code: public java.util.List<String> getSubnetIds() {
          if (subnetIds == null) {
              subnetIds = new com.amazonaws.internal.SdkInternalList<String>();
          }
          return subnetIds;
      }
docs: <p>
  The IDs of one or more subnets. You can specify only one subnet per Availability Zone. You must specify at least
  one subnet, but we recommend that you specify two subnets for better availability. The transit gateway uses one
  IP address from each specified subnet.
  </p>
  
  @return The IDs of one or more subnets. You can specify only one subnet per Availability Zone. You must specify
  at least one subnet, but we recommend that you specify two subnets for better availability. The transit
  gateway uses one IP address from each specified subnet.