public java.util.List<String> getAddSubnetIds() {
        if (addSubnetIds == null) {
            addSubnetIds = new com.amazonaws.internal.SdkInternalList<String>();
        }
        return addSubnetIds;
    }
<p>
(Interface and Gateway Load Balancer endpoints) The IDs of the subnets in which to serve the endpoint. For a
Gateway Load Balancer endpoint, you can specify only one subnet.
</p>

@return (Interface and Gateway Load Balancer endpoints) The IDs of the subnets in which to serve the endpoint.
        For a Gateway Load Balancer endpoint, you can specify only one subnet.
aws-java-sdk-ec2/src/main/java/com/amazonaws/services/ec2/model/ModifyVpcEndpointRequest.java