code: public static <T> Callable<T> callable(Runnable task, T result) {
          if (task == null)
              throw new NullPointerException();
          return new RunnableAdapter<T>(task, result);
      }
docs: Returns a {@link Callable} object that, when
  called, runs the given task and returns the given result.  This
  can be useful when applying methods requiring a
  {@code Callable} to an otherwise resultless action.
  @param task the task to run
  @param result the result to return
  @param <T> the type of the result
  @return a callable object
  @throws NullPointerException if task null