final class Subscription {
    private final List<String> topics;
    private final ByteBuffer userData;
    private final List<TopicPartition> ownedPartitions;
    private Optional<String> groupInstanceId;
    private final int generationId  // new added

    public Subscription(List<String> topics, ByteBuffer userData, List<TopicPartition> ownedPartitions, int generationId) {
        this.topics = topics;
        this.userData = userData;
        this.ownedPartitions = ownedPartitions;
        this.groupInstanceId = Optional.empty();
        this.generationId = generationId;  // new added
    }

    public Subscription(List<String> topics, ByteBuffer userData, List<TopicPartition> ownedPartitions) {
        this(topics, userData, Collections.emptyList(), -1);
    }

    public Subscription(List<String> topics, ByteBuffer userData) {
        this(topics, userData, Collections.emptyList(), -1);
    }

    public Subscription(List<String> topics) {
        this(topics, null, Collections.emptyList(), -1);
    }

    // new added, the generationId getter 
    public int generationId() {
        return generationId;
    } 
}