ResourceBundle</code> and its parent bundles.
  
  @return an <code>Enumeration</code> of the keys contained in
  this <code>ResourceBundle</code> and its parent bundles.
  @see #keySet()