public java.util.List<String> getGroups() {
        if (groups == null) {
            groups = new com.amazonaws.internal.SdkInternalList<String>();
        }
        return groups;
    }
<p>
The IDs of the security groups. You cannot specify security groups from a different VPC.
</p>

@return The IDs of the security groups. You cannot specify security groups from a different VPC.
aws-java-sdk-ec2/src/main/java/com/amazonaws/services/ec2/model/AttachClassicLinkVpcRequest.java