code: public DescribeIndexFieldsRequest withFieldNames(String... fieldNames) {
          if (this.fieldNames == null) {
              setFieldNames(new com.amazonaws.internal.SdkInternalList<String>(fieldNames.length));
          }
          for (String ele : fieldNames) {
              this.fieldNames.add(ele);
          }
          return this;
      }
docs: <p>
  A list of the index fields you want to describe. If not specified, information is returned for all configured
  index fields.
  </p>
  <p>
  <b>NOTE:</b> This method appends the values to the existing list (if any). Use
  {@link #setFieldNames(java.util.Collection)} or {@link #withFieldNames(java.util.Collection)} if you want to
  override the existing values.
  </p>
  
  @param fieldNames
  A list of the index fields you want to describe. If not specified, information is returned for all
  configured index fields.
  @return Returns a reference to this object so that method calls can be chained together.