code: public static <T> List<T> swap(List<T> self, int i, int j) {
          Collections.swap(self, i, j);
          return self;
      }
docs: Swaps two elements at the specified positions.
  <p>
  Example:
  <pre class="groovyTestCase">
  assert [1, 3, 2, 4] == [1, 2, 3, 4].swap(1, 2)
  </pre>
  
  @param self a List
  @param i a position
  @param j a position
  @return self
  @see Collections#swap(List, int, int)
  @since 2.4.0