code: public static <K, V> ConvertingComparator<Map.Entry<K, V>, K> mapEntryKeys(
  			Comparator<K> comparator) {
  		return new ConvertingComparator<Map.Entry<K,V>, K>(comparator, new Converter<Map.Entry<K, V>, K>() {
  
  			public K convert(Map.Entry<K, V> source) {
  				return source.getKey();
  			}
  		});
  	}
docs: Create a new {@link ConvertingComparator} that compares {@link java.util.Map.Entry
  map * entries} based on their {@link java.util.Map.Entry#getKey() keys}.
  
  @param comparator the underlying comparator used to compare keys
  @return a new {@link ConvertingComparator} instance