code: public TableKeysAndAttributes withAttributeNames(String ... attributeNames) {
          if (attributeNames == null)
              this.attributeNames = null;
          else
              this.attributeNames = Collections.unmodifiableSet(
                  new LinkedHashSet<String>(Arrays.asList(attributeNames)));
          return this;
      }
docs: Used to specify the attributes to be retrieved in each item returned
  from the batch get-item operation.
  
  @param attributeNames names of the attributes to be retrieved in each
  item returned from the batch get-item operation.
  @return the current instance for method chaining purposes