code: public DescribeRdsDbInstancesRequest withRdsDbInstanceArns(String... rdsDbInstanceArns) {
          if (this.rdsDbInstanceArns == null) {
              setRdsDbInstanceArns(new com.amazonaws.internal.SdkInternalList<String>(rdsDbInstanceArns.length));
          }
          for (String ele : rdsDbInstanceArns) {
              this.rdsDbInstanceArns.add(ele);
          }
          return this;
      }
docs: <p>
  An array containing the ARNs of the instances to be described.
  </p>
  <p>
  <b>NOTE:</b> This method appends the values to the existing list (if any). Use
  {@link #setRdsDbInstanceArns(java.util.Collection)} or {@link #withRdsDbInstanceArns(java.util.Collection)} if
  you want to override the existing values.
  </p>
  
  @param rdsDbInstanceArns
  An array containing the ARNs of the instances to be described.
  @return Returns a reference to this object so that method calls can be chained together.