code: public void setRequestedEc2SubnetIds(java.util.Collection<String> requestedEc2SubnetIds) {
          if (requestedEc2SubnetIds == null) {
              this.requestedEc2SubnetIds = null;
              return;
          }
  
          this.requestedEc2SubnetIds = new com.amazonaws.internal.SdkInternalList<String>(requestedEc2SubnetIds);
      }
docs: <p>
  Applies to clusters configured with the instance fleets option. Specifies the unique identifier of one or more
  Amazon EC2 subnets in which to launch EC2 cluster instances. Subnets must exist within the same VPC. Amazon EMR
  chooses the EC2 subnet with the best fit from among the list of <code>RequestedEc2SubnetIds</code>, and then
  launches all cluster instances within that Subnet. If this value is not specified, and the account and region
  support EC2-Classic networks, the cluster launches instances in the EC2-Classic network and uses
  <code>RequestedEc2AvailabilityZones</code> instead of this setting. If EC2-Classic is not supported, and no
  Subnet is specified, Amazon EMR chooses the subnet for you. <code>RequestedEc2SubnetIDs</code> and
  <code>RequestedEc2AvailabilityZones</code> cannot be specified together.
  </p>
  
  @param requestedEc2SubnetIds
  Applies to clusters configured with the instance fleets option. Specifies the unique identifier of one or
  more Amazon EC2 subnets in which to launch EC2 cluster instances. Subnets must exist within the same VPC.
  Amazon EMR chooses the EC2 subnet with the best fit from among the list of
  <code>RequestedEc2SubnetIds</code>, and then launches all cluster instances within that Subnet. If this
  value is not specified, and the account and region support EC2-Classic networks, the cluster launches
  instances in the EC2-Classic network and uses <code>RequestedEc2AvailabilityZones</code> instead of this
  setting. If EC2-Classic is not supported, and no Subnet is specified, Amazon EMR chooses the subnet for
  you. <code>RequestedEc2SubnetIDs</code> and <code>RequestedEc2AvailabilityZones</code> cannot be specified
  together.